NCDOI OSFM Evaluation Services
Scope of NCDOI Evaluations: The purpose of this document is to provide guidelines to
inspectors for clarification of code requirements or guidelines to inspectors for consideration
when presented with a method or material not prescriptively addressed by the building codes.
This evaluation contains the performance characteristics given by the code to determine if the
method or material meets the intent in accordance with Section 105 of the 2009 North Carolina
Administrative Code and Policies.
DOI File No: 003-10
Evaluation Date: March 30, 2010
Product Group: Cross Laminated Timber Construction
Code Editions: North Carolina State Building Code, 2009 edition; North Carolina State Energy
Conservation Code, 2009 edition, North Carolina State Administrative Code and Policies, 2009
1.0 Contents…………………………………………………………………Page 1
2.0 Intent……………………………………………………………………..Page 1
3.0 Scope…………………………………………………………………….Page 1
4.0 Code References……………………………………………………….Page 2
5.0 Issues and Recommendations………………………………………..Page 4
6.0 Submittals to the Authority Having Jurisdiction (AHJ)…………...…Page 7
7.0 Reference Standards…………………………………………………..Page 9
8.0 Technical References………………………………………………….Page 9
This report is intended to assist inspectors on subjects that may not be clear or cannot be
compared side-by-side. The report does not provide an evaluation of any vendor’s specific
product, nor does this report imply that the local inspector must approve a specific material
or method based on this material. The user of this document should exercise his judgment
in the application of recommendations contained herein.
Cross Laminated Timber (CLT) construction consists, essentially, of plywood panels
manufactured from board lumber laminated in layers. Boards in each layer are placed
perpendicular to the adjacent layers, hence the term “cross laminated.” Currently
manufactured only in Europe, board thicknesses range from 19 mm (about ¾”) to 40 mm
(approximately 1 ½”). With 3 to 8 laminations, panel thickness can range from 57 mm
(roughly 2 ¼”) to 320 mm, (slightly less than 13”). Panels may be manufactured in sizes
up to 16,500 mm (approximately fifty-four feet) by 2950 mm (approximately 9’-8”).
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Lumber species are typically European softwoods, primarily European species of
To date CLT construction has been confined to Europe. For the past couple of years
Woodworks, a United States based wood industry trade organization, and the American
Plywood Association have promoted the use of CLT construction in the United States.
To date, no manufacturer has opened a plant in the United States; although, at least one
European manufacturer has expressed interest in opening a U.S. facility.
Building codes in the United States, including the International Building Code published
by the International Code Council and the National Design Specification for Wood
Construction published by the American Wood Council, do not yet explicitly address CLT
construction. There are, however, some provisions implicit to all types of building
construction that also apply to CLT construction. Since the North Carolina State Building
Code (NCSBC) is modeled on the IBC, it also lacks specific provisions for CLT
construction. European building codes, laws, and ordinances, under which CLT
construction has been regulated to date, differ from United States codes, laws, and
ordinances significantly in philosophy and approach to fire resistance. For this reason,
European codes may not be appropriate as alternate means of compliance to the North
Carolina State Building Code.
This document is intended to define the conditions under which CLT may be accepted
as an alternate means of construction in North Carolina.
4.0 Code References
North Carolina State Building Code (NCSBC)
o Chapter 3 Use and Occupancy Classification – classifies buildings by
o Table 503 Allowable Height and Building Areas – limits height and floor area
of a building based on construction type and occupancy. Table 503 is intended
to limit the fire loading of the building to a level manageable by the local fire
o Section 504.2 Automatic Sprinkler System Increase – allows the building
height limitation from Table 503 to be increased by 20 feet and the maximum
number of stories to be increased by 1 when the building is fully sprinklered with
an NFPA 13 system or an NFPA 13R system. However, if an NFPA 13R system
is used, the building height cannot exceed 60 feet, and the number of stories
cannot exceed four.
o Section 509 Special Provisions – allows an additional story for a parking
garage in certain occupancies when in compliance with the stated separation
o Section 602 Construction Classification – defines building construction types.
o Table 601 Fire-Resistance Rating Requirements for Building Elements –
specifies structural fire resistance ratings for various types of construction.
