HEATING UP - Hardwood Floors Magazine

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					                                                     HEATING UP
        Radiant heat and wood flooring are growing together
                                                                                   By Steve Baxter




A          word to flooring contractors feeling
           blindsided by the vigorous growth in
           demand for wood floors over radiant
heat: Relax.
  The basic rules haven’t changed for years,
                                                  Floors in Cedar Crest, N.M., near Albuquerque.
                                                  “We’re doing a lot of it here. New construction is
                                                  probably about 75 or 80 percent of our work.
                                                  High-end housing is where the wood flooring is
                                                  going, and the majority of those houses have in-
and with one exception they probably won’t        floor radiant heat, probably also about 75 to 80
anytime soon.                                     percent. So it’s a huge percentage of our work.
  Also, products and techniques being             Over the past three years demand has been very
developed to make radiant-floor heating systems   consistent,” Mullany says.
easier to install and more energy-efficient are      Industry associations concur.
also making those systems much more                  “It’s growing quite rapidly,” say Mickey
conducive to hardwood floors.                     Moore of the National Oak Flooring
  Now that you’re relaxed, get ready.             Manufacturing Association in Memphis, Tenn. “I
  “You’re going to see the trend throughout the   field a lot more calls here with regard to radiant
nation,” says Kevin Mullany of Benchmark Wood     heat systems. Over the last 12 months,




