Final Report: TrashWalls: Ultra Low-Cost Energy Retrofits (ULCER)

EPA Grant Number: SU835993
Title: TrashWalls: Ultra Low-Cost Energy Retrofits (ULCER)
Investigators: Richards, Robert F
Institution: Washington State University
EPA Project Officer: Page, Angela
Phase: I
Project Period: September 1, 2015 through August 31, 2016
Project Amount: $14,798
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet (2015) RFA Text |  Recipients Lists
Research Category: P3 Awards , Pollution Prevention/Sustainable Development , Sustainable and Healthy Communities , P3 Challenge Area - Sustainable and Healthy Communities


This project focuses on developing and testing a new approach to retrofitting energy conservation measures in rented residential buildings. Due to perverse incentives where landlords pay for capital improvements and renters pay utility bills, many rental properties remain woefully energy inefficient.  The burden of high utility bills then falls on those least able to pay them. The purpose of this project is to develop and test a new approach, “TrashWall” in which a temporary interior insulating envelope is built within the existing exterior wall of a rented residential building.  In order to keep initial costs as low as possible, this interior wall is fabricated primarily of materials harvested from the local solid waste stream such as scrap cloth, paper, corrugated cardboard, and polystyrene.  By keeping the cost of each TrashWall below ten cents per square foot, the payback period from energy savings in utility bills due to each TrashWall should be 200 days or less, or less than one heating season.

Summary/Accomplishments (Outputs/Outcomes):

Our interdisciplinary team has been successful in completing two design and build iterations of TrashWall concepts. In the first iteration, the team designed and built four TrashWall prototypes, including one 4 foot wide x 8 foot high TrashWall prototype assembled from four shopping bag quilts. These quilts were manufactured by rescuing polyethylene shopping bags from the waste stream, cutting the bags into square sheets, and heat welding them into square pockets, which were stuffed with shredded paper. Individual pockets were then heat welded together into large quilts which were layered together to form a thickness of approximately eight inches.  Material costs for this shopping bag quilt was thus zero ($0.0 per ft2).   Heat transfer measurements indicated an R-Value of RSI =1.3 m2 C/W (RUS = 7.3 hr ft2 F/Btu) for a four-layer, eight-inch thick quilt.

Interviews with the WSU Fire Marshal indicated serious fire safety concerns for a TrashWall manufactured from polyethylene sheet and shredded paper without any fire break. In addition, difficulties with manufacturing prototypes caused discussion about how fabrication might be streamlined.  As a result the student designers revisited their prototype design goals, and refocused their efforts to redesign TrashWall prototypes with an emphasis first on fire safety and second on design for manufacture and assembly (DFMA).  This resulted in a new iteration of TrashWall system design based into three complementary subsystems or functional components: a structural component or skeleton, an insulating component or filler, and an aesthetic facing component or skin.  Two new structural/skeleton concepts were developed, several insulation/filler options were investigated, and a large number of aesthetic/skin possibilities were designed. 

To address the requirement for fire safety, a number of aesthetic skins were designed specifically with this constraint as one of the primary considerations.  One skin option, taking the form of hexagonal tiles, fabricated out of paper and concrete in a paper mache like process, called “papercrete,” appears particularly promising.  The resulting tiles are very fire resistant, with tiles not igniting after 15 minutes exposure to the flame of a propane torch held to the tile.

To assess insulation/filler options, steady-state heat flow measurements were made on individual modules (individual units that are assembled together to build a structural skeleton) holding the three potential insulating fillers: shredded paper, commercial cellulose insulation, commercial fiberglass insulation., R-values for four inch thick modules were found to be 1.7 m2K/W (R10 US) for shredded paper, 2.2 m2K/W (R12 US) for commercial cellulose and 2.8 m2K/W (R16 US) for commercial fiberglass fillings.  

A complete 4 foot wide x 8 foot high TrashWall prototype was assembled from many individual shredded-paper-filled modules, with a material cost of $0.50/ft2. Hot Box measurements on this prototype indicated a disappointingly low R-Value of RSI =0.9 m2 C/W (RUS = 5.1 hr ft2 F/Btu).  This R-value, just over half of the R-value for an individual shredded-paper-filled module indicated a significant heat leak in the prototype. Rebuilding the prototype wall with attention focused on reducing air infiltration routes through the wall while maintaining uniformity in filling, and retesting the heat transfer rate through the rebuilt prototype wall indicated a new increased R-value of RSI =1.2 m2 C/W (RUS = 7.0 hr ft2 F/Btu).  This R-value for the rebuilt large-section prototype while higher than the previous iteration, is still 20% lower than the R-value found for an individual module.