Structural fire resistance ratings are intended to prevent collapse of the structure
long enough for fire fighters to respond to the event and have a reasonable
chance of extinguishing the fire.
o Table 602 Fire-Resistance Rating Requirements for Exterior Walls Based on
Fire Separation Distance – specifies fire resistance ratings for exterior walls
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based on distance from the assumed or actual property line, occupancy, and
construction type. These requirements are intended to limit the spread of fire
from one building to another.
o Chapter 7 Fire-Resistance-Rated Construction – specifies detailed
requirements for fire resistance rated assemblies intended for use in
compartmentalizing the building in order to limit fire load, protect structural
elements, separate specific hazards, or protect exit access and exits.
o Chapter 8 Interior Finishes – imposes fire safety requirements on interior
o Section 903 Automatic Sprinkler Systems – requires sprinkler systems for
hazardous, residential and institutional occupancies. Establishes maximum fire
area sizes for other occupancies above which automatic sprinkler systems are
required. Fire area sizes are intended to limit the fire loading in a fire area to a
level manageable by the local fire department.
o Chapter 14 Exterior Walls – addresses moisture penetration and structural
issues regarding wall claddings. Section 1406 places limitations on combustible
claddings, balconies, and bay windows.
o Chapter 15 Roof Assemblies and Rooftop Structures – Addresses moisture
penetration, fire resistance, and wind resistance issues associated with roof
o Chapter 16 Structural Design – establishes structural loading criteria for
o Chapter 17 Structural Tests and Special Inspections – Sections 1703,
1710.2, and 1714 establish the structural testing and inspection requirements for
and conditions for approval of materials not specifically addressed by the code or
in the standards referenced by the code. Special inspections specified in Section
1704 address detailed inspections conducted by third party inspection agencies,
acting under the direction of the authority having jurisdiction, required during the
construction phase in order to verify structural integrity is maintained. Special
inspections are conducted at the expense of the owner or his agent.
o Section 2304.11 Protection Against Decay and Termites – specifies minimum
requirements for protection against insect attack and decay. Sills and sleepers
between foundation slabs and CLT wall panels must be preservative-treated.
CLT panels exposed to weather or earth must also be preservative-treated.
Most of North Carolina is hospitable to termites; therefore, termite control is
required complying with Section 2304.11.6.
o Section 2603 Foam Plastic Insulation – establishes conditions for usage of
foam plastic insulations in roofs, walls, attics, and crawl spaces.
North Carolina State Energy Conservation Code (NCSECC)
o Chapters 4 and 5 - establish minimum requirements for energy efficiency,
including heat loss limitations, measures to limit air infiltration, and moisture
North Carolina Administrative Code and Policies (NCACP)
o Section 105.2 – establishes the authority of the AHJ to require any tests or
analysis necessary to substantiate claims an alternate material or method
complies with the intent of the technical codes.
o Section 106.2 – establishes minimum requirements for contract drawings
submitted to the inspection department and allows the AHJ to request any
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additional data necessary to describe the construction or installation of a product
North Carolina General Statute §160A-436 – enables municipalities to establish
primary and secondary fire districts, and prohibits the construction of wood frame
structures in the primary fire district. In addition, the law allows the municipality to
regulate wood frame construction in the secondary fire district.
5.0 Issues and Recommendations
A. Product Testing – To date, most testing on CLT panels has been conducted under
proprietary programs by the panel manufacturers or by European testing agencies not
currently approved in North Carolina. Testing must be conducted by approved and
certified independent testing agencies.
B. Design by Registered Design Professionals – Buildings constructed from CLT must
be designed by Registered Design Professionals competent in the disciplines of
architecture and structural engineering.