                                                    December 1999/January 2000   HARDWOOD FLOORS   29
                                                probably one out of 10 calls I get         MOISTURE CONTROL
                                                concerns radiant heat.”                    IS THE KEY
 Source List                                       “It’s a very popular way of heating,”   What hasn’t changed are the rules
                                                says Daniel Boone of the National          that call for meticulous, if not
 As always, the National Wood
                                                Wood Flooring Association in               obsessive, attention to the relative
 Flooring Association is a good source
                                                Ellisville, Mo. “Believe me, we get a      moisture contents of the floor and
 of information and for referrals to
                                                lot of calls on radiant heat here at the   adjacent materials — such as latex
 others who can help. Call NWFA at
                                                office.”                                   paint, mortar, stucco or anything else
 800/422-4556 (U.S.), 800/848-8824
                                                   There’s been a “dramatic increase
 (Canada) or 636/391-5161 (local and                                                       “wet.”
                                                in radiant floor heating,” says Larry
 international), or visit the NWFA Web                                                       Michael McSwain of McSwain’s The
                                                Drake of the Radiant Panel
 site at www.woodfloors.org. Here are                                                      Hardwood Floor Store installs floors
                                                Association, which represents
 some additional sources of                                                                in and around his home base of
                                                manufacturers, vendors and end-
 information on installing wood floors                                                     Cincinnati, where radiant heat is
                                                users of radiant-heating systems and
 over radiant heat:                                                                        growing but not yet commonplace.
                                                components. “Over the past 10 years
                                                                                           Heating contractors there appear to
                                                we’ve seen 30 percent plus per year
 National Oak Flooring                                                                     be experimenting with different kinds
                                                growth in the industry. It just keeps
 Manufacturers Association                                                                 of floor systems, so when he sees
                                                right on growing like crazy.”
 22 N. Front Street, Suite 660                                                             something new he checks with the
                                                   Why the increase in demand?
 Memphis, TN 38103                                                                         National Wood Flooring Association
                                                   “If you live in Minnesota and you
 Phone: 901/526-5016                                                                       and with members who live where
                                                have a hardwood floor, generally
 E-mail: info@nofma.org                                                                    radiant heat is more common.
                                                speaking in the wintertime the floor is
 Web site: www.nofma.org                                                                     The basic, long-standing rules call
                                                going to be cold,” Drake says. “But
                                                you put in radiant heat and all of a       for making sure job site moisture has
 The Hardwood Council                                                                      dissipated — the concrete slab fully
                                                sudden that floor becomes very
 P. O. Box 525                                                                             cured or the framed subfloor fully
                                                friendly — not only beautiful but also
 Oakmont, PA 15139                                                                         acclimated — and the heat has been
                                                very comfortable. So it’s basically
 Phone: 412/281-4980                                                                       turned on and run for some time.
 Web site: www.hardwoodcouncil.com              word of mouth,” he says, that is
                                                generating the demand.                     After that the flooring can be
 Brochure: “Installing Hardwood                                                            delivered to acclimate for two weeks
 Floors Over Radiant Heating”                      But there are reasons beyond
                                                comfort as well.                           or more.
                                                   “The system is more energy-               “The latest one we did — it was 1⁄2-
 Radiant Panel Association                                                                 inch quartersawn maple — actually
 (represents radiant panel                      efficient — that’s why people are
                                                using it,” says Ron Spiteri of Spiteri     acclimated at the job site for two
 manufacturers)                                                                            months,” says Spiteri.
 P. O. Box 717                                  Brothers in Napa, Calif., who installs
                                                “at least one, if not two,” wood floors      Some building contractors may
 Loveland, CO 80539                                                                        object to such delays, but Spiteri
 Phone: 970/613-0100                            over radiant heat a month. In the long
                                                run it’s going to save you money. And      says, “They don’t have a choice.
 Web site: www.rpa-info.com                                                                This person’s spending almost
                                                there’s a lot less dust blowing in the
                                                air,” compared with forced-air             $100,000 on her floors, I’m going to
 Stadler Corp.                                                                             guarantee it, and this is how I’m
 (radiant heat system manufacturer)             heating systems, he says.
                                                   Because the heat in a radiant           going to do it.”
 3 Alfred Circle                                                                             In order to “get the numbers
 Bedford. MA 01730                              system is transferred object-to-object
                                                (floor to feet, for example), lower        right,” as NWFA’s Boone puts it, a
 Contact: Andy Fiefhaus                                                                    moisture meter is an absolute
 Phone: 800/370-3122 or 781/275-3122            overall room temperatures can be
                                                maintained while achieving the same        necessity. The flooring manufacturer
 Fax: 781/275-5398                                                                         should be able to suggest what the
 E-mail: service@stadlercorp.com                comfort level. Also, there’s less heat
                                                loss by way of air infiltration from       numbers should be, based on the
 Web site: www.stadlercorp.com                                                             type of application and the local
                                                outside.
                                                   In     addition,     technological      climate. (See “Getting the Numbers
 Warmboard
                                                advances in the various components         Right,” page 48.)
 (radiant heat system manufacturer)
                                                of the radiant system — tubing,              All these precautions can
 9498 Barbur Boulevard, Suite 203
                                                monitors and controls, manifolds,          intimidate the inexperienced, but
 Portland, OR 97219
                                                and so on — have made it possible          according to Howard Brickman of
 Phone: 503/977-1011
                                                to reduce the maximum water                Brickman Consulting in Norwell,
 Web site: www.warmboard.com
                                                temperature circulating in the tubes       Mass., “It’s really pretty simple. I
                                                and maintain a more consistent level       mean, it’s really very simple: At a
 Wirsbo
 (radiant heat system manufacturer)             of heat.                                   given relative humidity, the floor’s
 5925 148th Street West                            The steadier, cooler temperatures       EMC [equilibrium moisture content]
 Apple Valley, MN 56124                         do more than save energy, of course.       is a certain percentage. If you
 Elaine Hoffman, Design Department              They answer the prayers of the floor       increase the humidity, it’s going to
 Phone: 800/321-4739 or 612/891-2000            man, because high, fluctuating             swell and if you decrease the
 Fax: 612/891-2008                              temperatures can exacerbate the            humidity, it’s going to shrink. It’s a
 Web site: www.wirsbo.com                       movement in the wood floor. And, of        direct relationship, and if guys will
                                                course, excessive movement is what         understand that, they can do
                                                can lead to floor failure.                 anything they want,” he says.

