1. INTRODUCTION TO WARM AND DRYWALL
This chapter describes the methodology used in EPA’s Waste Reduction Model (WARM) to estimate streamlined life‐cycle greenhouse gas (GHG) emission factors for drywall beginning at the waste generation reference point. 1 The WARM GHG emission factors are used to compare the net emissions associated with drywall in the following three waste management alternatives: source reduction, recycling and landfilling. Exhibit 1 shows the general outline of materials management pathways for drywall in WARM. For background information on the general purpose and function of WARM emission factors, see the Introduction & Overview chapter. For more information on Source Reduction, Recycling and Landfilling, see the chapters devoted to those processes. WARM also allows users to calculate results in terms of energy, rather than GHGs. The energy results are calculated using the same methodology described here but with slight adjustments, as explained in the Energy Impacts chapter.
Exhibit 1: Life Cycle of Drywall in WARM
Raw Material & Intermediate Product Acquisition, Processing, & Transport (Virgin Manufacture Only)Raw Material Acquisition, Processing, & Transport (Virgin Manufacture Only)
Transport to Retail Facility
Drywall Manufacture: Recycling Offsets Virgin Manufacture
19% of recycled drywall to closed loop recycling
Transport to Manufacturing or Packaging Facility
81% of recycled drywall to open loop recycling
Agric. Gypsum Production: Recycling Offsets Virgin ManufactureTransport to Farm
Product Use Product Use
WARM Starts Here
Only Scrap from Construction Sites
Collection/Transport to Recycling Facility
Recycled Drywall Grinding & Paper Screening
Life‐Cycle Stages That Are GHG Sources (Positive Emissions) Life‐Cycle Stages That Result in Both Positive and Negative EmissionsSteps Not Included in WARM
End‐of‐Life Pathways in WARM Not Modeled for This Material
All End of Life Drywall
Extraction/Transport to Landfill
Only Installed Drywall
End of Life
Drywall, also known as wallboard, gypsum board or plaster board, is manufactured from gypsum plaster and a paper covering. Exhibit 2 presents the sources of drywall entering the waste stream.
EPA would like to thank Rik Master of USG Corporation for his efforts at improving these estimates.
Exhibit 2: Composition of the Drywall Waste Stream
Source of Waste Drywall New Construction Demolition Manufacturing Renovation Source: CIWMB (2009b). % of Total 64% 14% 12% 10%
There are several different types of drywall products, including fire‐resistant types (generally known as Type X drywall), water‐resistant types and others. Additionally, drywall can be produced in a range of thicknesses. Our analysis examines the life‐cycle emissions of the most common type of drywall, half‐inch‐thick regular gypsum board. Most drywall is currently disposed of in landfills (Master, 2009). This disposal pathway can be problematic; if water is admitted to the landfill, under certain conditions the drywall may produce hydrogen sulfide gas. Incineration can produce sulfur dioxide gas, and is banned in some states (CIWMB, 2009b). Drywall is sometimes accepted at composting facilities, but it is used as an additive to compost, rather than a true compost input (please see section 4.3). For this reason, WARM does not include a composting emission factor for drywall. However, users interested in the GHG implications of sending drywall to a composting facility can use the recycling factor as a proxy (again, see section 4.3). ...