C. Type of Construction -
1. Type V Construction - Wood is a combustible material. According to Section
602 of the NCSBC, the only type of construction allowing combustible materials
in exterior bearing walls unconditionally is Type V Construction, wood frame.
Generally speaking, CLT buildings with combustible exterior walls will be
classified as Type V Construction. North Carolina General Statute §160A-436
prohibits Type V Construction in the primary fire district and allows the local
jurisdiction to regulate Type V Construction in the secondary fire district.
Therefore, CLT structures classified as Type V Construction cannot be located in
the primary fire district and may be restricted in the secondary fire district.
2. Type IV Construction
(a) There is a specific set of circumstances whereby CLT construction can be
classified as Type IV. Fire retardant treated wood framing is allowed in the
exterior walls of Type IV Construction when the walls require a fire resistance
rating of two hours or less. Furthermore, all bearing wall panels must have a
thickness no less than 8” nominal, the minimum thickness required for a
wood column in Type IV Construction. Fire retardant treating the exterior wall
panels, maintaining a minimum wall panel thickness of 8” nominal, and
maintaining floor and roof panel thicknesses in accordance with Section
602.4 would qualify the building for a Type IV classification.
(b) Type IV Construction would be permitted in both the primary and secondary
(c) Fire retardant treated panels must comply with Section 2303.2 of the NCSBC.
This section defines fire retardant treatment in terms of an extended ASTM E
84 test. In order to be considered fire retardant treated, a material must test
at a flame spread of 25 or less and show no evidence of progressive
combustion during a twenty minute extension of the test. In addition, the
flame front cannot progress more than 10.5 feet from the centerline of the
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D. Height Limitations – Although CLT buildings have been constructed in Europe up to
nine stories in height, in North Carolina the building height will be limited by Table 503 of
the NCSBC. Height modifications are permissible for sprinklering the building under
Section 504.2. Addition of a story for a parking garage, open or enclosed, at grade or
one story below grade, is permitted under the conditions stated in Sections 509.2 and
509.4. Even with these height modifications Type IV Residential structures with a
parking level could not exceed six stories in height, and Type VA Residential structures
with a parking level could not exceed five stories in height. Fire performance information
provided by manufacturers to date has not justified allowing taller buildings.
E. Fire Resistance Ratings –
1. Fire resistance ratings published by the manufacturers are structural ratings
based on European calculation techniques. These ratings do not consider
temperature rise on the side of the panel opposite the fire or flame passage
through panel joints. Structural fire ratings satisfy only the requirements of Table
601. Exterior wall ratings required by Table 602, firewalls, fire barrier walls, fire
partitions, smoke barrier walls, and floor/ceiling assemblies used as horizontal
fire barriers or tenant separation all must limit temperature rise on the opposite
side of the assembly from the fire and must limit flame passage in addition to
structural rating requirements.
2. For wood products produced in the United States, Technical Report 10
“Calculating the Fire Resistance of Exposed Wood Members” published by the
American Wood Council addresses calculated structural fire resistances for wood
decking, heavy timber beams, laminated beams, heavy timber columns, and
laminated columns. While this procedure is similar to European calculation
procedures, no domestic testing has been conducted to date to verify the
applicability of this document to laminated wood panel products. Consequently,
panels must be tested in accordance with ASTM E 119-00 in order to determine
the fire rating for all or any of the three requirements, structural, temperature rise,
or flame passage. Fire ratings requiring temperature rise limitations and/or flame
passage limitations should include treatment of panel joints tested in accordance
with ASTM E 1966.
3. Protection of metal connection devices must also be addressed, possibly with
intumescent coatings or spray fireproofing.
4. Application of gypsum board to the panel may be necessary to affect the
desired fire rating. If so, the entire assembly should be tested in accordance with
ASTM E 119-00.
5. Wall opening protection should be provided in accordance with the applicable
section of Chapter 7 of the NCSBC for all rated assemblies, unless the required
fire resistance rating is a consequence of Table 601 only.