30    HARDWOOD FLOORS   December 1999/January 2000
        Fortunately, “the knowledge level          FINDING THE                                 “Right now,” says RPA’s Drake, “the
     in the industry has increased over            RIGHT SYSTEM                             knowledge we have about wood
     the years,” Brickman says. “In the            If the rules regarding radiant floors,   floors over radiant heat is mostly just
     past, about half my consulting                site conditions, and moisture            experiential knowledge — what’s
     business was going out and looking            contents are long-standing and widely    been done in the field.”
     at cupped floors and explaining to            accepted among those in the know,           According to Drake, a bright spot
     people that it was caused by                  there is no such agreement on the        on the horizon is an 18-month study
     excessive moisture on the underside.          subject of the different radiant-floor   being conducted by the American
     I get less and less of that. I think it’s     systems and their compatibility with     Society of Heating and Refrigeration
     mainly because people are a little            the different types of wood flooring     Engineers at Kansas State University.
     better educated.”                             available.                               “They have a research project that is
                                                                                            studying the convectivity or the
                                                                                            transfer of heat in all types of floor
                                                                                            sandwiches,” he says. “However, they
                                                                                            just built the test laboratory, so the
                                                                                            study is just at the beginning stages.”
                                                                                               For now, definitive answers to
                                                                                            questions about which flooring
                                                                                            materials are the best match for
                                                                                            which radiant floor systems will have
                                                                                            to wait. Floor installers will have to
                                                                                            play the hand they’re dealt and go
                                                                                            with what they know.
                                                                                               Around Albuquerque, 70 percent of
                                                                                            the radiant floors consist of plastic
                                                                                            tubes embedded in concrete-slab
                                                                                            subfloors, says Mullany. His company
                                                                                            occasionally directly glues down an
                                                                                            engineered product, and more often
                                                                                            installs a floating-floor system.
                                                                                               But mostly, he uses the traditional
                                                                                            solid, 3⁄4-inch tongue-and-groove wood
                                                                                            floor with two layers of 1⁄2 -inch
                                                                                            plywood subfloor over a vapor
                                                                                            barrier on top of the slab.
                                                                                               “We have the builder recess the
                                                                                            slab 11⁄4 inch,” he says. “Our total floor
                                                                                            thickness is going to be 13⁄4 inch, and
                                                                                            so by him recessing it 1 1⁄4 inch, we
                                                                                            match out flush with ceramic tile.”
                                                                                               On framed-wood subfloors, Mullany
                                                                                            can use the same technique, because
                                                                                            the builder typically positions the
                                                                                            tubes on top of the subfloor decking,
                                                                                            then floats the entire floor with 1 1⁄2
                                                                                            inch of gypsum cement.
                                                                                               “I don’t like the sleeper system at
                                                                                            all,” he says, referring to the more
                                                                                            common practice of running the
                                                                                            tubes between sleepers on top of the
                                                                                            subfloor. The problem is, the sleeper
                                                                                            placement “dictates where we’re
                                                                                            going to nail. The wood floor itself
                                                                                            should dictate where we’re going to
                                                                                            nail.”
                                                                                               Brickman doesn’t like the sleeper
                                                                                            system either. “Some of the radiant
                                                                                            heating manufacturers recommend
                                                                                            putting sleepers down 12 to 16 inches
                                                                                            apart, then pouring some kind of
                                                                                            cementitious material between them,
                                                                                            whether it’s gypsum cement or
                                                                                            lightweight concrete, then nailing
                                                                                            directly to the sleepers,” he says. “I
                                                                                            find that to be extremely risky for two
                                                                                            reasons. One, there isn’t enough

