Construction, demolition, and renovation (CRD) wood waste represents a significant proportion of Canadian waste. Nationally, 10% of all residual solid waste and 40% of CRD waste is wood.[1] Our ability to successfully reuse and recycle wood materials is dependent on our ability to extract those materials from the built environment at the end of a building’s useful lifespan. Typical construction does not allow for easy material salvage as non-reversible connections and adhered layers (such as self-adhered membranes, adhesives, and sprayed insulation) prevents easy deconstruction and material salvage.
This project expands on our previous work in design-for-deconstruction for light wood frame. The previous research included the development of a mock-up wall section constructed using design-for-deconstruction principles. This mock-up was subsequently deconstructed to test the ease of disassembly and the quality of materials salvaged from the deconstruction. This phase of research also produced assembly details of that mock-up and a number of other potential configurations that would allow for a variety of insulative values. The constructed mock-up was designed with an R-22 effective insulation factor to conform with the recommended requirements established by the city of Vancouver.[2]
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Principles of Design for Deconstruction
The Canadian government developed a Guide for Design for Disassembly (CSA Z782-06) which sets out general guidelines for designing for deconstruction and disassembly. The Guidebook of DfD in Light Wood Frame Constructions aims to apply those principles to typical light wood frame construction and provide detailed examples of construction solutions that allow for deconstruction. The examples provided in the Guidebook are not comprehensive but illustrate the minimums of performance requirements and show specific alterations to light-wood frame construction to allow for deconstruction. These alterations are generic enough to applied to a variety of building typologies and are applicable wherever light-wood frame construction is specified.
The modification of the light-wood frame construction are as follows: Replace nailed connections with screwed connections or double-headed nails to allow for disassembly, omit any plastics or adhesives from the assembly and use wood fiber insulation for exterior insulation and vapour-open batt insulation to allow for a breathable but air-tight building envelope, and optionally, use cladding and interior finishes that can be removed and replaced to allow for simplified repairs and access to the service cavity. For additional air-sealing, the exterior joints of the sheathing panels and interior edges of windows and doors are sealed with flashing tape.
While it is presently uncommon for screws to be used in the construction of shear walls, research by FPInnovations does provide engineering design guidelines for the seismic force modification factor and inter-storey drift required for sound shear-wall construction using screws.[3] The BC Building Code (section 9.23.3) also provides sizing and spacing recommendations for the structural use of wood screws. Double headed nails may also be used for framing connections, however, as found during the first mock-up assembly, when attaching sheathing panels double-headed nails make installing exterior insulation difficult. The modifications of typical light-wood frame construction proposed by the initial research do not alter the structure or construction order used in typical construction practices which would allow for a simple modification of building practice. The assembly details for a typical wall assembly are fully resolved and the remaining detailing work will apply these same design-for-deconstruction principles to other assemblies.
[1] Environment and Climate Change Canada, National Waste Characterization Report : the Composition of Canadian Residual Municipal Solid Waste, research report no. 9780660341569, 30-31, 2020, accessed May 6, 2024, https://publications.gc.ca/site/eng/9.884760/publication.html.
[2] City of Vancouver, R22+ Effective Walls in Residential Construction in British Columbia, 6, accessed May 3, 2023, https://vancouver.ca/files/cov/ig-r22-effective-walls-residential-construction.pdf.
[3] Chun Ni, Performance of Shear Walls with Wood Screws Under Lateral Loads, research report no. W-3071, 17, March 2014, accessed May 3, 2023,https://library.fpinnovations.ca/en/viewer?file=%2fmedia%2fWP%2f3071.pdf#phrase=false&pagemode=bookmarks.