F. Structural Integrity –
1. Structural Testing - The NCSBC references the National Design Specification
for Wood Construction published by the American Wood Council for structural
design of wood structures. Currently, the National Design Specification does not
address CLT products. As a result, design strength of the panels must be
established by testing in accordance with ASTM E 72. Axial load capacity,
transverse loading capacity, and racking capacity must all be addressed in the
testing. Tests must be conducted for each combination of lumber species,
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lumber grade, adhesive, and number of laminations the manufacturer intends to
produce. Racking tests should include a study of the effects of wall openings on
panel shear capacity and panel shear stiffness.
2. Connections - Connections utilizing nails, bolts, and lag screws may be
designed on the basis of the National Design Specification, provided the dowel
bearing strength is established through testing in accordance with ASTM D 5764-
97a. Design capacities of proprietary connectors should be established by the
connector manufacturer specifically for CLT.
3. Seismic Design - For seismic design, Table 12.2-1 of ASCE 7-05 has no
provision for CLT shear walls; consequently, the response modification factor
(R), the system overstrength factor (Ωo), and the deflection amplification factor
(Cd) must be established by dynamic testing. For seismic applications the panels
must be tested in accordance with ASTM E 2126-09.
G. Manufacturer’s Quality Control – The manufacturer should develop a quality control
program complying with ICC-ES AC 10 and ICC-ES AC 196. An approved and certified
independent testing agency should monitor the quality control program.
H. Exterior Cladding Issues – Issues the designer must address associated with the
building cladding include the following:
1. Moisture Penetration – Section 1403.2 requires the building to be weather
resistant. Moisture must be managed with a drainage cladding system, a barrier
type system, or a rain screen system. Appropriate flashings and sealants must
be provided at all exterior wall openings and interfaces between differing
cladding materials. Barrier type cladding systems must be tested in accordance
with ASTM E 331, and the test must include at least one wall opening, at least
one control joint, at least one wall/eave interface, and at least one wall sill. CLT
panel surfaces exposed to the weather must be stained, painted, or otherwise
coated to protect the surface. CLT panel surfaces at drainage planes must be
protected with liquid applied or membrane moisture barriers.
2. Energy Efficiency – CLT panels have some insulating capacity, but not enough
to solely comply with the requirements of the North Carolina State Energy
Conservation Code. Supplemental insulation is, therefore, normally required. If
the insulating value of the CLT panel is to be considered in designing the thermal
envelope, then the panel R value must be determined by testing in accordance
with ASTM C 1363. Foam plastic insulations must comply with Section 2603.5 of
the NCSBC. When the foam plastic insulation is applied to the exterior of the
CLT panels, the panels may act as a thermal barrier provided the panel joints are
detailed to prevent the temperature on the interior face of the panels from
exceeding 250oF after 15 minutes of fire exposure complying with the ASTM
E119 standard time-temperature curve.
3. Moisture Vapor Transmission – According to Sections 402.5 and 502.5 of the
North Carolina State Energy Conservation Code the designer must provide a
design capable of managing condensation associated with moisture vapor
transmission through the building envelope. CLT panels are considered vapor
permeable. As a result, a vapor retarder must be provided in Climate Zone 5,
unless the designer can show by calculation that deleting the vapor retarder will
not facilitate a moisture problem within the wall assembly.
4. Air Infiltration – Air infiltration must be limited as a requirement of Sections
402.4 and 502.4 of the North Carolina State Energy Conservation Code. CLT
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panels may be designed to act as an air retarder provided the panel joints and
panel interfaces with doors and windows are properly sealed. Otherwise, a liquid
applied or membrane air barrier may be necessary.