32       HARDWOOD FLOORS   December 1999/January 2000
 frequency of nailing there. That’s the        to dry properly,” Brickman says.          everywhere, so we really had to lay it
 major problem. Twelve inches is not              But in Napa, where wood-framed         out with the warm floors guy and the
 enough, especially when you have a            floors are typical, the sleeper system    contractor. It’s crucial.”
 subfloor that’s going to shrink a little      works for Ron Spiteri, who stresses          On the few occasions where Spiteri
 bit more than a standard floor                the importance of becoming involved       has been called on to lay a floor over
 because of the heat source.                   in determining the spacing and            a radiant slab, he’s used a solid-wood
    “The other thing is, a lot of times        location of the sleepers.                 floating floor system that goes
 there’s so much excessive moisture               “You need a nailing pattern. We’d      together with metal clips.
 in that lightweight concrete that it          rather nail than glue, and we like to        Brickman, too, favors the use of this
 saturates the subfloor, it saturates          nail every eight inches,“ he says. “The   product over a slab: “The metal clips
 the sleepers, and they don’t allow it         last house we did had borders             actually hold the pieces in relative
                                                                                         position, so when these pieces start
                                                                                         to shrink, the shrinkage occurs
                                                                                         between every board,” he says.
                                                                                            There is another approach to
                                                                                         combining wood subfloors and
                                                                                         radiant heat, RPA’s Drake says, noting
                                                                                         that an increase in installations where
                                                                                         the tubing is applied to the underside
                                                                                         of the subfloor, rather than
                                                                                         embedded in material of any kind.
                                                                                            One reason is the cost factor, he
                                                                                         says. “It’s much easier to just go in
                                                                                         and apply the tubing between the
                                                                                         joists without interrupting any of the
                                                                                         other construction. Also, by putting
                                                                                         the tubing in the joist space, we see
                                                                                         what we think to be a better
                                                                                         spreading of the heat underneath the
                                                                                         subfloor. And it allows the hardwood
                                                                                         floor to be nailed directly to the
                                                                                         subfloor.”
                                                                                            Insulation is typically applied
                                                                                         beneath the tubing, and aluminum
                                                                                         “fins” or plates are sometimes used to
                                                                                         help spread the heat.
                                                                                            When Mullany encounters such an
                                                                                         installation, he asks the builder to
                                                                                         “run some more tubing in there, to
                                                                                         reduce the chance of hot spots
                                                                                         causing movement inconsistencies in
                                                                                         the finished floor. That’s our only
                                                                                         request,” he says.

                                                                                         CHOOSING THE RIGHT
                                                                                         WOOD FLOORING
                                                                                         Because of its dimensional stabilty,
                                                                                         engineered wood flooring is often
                                                                                         recommended for use over radiant
                                                                                         heat. If solid wood flooring is to be
                                                                                         installed over radiant heat, quartersawn
                                                                                         lumber offers the best chance for a
                                                                                         successful installation.
                                                                                            Compared to plainsawn flooring,
                                                                                         “You’ll see up to a 50 percent reduction
                                                                                         in shrinking and swelling because of
                                                                                         the structure of quartersawn wood,”
                                                                                         says Brickman.
                                                                                            “We always use quartersawn
                                                                                         material, either 3⁄4 or 1⁄2 inch,” says
                                                                                         Spiteri. “It’s a must — I can’t express it
                                                                                         strongly enough.”
                                                                                            There is some dissension, however,
                                                                                         on the issue of 3⁄4-inch solid products
                                                                                         versus thinner ones — typically 1⁄2 -, 3⁄8-,


