The objectives of this study were to de-risk investment in deep retrofits in Canada, to provide evidence on the effectiveness and scalability of a panelized deep retrofit approach and to build confidence and experience in deep retrofits among Canadian municipalities and industry stakeholders.
The goals for the Deep Retrofits explored included:
The Harrietsfield Williamswood Community Centre is a two-storey building with a gross floor area of 581m2 (6,256sq. ft).
The upper level of the building contains a day care centre which operates an after-school program and full day programs during summer and March Break. The facility includes a multipurpose room which is used for community recreation services including fitness classes, meetings, art classes and workshops and for private event rentals. Daily hours of operation are 10am – 9pm during the school year and 7:30am – 6:00pm in summer. The typical occupancy of the daycare is 50 people and occupancy of the multipurpose room varies, with an average of 150 people for events.
The building was originally a fire station estimated to have been constructed in 1970. It was converted to its current use in a major renovation in 1994. HRM has implemented several efficiency measures to the building including adding heat pumps (2015), LED lighting upgrades (since 2013) and a wall mounted solar air heater (2011).
The facility has been operated in partnership with the Harrietsfield Williamswood Community Centre Association (HWCCA) since 2010. Capital work on the building, including major repairs and maintenance of mechanical and electrical systems are the responsibility of HRM while utility costs are paid by the HWCCA.
The main walls of the building are concrete block with interior 2x6 stud cavity walls offset from the concrete 100mm (4”) and insulated with fiberglass batt. The lower-level bump out walls are 2x6 framing with fiberglass batt. Openings from three former overhead doors on the west wall have been infilled with wood framing and fiberglass batt. The building is clad with fiber cement siding, with a small area of brick framing the former door openings. The windows are double glazed with vinyl frames.
The roof is framed with wood trusses and insulated with approximately 200mm (8”) of loose cellulose at the ceiling plane. There appears to be a polyethylene vapour barrier installed in the walls and roof. Given the building’s age, this is unlikely to be continuous.
The concrete slab-on-grade floors are believed to be uninsulated.
The foundation consists of concrete foundation walls and strip footings. No structural deficiencies are apparent in visible portions of the foundation and there is no evidence to suggest deficiencies in the buried portions.
The above-grade walls are 150mm (6”) concrete masonry unit (CMU) block. These are the main load-bearing elements and the primary lateral load resisting system. The team was unable to confirm the presence of grout or steel reinforcing in the CMU voids. There is no evidence to suggest structural deficiencies in the wall system.
The roof structure is pre-engineered timber trusses with tongue and groove plank decking. The connection detail between the trusses and walls could not be verified during the site visit. It is assumed that the trusses bear on either a double top plate or a nailer on the CMU block walls.
The roof trusses are leaning, with the truss ridge approximately 25mm (1”) east relative to the bottom chord of the truss. This issue wasn’t identified in the 2013 Building Condition Assessment (Appendix B). A roof leak was also identified, by an employee of the daycare. This has anecdotally been present since Hurricane Dorian in September 2019.
The existing roof structure was determined to be inadequate to support existing loads. Alterations must be independent of the existing roof trusses.
The design team worked collaboratively to develop retrofit scenarios targeting the project objectives. The analysis assumes a ‘like for like’ retrofit where space usage, occupancy schedules, internal geometry, volume of conditioned space, and window and door dimensions and locations are consistent with existing conditions.
The strategy for building enclosure upgrades is to retrofit the walls with prefabricated ReCover panels and to increase the depth of cellulose insulation in the roof. The existing roof can hold a few more inches of cellulose insulation, however for net-zero performance a new roof with a raised heel truss is necessary since a panelized approach is not possible.
Building enclosure upgrades were developed for post-retrofit airtightness targeting 0.5 L/s·m2, a 75-80% reduction from the existing air infiltration. Upgrading to high performance windows was also included.
Mechanical and electrical retrofits were developed based on ease of integration with existing systems and installation cost. This involved the full electrification of the building’s mechanicals. As the building has a high occupant density, the heating and cooling systems were designed around the cooling loads. Each scenario includes the addition of high- performance ventilation.
Both air source heat pumps (ASHP) and ground source heat pumps (GSHP) were considered in the design analysis. A GSHP is more energy efficient than an ASHP, however the capital costs of installing a GSHP system are typically much higher. Depending on the specific building details it is not immediately apparent which option is the better investment. The Net Zero Energy scenario is based on the GSHP option which resulted in the lowest TCBO.
The prototype ReCover panel is a wood framed box which holds carbon storing cellulose insulation. The depth of the frame is flexible depending on the needed performance.
The panel components were specified to reduce moisture risks from both internal and external sources. Strapping on the back side of the panel allows for fitting adjustments and makes an internal air cavity and moisture buffer, allowing any vapour diffusion from the inside to move out through the panels. The rear panel layer is a “smart” vapour control membrane which varies in permeability, also to let vapour pass. Cellulose and wood are hygroscopic, transporting moisture to support drying activity. A vapour-open water-resistive barrier (WRB) protects the panel’s outer plywood sheathing. This acts as a drainage plane behind the rainscreen cavity and metal siding. Metal siding is recommended for longevity and durability.
PDF of Wall Panel Details | Sketchup File of Wall Panel Details
Embodied Carbon was modeled for this project in One Click LCA. Materials modeled were based on the most representative materials available to the Canadian market with Environmental Product Declarations (EPDs) available in the One Click LCA database. The analysis was limited to embodied carbon of assembly materials being added to the existing building including panel additions to above-grade walls, roofs, below-grade components, and windows and doors. HVAC and electrical components were excluded from the analysis.
The results include a whole life cycle assessment of the building in six impact categories: Global Warming, Ozone Depletion, Acidification, Eutrophication, Formation of tropospheric ozone, Depletion of nonrenewable energy, and Biogenic carbon storage.
Total Cost of Building Ownership (TCBO) analysis was conducted using the SEEFAR-Valuation© program. Calculations include costs for utilities, carbon tax, maintenance, maintenance capital (replacing major components as they age out), interest, and escalation of these costs over time. TCBO analysis typically includes property tax and insurance, however the building is not subject to property tax and insurance costs were not quantifiable as the building is covered through a blanket policy where costs for one specific building can’t be isolated.
The cumulative total cost of building ownership becomes cheaper than business as usual after 39 years.