5. Combustible Veneers – If classified as a Type IV Construction, wood veneers
are limited to three stories from grade or 40 feet in height. If the veneer is fire
retardant treated, then the wood veneer on a Type IV building may extend four
stories from grade. Veneers above these levels on a Type IV building must be
noncombustible. Vinyl siding is not allowed on a Type IV building. Wood
veneers or vinyl siding on a Type V building may extend the full height of the
6. Structural Support of the Cladding – Cladding may be supported off of the
foundation, or, with the exception of masonry veneer, cladding may be supported
on the CLT exterior wall panels. The cladding support system and connections
to the CLT panels must be designed in accordance with Chapter 16 of the
NCSBC. Codes prohibit supporting masonry veneers on combustible
construction; consequently, masonry veneers must be supported off of the
foundation, or a secondary noncombustible framing system must be provided.
Masonry veneers supported off of the foundation are limited to 30 feet in height.
7. Environmental Movements – Thermal movements, shrinking and swelling of
materials due to changes in moisture content, and creep must be considered in
the design of the cladding system. Gravity load deflections in the supporting
structure and lateral movements due to wind and seismic loadings must also be
I. Panels Exposed As an Interior Finish – CLT panels with interior surfaces exposed as
finishes must be tested in accordance with ASTM E 84 and comply with the flame
spread limitations in Section 803 of the NCSBC.
J. Special Inspection – Special Inspection is required under Section 1704.13 of the
NCSBC for any material or system deemed to be an alternative to the materials and
systems prescribed in the NCSBC. Special Inspection for CLT systems should include:
1. Review of the fabricator’s quality control manual and third party certification.
2. Verification that the CLT panels delivered are consistent with the design
parameters specified in the Contract Documents.
3. Continuous inspection of the foundation system, including installation of all
devices required to anchor the CLT panels to the foundation.
i. Special inspection of soils must comply with Table 1704.7.
ii. For pile or pier foundations comply with Table 1704.8 or Table 1704.9.
iii. Concrete special inspection shall comply with Table 1704.4.
4. Provide periodic inspection of installed CLT panels to verify correct installation of
all panel connections and joint treatments.
5. On multi-story buildings verify floor to floor alignment and plumb of bearing wall
panels. Tolerances should be supplied by the manufacturer and justified by
stability calculations prepared by a Registered Design Professional.
6.0 Submittals to the Authority Having Jurisdiction (AHJ): Required and/or Upon Request
A. Contract Documents – Project specific Contract Documents should be submitted to the
AHJ in accordance with Section 106.2 of the North Carolina Administrative Code and
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Policies. Contract Documents should include drawings of all trades relevant to the
project, specifications, statement of special inspections, and schedule of special
inspections. Drawings and specifications must be sufficient to adequately define the
scope of work, including the geometry and material properties of CLT products. Signed,
dated seals of the design professionals in responsible charge of preparing the
documents must appear on the drawings and specifications. Structural drawings and
specifications should clearly identify the out of plane bending strength, the axial strength,
the in-plane shear strength, the modulus of elasticity, the shear modulus, and the panel
section properties assumed in the design. In addition, Architectural drawings should
contain a complete code summary sheet based upon Appendix B of the North Carolina
Administrative Code and Policies. Standard design details for tested fire rated
assemblies should be included with the code summary.
B. Manufacturer’s Shop Drawings – The CLT panel manufacturer should provide
fabrication and erection shop drawings specifying panel arrangement, panel profiles,
onsite storage requirements for panels, panel lifting points, installation instructions,
project specific connection details, temporary bracing required during construction, and
erection tolerances. Shop drawings should be checked by the structural engineer of
record and the architect of record and should bear their signed, dated shop drawing
stamps. If the panels are designed by the manufacturer or contractor based on a
performance specification prepared by the designers of record, then the shop drawings
should also bear the seal of the professional engineer hired by the manufacturer or
contractor to design the panels.
C. Panel Structural Design Calculations – When CLT panels and/or panel connections
are designed by the manufacturer or contractor on the basis of a performance
specification prepared by the designers of record, structural design calculations should
be submitted. Calculations should be sealed by the professional engineer hired by the
manufacturer or the contractor. In addition, the signed, dated shop drawing stamp of the
structural engineer of record should appear on the calculations, indicating he has
checked the design, agrees with the design, and has coordinated the panel design with
the foundation design.