34   HARDWOOD FLOORS   December 1999/January 2000
     and 5⁄16- inch thick.                        may not affect 3⁄4-inch at all, but it is   they’re laid, plus the thickness of the
        “We’d rather use 1⁄2-inch material;       going to affect a 5⁄16-inch product. It’s   floor itself — substantially impacts
     it’s more stable,” says Spiteri.             not going to expand any more over           the efficiency of the radiant system.
        “There’s a line of thinking that          the long haul — perhaps it’ll expand           “All you’re really doing by having it
     those products are more stable,              less — but it’s going to react faster.”     thicker and having some insulation
     although I don’t know that I’ve ever           Mullany also doesn’t buy the              between the two is you’re slowing
     read anything that actually verified         argument that a buildup of material         down the reaction time from slab to
     that,” says Mullany. “It is proven           between the heat source and the top         room,” he says. “For radiant heat to
     that they do react more quickly, so          of the finish floor — such as those         be efficient, you want to just set your
     that if you have a five-day cycle of         two layers of 1⁄2-inch plywood, plus the    thermostat and leave it where it’s
     abnormally low or high humidity it           thickness of the slab over which            set,” he says, “so you only have one
                                                                                              little blip.”
                                                                                                 “We want that water cycling year-
                                                                                              round,” Mullany says. “We don’t
                                                                                              want that slab to completely cool,
                                                                                              because when the heat comes back
                                                                                              on you’re going to have additional
                                                                                              condensation.”
                                                                                                 Boone’s understanding of the

                                                                                                 “For radiant heat
                                                                                               to be efficient, you
                                                                                                 want to just set
                                                                                                your thermostat
                                                                                               and leave it where
                                                                                                     it’s set.”
                                                                                              efficiency question is different: “The
                                                                                              thicker you go with the subfloor or
                                                                                              the hardwood flooring product, the
                                                                                              more energy you use in the system.”
                                                                                                   At least one manufacturer of
                                                                                              quartersawn solid wood flooring
                                                                                              recommends gluing it down directly
                                                                                              on radiant-heated slabs, and some
                                                                                              might argue that gluing down 1⁄2-, 3⁄8- or
                                                                                              5
                                                                                               ⁄16- inch quartersawn flooring would
                                                                                              be the most energy-efficient —
                                                                                              reducing the total thickness of the
                                                                                              flooring system. However, says
                                                                                              Boone, “At this time the NWFA cannot
                                                                                              recommend that you glue a solid
                                                                                              product to concrete.”
                                                                                                   That could change, Boone suggests.
                                                                                              “There are some 12-inch products and
                                                                                                                   ⁄
                                                                                              some 38- and 516-inch products that are
                                                                                                        ⁄     ⁄
                                                                                              successfully installed over concrete.
                                                                                              It’s the 34-inch product installers have
                                                                                                          ⁄
                                                                                              had problems with,” Boone says. “So I
                                                                                              would say that within a year or so
                                                                                              there will probably be some changes
                                                                                              made” to the association’s installation
                                                                                              guidelines.
                                                                                                   Will the guys in the field embrace
                                                                                              these changes? Time will tell, but for
                                                                                              now, “We don’t like gluing wood
                                                                                              floors down because it’s harder on
                                                                                              your feet for standing, it’s harder to
                                                                                              replace, and the floor can’t move like
                                                                                              it’s supposed to,” Spiteri says.
                                                                                                   “It’s not something we want to

36      HARDWOOD FLOORS   December 1999/January 2000
                                                    pursue,” says Mullany. “We have
                                                    techniques that work day in and day
                                                    out, and when you have that and
                                                    when you’re building a reputation
                                                    based on it, you stick with it.”

                                                    CHANGES IN RADIANT
                                                    HEAT SYSTEMS
                                                    Some product designers are looking
                                                    for other ways to reduce the overall
                                                    thickness of the floor sandwich,
                                                    increase efficiency, and reduce
                                                    response time. EPA’s Drake says
                                                    there are several such products now
                                                    on the market that coincidentally
                                                    “make putting down a hardwood floor
                                                    a little easier” as well.
                                                        One is Warmboard — an
                                                    interlocking 1 3⁄3 2 -inch-thick wood
                                                    composite panel system that is used
                                                    as the actual subfloor. The 4-by-8-foot
                                                    panels are grooved on top to
                                                    accommodate the radiant tubing and
                                                    feature an unbroken aluminum skin.
                                                        Since walls are framed after the
                                                    subfloor is installed, the 12-inch-on-
                                                    center tubes can run without regard
                                                    for room layout. Hardwood floors can
                                                    be nailed directly into the
                                                    Warmboard. The 1⁄2-inch tubes are
                                                    clearly visible to the floor man.
                                                        Another panel product, called Quik
                                                    Trak, also features grooves for the
                                                    tubing and an aluminum component.
                                                    The 7-by-48-by-12-inch-thick panels are
                                                                       ⁄
                                                    designed to go over the top of existing
                                                    wood subfloors or concrete slabs, so
                                                    they can be used in retrofit applications
                                                    as well as in new construction.
                                                        The system is designed to accommodate
                                                     ⁄
                                                     16-inch tubing. Both the panels and the
                                                    5

