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                    Ryan Hansanuwat                                                     Matthew West
           Architectural Undergraduate Student                               Regenerative Studies Graduate Student
                     Cal Poly Pomona                                                   Cal Poly Pomona
                   Pomona, CA 91768                                                  Pomona, CA 91768

                       Mark Lyles                                                   Pablo La Roche Ph.D.
              Architectural Graduate Student                                         Associate Professor
                    Cal Poly Pomona                                   Department of Architecture, Adjunct Professor Lyle
                   Pomona, CA 91768                                           Center for Regenerative Studies
                                                       Cal Poly Pomona
                                                                                     Pomona, CA 91768


The Tijuana Low Cost Sustainable House Prototype                 housing project for Tijuana. This paper discusses some of
explores the development and integration of sustainable          the prototypes that are under development in this project and
technologies for low-cost housing in Tijuana. This project       that are being tested in full-scale at the low-cost house under
emphasizes readily available materials and technologies that     construction at the Lyle Center for Regenerative Studies at
are appropriate for the cultural and economic conditions of      Cal Poly Pomona (Fig. 1). The prototypes discussed in this
Tijuana. Students and Faculty of the Department of               paper are a recycled plastic bottle thermal mass wall system,
Architecture and the Lyle Center for Regenerative Studies at     a low-cost window prototype, low-cost green roof, and
Cal Poly Pomona’s College of Environmental Design, are           papercrete walls.
working on a full-scale prototype of a house at the Lyle
Center for Regenerative Studies, in which several low-cost
sustainable systems are being tested.


Sustainable architectural principles are being incorporated
into more buildings every day, but they are still out of reach
of many low income families. Nevertheless, many
traditional societies learned to build collaborating with
nature, basing their buildings on an intuitive knowledge of
the environment and climate, constructing buildings at a
very low cost. In the development of this project we             Figure 1: Tijuana Low-Cost Prototype House under
implemented strategies and systems based on proven               construction at the Lyle Center at Cal Poly Pomona.
traditional principles of sustainability, combining them with
more advanced technologies but that could still be built at      2. TIJUANA
very low costs, with local materials, providing adequate
thermal comfort while being sustainable. A significant           2.1 The climate of Tijuana
reduction in performance would be acceptable if the cost
reduction is significant.                                        Tijuana is a temperate climate with moderate winters and
                                                                 summers. The temperatures during the winter range from 5
This research project explores the development and               C to 23 C, and in the summer they range from 18 C to 30 C.
integration of low-cost technologies in a very low cost          The biggest challenge for existing homes in Tijuana is that
interior temperatures tend to closely track exterior            making it possible to build in these steep and very
temperatures because most homes do not have heating or          dangerous slopes.
cooling systems, or insulation. This creates thermally
uncomfortable spaces, which can also be dangerous to the
dwellers, especially the smaller children, the sick, or the
elderly who cannot stay warm enough in the winter nights.

We did not find climate data for Tijuana but used the
climate data for San Diego, located just to the north. The
psychometric chart in Climate Consultant indicated that
passive strategies can provide thermal comfort year round
(Fig. 2). Thermal comfort can be achieved with passive
solar heating in the winter, and night flushing with thermal    Figure 3: Plan phase 2
mass or daytime ventilation during the summer.

                                                                Figure 4: Section phase 2

                                                                4. THERMAL MASS WALL WITH RECYCLED
                                                                PLASTIC BOTTLES
Figure 2: Analysis of data using Climate Consultant 3.
                                                                4.1 Purpose of wall prototype