D. Manufacturer’s Literature - Check manufacturer’s literature against Contract
Documents. Manufacturer’s literature provided should include:
1. Manufacturer’s standard structural design tables.
2. CLT panel material properties for indicated combinations of lumber species,
lumber grades, and adhesives.
3. CLT panel design geometric properties (area, moment of inertia, and section
modulus) for various number of laminations and thicknesses of laminations.
4. Standard connection details.
5. CLT panel fire ratings.
E. Test Data – Results of applicable tests conducted in accordance with the standards
indicated in the Reference Standards section of this paper should be submitted to the
F. Labeling of Individual Panels - Each panel should be labeled, embossed, stamped, or
branded with an identifying label. Appearing on each label should be the logo and
contact information of the independent third party inspection agency responsible for
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monitoring the plant quality control. Lumber grade, adhesive, out of plane bending
strength of the panel, axial strength of the panel, in-plane shear strength of the panel,
modulus of elasticity, and shear modulus should also appear on the label, or a grade
mark should appear on the label keyed to the manufacturer’s standard load tables
associated with the respective design material properties of the panel. If the panel
requires a fire resistance rating, the label should so indicate. A separate label should
appear on fire retardant treated panels containing the information required by Section
2303.2.1 of the NCSBC.
G. Special Inspection Reports – As required by Section 1704.1.3, the special inspector
must submit reports to the AHJ and to the design professional of record.
7.0 Reference Standards
ASTM C 1363-05, Standard Test Method for Thermal Performance of Building Materials
and Envelope Assemblies by Means of a Hot Box Apparatus.
ASTM D 5764-97a (2002), Test Method for Evaluating Dowel Bearing Strength of Wood
and Wood-Based Products.
ASTM E 72-02, Standard Tests Methods of Conducting Strength Tests of Panels for
ASTM E 84-04, Test Methods for Surface Burning Characteristics for Building Materials.
ASTM E 119-00, Test Methods for Fire Tests of Building Construction and Materials.
ASTM E 331-00, Test Method for Water Penetration of Exterior Windows, Skylights,
Doors, and Curtain Walls by Uniform Static Air Pressure Difference.
ASTM E 1966-00, Test Method for Fire Resistant Joint Systems.
ASTM E 2126-09, Standard Test Methods for Cyclic (Reversed) Load Test for Shear
Resistance of Vertical Elements of the Lateral Force Resisting Systems for Buildings.
ANSI/AF&PA NDS-2005, National Design Specification for Wood Construction, 2005
Edition, American Wood Council.
8.0 Technical References
Ward, Roxanne, “Going to New Heights Building the World’s Tallest Mixed-Use Wood
Structure,” Structure Magazine, August 2009.
WIS 2/3-61 “Cross Laminated Timber: Introduction for Specifiers,” TRADA Technology
Ltd., Buckinghamshire, U.K., April 2009.
WIS 2/3-62 “Cross Laminated Timber: Structural Principles,” TRADA Technology Ltd.,
Buckinghamshire, U.K., April 2009.
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John Vessby, Bertil Enquist, Hans Perersson, and Tomas Alsmarker, “Experimental
Study of Cross Laminated Timber Wall Panels,” European Journal of Wood and Wood
Products, Volume 67, Number 2, May, 2009, pp. 211-218.
Andrea Frangi, Mario Fontana, Erich Hugi, and Robert Jübstl, “Experimental Analysis of
Cross-Laminated Timber Panels in Fire,” Fire Safety Journal, Volume 44, Issue 8,
November 2009, pp. 1078-1087.
This document does not constitute an evaluation of any
vendor’s specific product, nor does this document
imply that the local AHJ is obligated to approve any
specific method or material.
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