                                                    tubing are manufactured by Wirsbo.

                                                    STAYING ON TOP
                                                    With the continuing evolution of
                                                    radiant-heat systems, wood flooring
                                                    contractors will face a challenge in
                                                    keeping up with recommendations for
                                                    installing over those systems. One
                                                    place to start, of course, is with the
                                                    manufacturers of the systems —
                                                    perhaps collecting a file of installation
                                                    procedures and guidelines for each.
                                                      With any system, most agree, a lot of
                                                    problems can be avoided if there’s
                                                    early communication and cooperation
                                                    among all involved — the flooring
                                                    contractor, builder, heating contractor,
                                                    plumber and owner. With that, the end
                                                    result is more likely to be in line with
                                                    everyone’s expectations. ●

                                                    Steve Baxter is a former building
                                                    contractor and occasional contributor
                                                    to Hardwood Floors.

38   HARDWOOD FLOORS   December 1999/January 2000
                                                    adhesive to use over radiant heat.
                                                      Gluing a solid strip product to a slab should be
                                                    attempted only if a flooring manufacturer does
                                                    recommend this method and then only if specific
                                                    instructions are followed.

                                                    • Single-layer, nail-down subfloor (See Figure 5.):
                                                    Usually over a slab or existing subfloor, 2-by-4 sleepers
                                                    are attached to the slab or subfloor, with tubes running
                                                    between the sleepers and a radiant slab poured over the
                                                    tubing.
                                                       The radiant slab needs to cure and dry, with the
                                                    heating system turned on, before a wood subfloor is laid
                                                    over it. The right moisture content may vary from one
                                                    region to another, but 8 to 12 percent moisture content
                                                    in the slab (which is usually compatible with 6 to 8
                                                    percent moisture content in wood flooring) is a good
                                                    average to aim for in many areas.
                                                       Once an acceptable moisture content has been
                                                    achieved, a 6-mil polyethylene or other approved vapor
                                                    barrier should be placed over the slab and sleepers, and
                                                    the wood subfloor should be laid. Many flooring
                                                    professionals recommend a minimum of 3⁄4-inch plywood
                                                    subfloor, screwed or nailed to the sleepers. Some prefer
                                                    using both glue and screws. Standard practice dictates
                                                    that a 1⁄4-inch to 1⁄2-inch expansion space be left around
                                                    each sheet of plywood and at the walls.
                                                       With the heating system still on, the wood subfloor
                                                    should dry to an acceptable moisture content (6 to 8
                                                    percent in many regions) before wood flooring is
                                                    brought into the structure. (In addition, the interior
                                                    environment should be stabilized at temperature and
                                                    humidity levels that reflect “normal living conditions.”)
                                                    Solid wood flooring should be broken out of bundles
                                                    and spread out in the area where it will be installed, and
                                                    allowed to acclimate to interior conditions. The National
                                                    Wood Flooring Association recommends that subfloor’s
                                                    moisture content be within 4 percentage points of the
                                                    wood flooring before installation is safe. Engineered
                                                    wood flooring may not need to acclimate prior to
                                                    installation.
                                                       Once the moisture content of all elements — radiant




