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Tight building envelope4/15/2023 You can read more about these Net Zero Energy ideas in the article entitled “ Twelve Steps to Affordable Zero Energy Home Construction ” which was the inspiration for this post. Using either an HRV (heat recovery ventilation) or ERV (energy recovery ventilation) system will help keep the air moving to prevent mold and assist with moisture management. Using a high performance vapor barrier will ensure moisture does not get into the wall assembly. If the building is airtight, it is especially important to keep indoor humidity to less than 30% or less to avoid condensation. Yet, it’s just as important to use the largest roof overhangs to make the most out of the winter sun and avoid the summer sun. Using a solar heating system for hot water and heat is an obvious design decision. The frame allows more heat transfer than the window glass. Large windows have a higher glass to frame ratio. Finally, use fewer large windows over more small windows. Bear in mind that sliders and double-hung windows both have leak issues. Of course, depending on the climate at the building site, double panes may suffice if the U-value is also. In any event, choose triple-pane windows with a U-value of. Whether or not it is cost-effective to have 50% of the windows on the south side for any given location is a decision to address during the project’s design phase. Also, strive for a 6% window-to-floor ratio for maximum solar gain. It’s important to have 50% of the windows on the south side of the building which should house the common living area. The make-up of the windows and their placement is critical to a net zero building. It’s especially important to design decks and patios that are separate from the building so there is no heat loss between the building and the deck/patio. Use the Thermal Bridging Checklist to help design and build with minimum reduction in the building’s R-value. Where possible, identify and eliminate thermal bridges because trying to fix it with gels or foams is not as cost-effective as avoiding them in the building’s design. If you’re building in a northern climate, use dense fiberglass or cellulose to an R-50 rating in the walls and blow loose insulation to R-60 for the ceiling. It also helps to use raised-heel trusses for insulation in the ceiling. This will help keep out the cold in northern climates. Double 2×4″ walls with off-set studs set at 24″ and set 5″ apart will help form a wall cavity that is a full foot thick. Use modern framing techniques that save wood and allow space for insulation. Obsessing about testing and re-testing will provide rewards in a tighter seal. After sealing the discovered leaks, make sure to test again using the smoke stick. Use a smoke stick while the blower door runs. You can accomplish the exterior seal using glue, caulk, foam, or other air sealing products. Then, seal the exterior sheathing and the drywall ceiling before installing the drywall. Next, tighten the joints with mechanical devices rather than by hand. Use an Energy Star Thermal Bypass Inspection Checklist that can help identify areas that need sealing. Depending on the climate the air tightness standard is between 1.5 and 2.0 Air Changes per Hour (ACH).įirst, make sure that the exterior sheathing does not have any unintended gaps. It is important to create a tight building envelope around all six sides of a building (all four walls, the basement, and the roof). There are a number of things you can do when designing and constructing a building to improve building envelope energy efficiency.
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