3. THE PROTOTYPE                                                The need for insulation and thermal massing in low-cost
                                                                Tijuana housing is evident. Many houses currently built are
The goal of the house is to create low cost sustainable         made of inexpensive, recycled, local materials. Many of
housing for the residents of Tijuana. The house will have       them have been built using recycled garage doors or even
very low construction and operating costs, providing            left-over pallets. These systems have sufficed to provide
comfortable spaces year round, security for the residents and   shelter for the families, but have done little to maintain
should be easy to build using local materials and labor,        interior temperatures at a comfortable level. What this
while integrating indoor and outdoor spaces to offer greater    prototype attempts to do is to utilize similar inexpensive,
usability of the individual sites.                              recycled local materials, but provide added value by
                                                                providing for passive heating and cooling, providing for
Because of the complexity of sustainability issues the          mechanisms of heat transfer, thermal mass, and insulation.
students in this team proposed to focus on three main
objectives: local sustainable building materials, use of        Previously, in order to achieve thermal mass, builders would
passive heating and cooling systems, adaptation to local        have to make many sacrifices. Walls could be made with
topography and site restrictions.                               poured concrete, but this is an expensive solution for the
                                                                area and can be dangerous if constructed improperly. Most
The project evolves from an “L” form to a “U” shaped            of the 2x4 walls are built using only the studs and the
building that maximizes surface to the south, while             exterior plywood. There are no interior materials.
permitting cross ventilation through the spaces as needed.
Simple elements, textures and natural materials are used to     The bottle wall solves both of these needs, inexpensive,
give a feeling of “home” to the building. Three gabion walls    readily available materials, while providin thermal mass that
that can be adjusted help to regulate the topography, which     can be used with passive heating and cooling systems to
is an important consideration in Tijuana’s colinas. Even        provide thermal comfort. It is designed to be constructed
though these gabion walls might seem high (fig 4) they can      using only three materials, recycled PVC tubing, recycled 2-
be adjusted to different heights depending on the slope         liter soda bottles, and concrete or earth. The PVC tubing
holds the bottles, while they extend beyond the wall. The
bottles are filled with water and absorb the heat throughout     4.3 Performance of the Wall
the day. They can be fixed in place or be removable, so that
they can be placed on a south-facing wall to collect heat,       Summer
and can be brought to other parts of the house to radiate the    During the summer months, the biggest concern is with
heat during the night. In order to prevent infiltration          shading during the daytime to prevent heat gains into the
between the PVC tube grid, a filler is placed in the open        space, and ventilation during the night. The exterior cover
spaces.                                                          folds up to shade the wall from the high winter sun, while
                                                                 still allowing for ventilation as needed (Fig. 4a). During the
4.2 Construction of the Wall                                     night, there are some cases where night flushing with high
                                                                 thermal mass can be advantageous. For such a need, the
The wall is designed to be built using local labor. The basic    upper rows of bottles can be removed, allowing for air to
concept of the wall is a grid of recycled PVC tubes tied         flow through the building as needed (Fig. 4b), this will
together and then to a studded wall. The tubes are cut at a      lower the internal temperature to a more comfortable level.
thirty degree angle into pieces that will fit within the width   With walls placed on opposite ends of the space, cross-
of the stud wall. String or twine is tied onto the ends of the   ventilation is achieved. As the wind passes around and
tubes to keep the bottles from sliding out of the holders.       through the wall, it cools the bottles on the outside, and
They are then tied to each other using available material        cools the space on the inside.
such as string or twine. For infiltration purposes lengths of
weather strip can be inserted into the tubes if available.
Once the grid is complete, the wall is erected into place and
tied or nailed to the studs.

Concrete or mud is placed into the cracks left between the
circular tubes and left to cure. Once the wall is complete,
empty recycled plastic bottles are filled with water and
placed into each individual slot with caps facing into house
for ease of maintenance (Fig. 5).                                                       a                             b
                                                                  Figure 6: Summer conditions a: Daytime shading. b:
                                                                  Nighttime cooling.
                                                                 In the winter months, the spaces can be heated and insulated
                                                                 using the bottle wall. The water in the bottle will increase in
                                                                 temperature, mostly through the effects of exterior solar
                                                                 radiation (Fig. 7a). As the heat is stored into the water it is
                                                                 also transferred by waters’ convection effect into the wall.
                                                                 As the exterior temperature lowers, there is no solar
                                                                 radiation available to continue heating the bottles, and
                                                                 interior temperatures are lowered beyond the comfort level,
                                                                 the bottles are pulled into the wall, and an insulated back is
                                                                 closed on the exterior of wall (Fig. 7b). The heat stored in
                                                                 the water continues to radiate into the interior space. If heat
                                                                 is needed in other areas, the bottles can be removed and
                                                                 placed in other room, as a portable heating system, and
                                                                 leaving a cap on the empty holder. The bottles then heat up
                                                                 that space, while the stored energy from more water bottles
                                                                 in the wall continue to heat the original space.

Figure 5: Recycled Plastic Bottle Thermal Mass Wall
                                                                  For the foam shelf liner we have used Velcro to create a
                                                                  tight seal around the window when the shade is closed. If an
                                                                  open position was desired this material could be rolled or
                                                                  folded to a position above the window.