                                                     NAIL IT
                                                     In any nail-down installation, wood flooring installers
                                                     must take care that nails don’t puncture the radiant-
                                                     heat tubing. It may be a question of accuracy: The
                                                     location of the tubing must be identified and avoided, or
                                                     nails should be driven into the sleepers or joists. Or it
                                                     may be a question of nail length: They should be short
                                                     enough not to penetrate the subfloor above the tubing. If
                                                     you’re nailing only into joists or sleepers, be aware that
                                                     joists are normally placed 16 inches on-center and
                                                     sleepers are often placed 12 inches on-center. The
                                                     National Oak Flooring Manufacturers Association’s
                                                     optimum nailing schedule for solid strip flooring is one
                                                     nail every 8 to 10 inches. The maximum allowable
                                                     distance between nails is 10 to 12 inches.




44   HARDWOOD FLOORS   December 1999/January 2000
                                                    slab, sleepers, subfloor and wood flooring — are in
                                                    balance, the flooring should be laid perpendicular to
                                                    the sleepers and blind-nailed through the subfloor to
                                                    the sleepers. After installation, standard practice
                                                    recommends that wood flooring be allowed to
                                                    acclimate from four days to three weeks (depending
                                                    on regional moisture conditions) before being sanded
                                                    and finished.

                                                    • Double-layer floating subfloor (See Figure 6.): This
                                                    system, preferred by some flooring professionals, is
                                                    commonly used over a cast-in-slab radiant-heat
                                                    system, with no sleepers required.
                                                      After the slab has cured and dried to an acceptable
                                                    level, place a 6-mil polyethylene (or other acceptable)
                                                    vapor barrier over the slab. Then float two layers of
                                                    wood — typically 1⁄2-inch plywood — over the slab. Lay
                                                    the first layer of plywood over the slab, with staggered
                                                    butt joints and expansion gaps of 1⁄8 to 1⁄4 inch around
                                                    each sheet and a 1/4-inch to 1⁄2-inch gap at the walls.
                                                    Some flooring professionals recommend spreading
                                                    adhesive over the first layer. Lay the second layer of
                                                    plywood over the first, with sheets perpendicular to or
                                                    at a 45-degree angle to the first layer and the seams
                                                    staggered so that no seam from the bottom layer is
                                                    uncovered. Leave a 1⁄8-inch to 1⁄4-inch expansion gap
                                                    around each sheet. Then screw the top layer to the
                                                    bottom with 3⁄4-inch wood screws, about 12 inches on-
                                                    center and 6 inches on the seams. Some flooring
                                                    professionals staple the two layers together, rather
                                                    than gluing.
                                                      Just as with the single-layer system, the subfloor
                                                    must be allowed to dry to an acceptable moisture
                                                    content before the finish flooring can be acclimated (if
                                                    necessary) and installed. Some flooring professionals
                                                    recommend placing 15-pound roofing felt between the
                                                    subfloor and the wood flooring.

                                                    • Engineered floating floor: This method works well
                                                    directly over a slab. Compared with solid wood, the
                                                    engineered wood flooring is less subject to expansion
                                                    and contraction as moisture content changes, but
                                                    what movement there is can be accommodated by the
                                                    entire floor moving over the slab. Like the glue-down
                                                    floors, engineered floating floors minimize height gain
                                                    and are also available in prefinished products to
                                                    eliminate sanding and finishing.
                                                       Place the recommended pad over the slab, then
                                                    float the floor over the pad. The floor is held in place
                                                    by gravity, not attached to the subfloor. Use the
                                                    manufacturer’s recommended adhesive for gluing the
                                                    flooring pieces together and follow manufacturers’
                                                    recommendations for expansion space at the walls.

                                                    • Solid floating floor: This system, which uses metal
                                                    clips to mechanically hold the flooring pieces
                                                    together, has many of the advantages of the
                                                    engineered floating system, including minimized
                                                    height gain. While solid wood is more susceptible to
                                                    expansion and contraction than engineered wood, the
                                                    floating system does allow the floor to move as a unit
                                                    to accommodate moisture-content changes. — R.B.