Based on the results gathered to date, the TrashWall team has demonstrated that its internal envelope insulating walls fabricated from materials recycled from the waste stream could be built with measured R values of  RSI =1.2 m2 C/W (RUS = 7 hr ft2 F/Btu) for material costs below $0.10 per ft2.  

Creative use of materials by the student design team has led to very interesting and attractive wall treatments. With a focus on design for manufacture and assembly (DFMA) a second iteration of prototypes was designed based on a component subsystem approach. Each TrashWall system was broken down into a structural skeleton, insulating filler and aesthetic skin.  This new approach has led to TrashWalls that are much more flexible and can support a wider variety of insulating options and aesthetic finishes.  In addition, using a component approach with a focus on design for manufacture and assembly (DFMA) has led to prototypes that can be quickly and easily assembled from modular components.  Those modular components are in turn simpler and faster to manufacture. 

Fire safety concerns emerged as a significant issue midway through the project.  Fire safe options for all three components of the TrashWall system have been identified. However, greater fire safety appears to come at a trade-off of greater cost. First, both the structural skeleton and the aesthetic skin can be made significantly more fire resistance by the incorporation of “papercrete,” a combination of both cellulose fibers and concrete. Second, the fire safety of insulating filler can be increased through the use of either commercially available cellulose insulation or fiberglass insulation.  The incorporation of any or any combination of these three options will necessarily trade greater installed cost for greater fire safety.

Based on work that has been completed, and TrashWall prototypes built and tested, it appears safe to say that it is possible to fabricate an interior insulating wall with a measured R-value of at least 1.2 m2K/W or R7 US, built almost entirely from recycled materials harvested from the waste stream at an installed cost of less than $0.10/ft2 of wall. Such an installation would consist of the four-inch thick cardboard structure filled with shredded paper insulation filler and faced with 1/8” thick papercrete tiles for fire resistance tested in Phase I of this project.    Installed in a rental unit with walls with effective R-value of R = 1.5 m2K/W or R9 US and situated in a climate like Pullman, WA, typical for the Intermountain West, such a TrashWall would save the renter 9 Whr per day per ft2 of wall leading to a utility bill savings of 0.12 cents per day per ft2 of wall.  These savings would lead to a payback period for the installed TrashWall of 80 days or just under 3 months.  

For comparison, it would be possible to increase the fire resistance of the TrashWall by shifting from shredded paper to fiberglass insulation which would significantly increase the cost of the TrashWall from $0.10/ft2 to 0.30 $/ft2.  This higher cost would lead to the much longer payback period of 175 days. The payback period would then stretch out to almost 6 months or about one heating season.

This project has contributed to the goal of pollution prevention in two major and complementary ways.  First, the project addressed the prevention of solid pollution by reducing the amount of solid waste being disposed of. We reduce the disposal of solid waste, by reusing locally-harvested, waste materials as building materials for our energy saving TrashWalls. This supports the EPA’s mission under SWDA: Solid Waste Disposal Act--Section 8001: by contributing to resource recovery and conservation, production of usable forms of recovered resources; and waste reduction.  Second, the project addressed the prevention of air pollution, by reducing combustion gases, including greenhouse gases that result from the burning of fossil fuels. We worked to reduce the production of combustion gases, by designing insulating TrashWalls that will reduce the energy needed to space condition the residential buildings they are installed in. This supports the EPA’s mission under CAA: Clean Air Act--Section 103, by preventing air pollution, particularly from utility electrical production and from the burning of fuels (such as natural gas) for space heating. Finally, our work has focused on developing an approach that lends itself to “Do-It-Yourself” (DIY) solutions that empower and encourage community members to save energy and prevent pollution, by designing and building TrashWalls in their own dwellings, wherever they live.

In summary, the prototype TrashWalls under development in this project utilize recycled materials that would have entered landfills, and have the capability to reduce greenhouse gases associated with the combustion of fossil fuels: either through reduced utility-generated electrical power use or reduced natural gas or heating oil use.  Beyond these cost and energy savings, TrashWalls could enhance the lives of low-income renters by enhancing their living spaces. Those renters employing TrashWall solutions would experience much reduced drafts and a higher mean radiant temperature leading to greater comfort in their residence.  The renter would also have claimed greater control over their own lives and the ability to enhance their own living space.

Supplemental Keywords:

Building energy conservation, green building, sustainable infrastructure design, design for the environment, energy conservation for the poor

Relevant Websites:

Washington State University TrashWall