                                                                  We have also developed an exterior shutter system that
                                                                  would provide shade during the day when opened. At night
                                                                  the shutter would be closed to provide a layer of air between
                                                                  the exterior of the window and shade which would act as a
                                                                  second layer of thermal lag for the window. The frame
                                                                  would be hinged above the window allowing the shutter to
                          a                b                      be easily propped open during the day. For the purposes of
Figure 7: Winter conditions a: Daytime absorbing and              our tests we are using an old rain jacket but it is our intent
heating. b: Nighttime heating.                                    that any durable fabric could be substituted or recycled for
                                                                  this purpose. This material would be stapled to the frame
                                                                  which would be provided to the residents.

Starting with the least expensive 24” X 24” window                6. LOW-COST GREEN ROOF SOLUTION
available in the market we set out to develop a user-friendly
system that would make this window more efficient. We             A low cost green roof has been implemented on the larger
considered passive solar techniques that were consistent          west-facing roof of our prototype in order to provide to
with the total design of the house. In it current form this       provide protection from the hot afternoon sun. On top of the
window loses much heat due to infiltration and conduction         wood decking we have placed an impermeable layer of
in the winter and gained to much heat by radiation in the         plastic as a moisture barrier (Fig. 9). “Cal Earth” bags (rice
summer. The challenge was to allow as much solar radiation        sack material) are filled with a growth medium which is a
during the winter day as possible and retain this warmth          mixture of native soil and vermiculite (to reduce weight)
through the cold winter night. Our design consisted of a          and are placed on the roof in rows perpendicular to the slope
simple awning system coupled with an interior shade (Fig.         of the roof (Fig. 10). These bags are designed to store earth
8). Both of these features are operable thereby allowing for      and are very inexpensive, lightweight, easy to transport, and
solar radiation to penetrate when needed. The retention of        biodegradable to sunlight. They allow water to pass through
this collected energy is critical to maintaining comfort levels   them while containing the growth medium. The benefit of
within the structure so we wanted to make sure we used a          this bag system is that it allows the bags to be easily
material in our shading system that had a high R value but        transported onto the roof as well as providing a structure
that was also relatively inexpensive. With this in mind we        around the soil while allowing the roots to establish
selected an easy to find foam shelf liner that could be cut       themselves. When positioned on the roof the top side of the
into the correct dimension. The total cost of the window unit     bag was cut open and a variety of sedums and succulents
including exterior and interior shades would be about $45.        native to Tijuana were planted. These plants were chosen
                                                                  for their drought resistance, low maintenance, and shallow
                                                                  root systems.

                                                                  This green roof system is very inexpensive and its thickness
                                                                  can be adjusted from 3 to 10 inches. This allows for
                                                                  flexibility depending on the load that the roof can carry.
                                                                  Should one bag need to be replaced it is easy for it to be
                                                                  pulled out without having to replace the entire roof. A green
                                                                  roof provides several benefits over conventional roofs:
                                                                  reducing the storm water runoff, reducing CO2 levels,
                                                                  reducing solar loads in the winter and with the soil itself
                                                                  which is un-insulated and thermally coupled to the interior it
                                                                  can provide thermal mass for heat storage in the winter and
                                                                  as a heat sink in the summer.

Figure 8: Low-Cost Window Prototype System Parts
                                                                7.2 Construction and Performance of Papercrete

                                                                Due to its 60% waste paper content, papercrete is relatively
                                                                lightweight and boasts exceptional energy efficiency, R-
                                                                3/inch. Thus, a 10-12 inch thick wall can be expected to
                                                                have an R-30 performance. Preliminary results of
                                                                compression tests indicate that the material can perform as a
                                                                load bearing system up to one story. Blocks are stacked and
                                                                bonded together with a papercrete mortar, creating a solid
                                                                papercrete wall with minimal thermal bridging through the
                                                                wall as is experienced with stick frame wall studs. Doors
                                                                and windows can simply be cut out of a solid wall with a
                                                                chainsaw. Reinforcing rebar can be drilled vertically down
                                                                into the wall system after it has been erected. A wall system
Figure 9: Section of Cal-Earth green roof prototype.            would typically be finished with a protective coating of lime
                                                                plaster. The breathability of the lime allows moisture to
7. PAPERCRETE                                                   pass out of the wall should any accumulate within. A more
                                                                permanent seal could trap moisture inside and cause
7.1 Purpose of Papercrete                                       structural instability and provide a medium for mold
                                                                growth. The issue of moisture accumulation and its effects
Many homes within informal settlements of Tijuana               within Papercrete is still being investigated. At this time
experience poor thermal comfort during the winter months        research indicates that papercrete is most adaptable and best
due to lack of insulation and infiltration of cold air          suited for hot and dry climates where there is minimal
throughout the entire building envelope. Poor thermal           exposure to moisture.
comfort can be attributed to lack of sufficient funds and
materials to build a comfortable home. An analysis of
locally available waste materials was performed for the
design of a low cost, durable, energy efficient building
material that could be implemented throughout informal
settlements of Tijuana. Papercrete is comprised of waste
paper and cement. The material can be easily formed into
blocks and used for the construction of walls and roofs.
Tijuana generates a considerable amount of paper waste
though its numerous manufacturing facilities, office use, and
newspapers. Very little of this paper waste is recycled into
additional post consumer products. Papercrete takes
advantage of this abundant waste material.