46   HARDWOOD FLOORS   December 1999/January 2000
                                                    INSTALLING OVER RADIANT HEAT:
                                                    GET THE MOISTURE
                                                    NUMBERS RIGHT
                                                         he key to a successful wood flooring installation over radiant heat is to
                                                    T    pay meticulous attention to the moisture content of the wood flooring,
                                                    subfloor, concrete slab and other surrounding materials, as well as the
                                                    interior environment of the structure. Your first priority is to follow the
                                                    flooring manufacturer’s recommended guidelines. However, the National
                                                    Wood Flooring Association has some general guidelines.
                                                       Before solid wood flooring can be installed in any application, it needs to
                                                    be properly acclimated to “normal living conditions.” That means that the
                                                    structure itself must be at “normal living conditions” before the wood floor
                                                    can be acclimated.
                                                       To be at “normal living conditions,” the structure must be totally
                                                    enclosed, with all “wet trades” work completed. The HVAC (heating,
                                                    ventilation and air-conditioning) system should be operating at occupancy
                                                    level. Finally, testing with moisture meters should show that materials in
                                                    the structure (especially the slab and subfloor) are acceptably dry, and
                                                    hygrometer tests should indicate that the relative humidity in the interior
                                                    environment is stabilized.
                                                       The wood flooring should then be allowed to reach the equilibrium
                                                    moisture content (EMC) that is consistent with the interior environment. In
                                                    most cases, this will be a moisture content of 6 to 9 percent. However,
                                                    proper moisture content will vary from one region to another and from one
                                                    season to another within regions.
                                                       In general, rely on the recommendations of your wood flooring
                                                    manufacturer or supplier for the length of time the slab and subfloor should
                                                    dry and for the proper moisture content.
                                                       Wood flooring at the right moisture content is only one step. In addition,
                                                    a wood subfloor should be within 4 percentage points of the wood flooring’s
                                                    EMC. That is, if the EMC of the wood flooring is 8 percent, the wood
                                                    subfloor should have a moisture content of no more than 12 percent.
                                                       For installation over a concrete slab, NWFA recommends that moisture
                                                    vapor emission from the slab should not exceed 3 pounds per 1,000 square
                                                    feet in 24 hours. Rely on your flooring manufacturer’s recommendations
                                                    for what moisture test to use.
                                                       Regardless of the season, make sure the heating system is turned on to
                                                    drive any excess residual moisture out of the slab or subfloor before the
                                                    wood flooring is acclimated and installed.
                                                       (However, once the slab and subfloor have been dried, the system must
                                                    be turned down or off before a glue-down installation can begin, since a
                                                    too-warm slab or subfloor will keep the adhesive from bonding properly.
                                                    For site-finished floors, the system should also be turned down or off
                                                    before finish is applied, since the heat can keep the finish from curing
                                                    properly.)
                                                       How long the radiant-heat system should be on is more problematic,
                                                    depending in part on what type of radiant-heat system is in place.
                                                    • In frame construction, the radiant-heat tubing may be installed by
                                                    stapling it to the bottom side of the wood subfloor. In those cases, it is
                                                    recommended that the radiant-heat system be operating at least 72 hours
                                                    prior to acclimating the wood flooring.
                                                    • When concrete is used as part of the radiant-heat system, you have the
                                                    additional problem of making sure the slab is cured and dry. That can take
                                                    anywhere from 30 to 60 days, and sometimes more. — R.B.

                                                    For a more detailed discussion of the relationship between moisture and
                                                    wood flooring, consult the National Wood Flooring Association’s Technical
                                                    Publication, Water and Wood. To obtain a copy, contact NWFA by phone at
                                                    800/422-4556 (U.S.), 800/848-8824 (Canada) or 636/391-5161 (local and
                                                    international), by fax at 636/391-6137; or by e-mail at natlwood@aol.com.
                                                    You can also visit NWFA’s Web site at www.woodfloors.org.


48   HARDWOOD FLOORS   December 1999/January 2000

				
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