                                                                7.3 Local Manufacturing of Papercrete

                                                                Papercrete can be easily manufactured on a local scale as
                                                                well as directly on the construction site. Waste paper does
                                                                not need to be pre shredded or manipulated in any way. For
                                                                example whole newspapers can be blended with water into a
                                                                paper pulp and then mixed with Portland cement. Cement
                                                                acts as a bonding agent within all the paper fibers. Sand can
                                                                also be added for additional compressional strength of the
                                                                material. Typically for a load bearing structure equal
                                                                portions by weight of paper, cement and sand would be
                                                                mixed together for the desired material. Papercrete can also
                                                                serve as an infill material for a non load bearing structure,
sand would not be required in this instance as it could         8. ACKNOWLEDGEMENTS:
inhibit the thermal resistance of the material reducing its     Financial support for this project was provided by the
energy efficiency qualities. A normal cement mixer is not       National Collegiate Innovators and Inventors Alliance.
suitable for the mixing of papercrete, as there is no way to
effectively rip the paper apart during the mixing process.      The following students also participated in the development
Many different mixers have been designed for the mixing of      of these systems in Pablo La Roche’s course ARC 333 in
papercrete, all with the commonality of blending the paper      the Spring of 2006: John K. Whitsett, Leslie Lum, Ruth Oh,
into a pulp during the mixing process. For the purposes of      Christy Perez, Julia Molina, Marina Moraes, and Diego
the prototypical structure being constructed at Cal Poly        Urrego.
Pomona a mixer was designed and constructed to be towed
behind a pickup truck. A giant drum set upon a rear axle        The following students have also collaborated in the
was designed to have a blade spin inside the drum as the        construction of the house:
mixer was towed behind the truck. This mixer had the            Students in ARC 499, Winter 2006 with Professors Kyle
capacity to mix 150 gallons of papercrete at a time.            Brown, Irma Ramirez & Pablo La Roche: Kristian Whitsett,
                                                                Kim Wehinger, Mauricio Carranza, Leslie Lum, Sonya
                                                                Students in ARC 333 Energy Conservation in the Spring of
                                                                06 with Professor Pablo La Roche:Dicle, Salvador, Ceja,
                                                                ,Mark Chak, Lesley Felton, Ryan Hansanuwat, Stacy
                                                                Hoppes, April KaufmanMichele,Ciavash Loghmani, Mark
                                                                Lyles,Sergio Marquez, Julia Molina, Marina Moraes, Ruth
                                                                Oh, Christy Perez, Alondra Rodriguez, Audrey Sato, Danny
                                                                Schapker, Diego Urrego,John K Whitsett.
                                                                Students in ARC 499, Spring 06 with Professor Irma
                                                                Ramirez: Wes Bassett, Ivan Contreras, Randy Machado,
                                                                Jimmy Macias, Ben Millet, Charles Thrash, Matty West
                                                                Masters of Science in Regenerative Studies: Matty West

                                                                Travel expenses to ASES 2007 were made possible by the
                                                                Lyle Center for Regenerative Studies at Cal Poly Pomona
                                                                and the President’s Travel Fund at Cal Poly Pomona.

Similar types of “blending” mixers can be designed for
stationary use and larger capacity. The potential for a
locally based, cooperative, papercrete-manufacturing
business is certainly apparent. A block making facility built
and run by local residents providing building material for
the community made of waste product could support a local
economy as well as the construction of energy efficient


It is expected that by utilizing low-cost, locally available
and recycled materials, thermal comfort can be achieved in
very low cost housing, benefiting residents that can not
afford to buy and operate heating and cooling systems.
Housing in Tijuana can utilize inexpensive sustainable
prototypes to maximize comfort while minimizing cost. The
results of this research should be disseminated to residents
in the area, so that the tenants can implement the changes
themselves without having to hire builders or specialists in
order to have a home that provides more thermal comfort
and is more sustainable.

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