Holistic Envelope Design
The key piece of the Net Zero puzzle is the building envelope—the shell of the house. High performance homes are better insulated and have Energy Star-rated windows to let the light shine in but keep the heat out in summer. Waterproof and airtight wall systems stop the outside elements from coming in and your heating and cooling from leaking out. Also the roof and foundation are thoroughly insulated and airtight.
High-Performance Exterior Walls Have Five Critical Barriers:
- Water shedding barrier
- Water resistant barrier
- Thermal control barrier (insulation)
- Vapour barrier, controlling the vapour movement through the wall
- Tape to seal the seam
Quik-Therm™
Quik-Therm is a composite structural insulation system that is attached to the outside of the wooden structure of the home. Thanks to tongue-and-groove connections it can be installed in about half the time than conventional insulation wall systems, saving material and labour cost.
Quik-Therm insulation has already proven its high performance and cost efficiency in Phase 1 of the Wilden Living Lab. Watch the video we took when Quik-Therm was installed in the Home of Tomorrow in 2016.
Foundation and Roof
Just as the walls, the roof, and the foundation of the home must be designed and built to keep the home temperature comfortable. The same barriers that apply to the walls are essential here. The layers should be breathable and airtight.
Radon Protection and Bottom Floor Insulation
Radon is a naturally occurring radioactive gas that tends to get trapped in buildings and may cause respiratory health issues after extreme exposure. The Next Generation Home features a Radon Guard layer under the concrete slab that allows for the collection of radon gas within the sub-slab space. The radon gas will be exhausted through a mitigation system and can not enter the building. At the same time Radon Guard is an insulating layer and is the code compliant replacement for a 100 mm thick layer of granular material.
Windows
A good window selection not only helps to keep the temperature in the house comfortable, but also the sound level. Traffic and other noises will be silenced by a well-insulated window.
Up to 25 % of energy loss in a home is caused by windows, doors and skylights. Energy Star rated windows are up to 55% more efficient than average windows. Their screens are designed to keep the cold air out and use the solar heat gain to help heat the home in winter. In summer over 70% of the solar heat gain is blocked to help keep the home cool.
The U-factor is the insulation value of a window. The lower the U-factor, the better the insulating properties. The U-factors in the Next Generation Home vary throughout the home, taking weather exposure and potential for solar gain into account.
Air Barriers
The air leakage rate of the Next Generation Home according to the blower door test is 0.57 air changes per hour. The minimum rate to achieve for a net zero home is 1 air change per hour. Every hour invested in the closing of gaps as well as taping and wrapping of the envelope will pay back in energy savings.
In this video Kyle from Kingdom Homes explains how to create a continuous air barrier in the framing stage.
Air Tightness
A Wilden Living Lab study compares two different investments in home insulation: sealing gaps where air leaks versus an upgraded wall assembly. The results were surprising: making sure the building envelope is properly sealed not only costs substantially less than upgrading your wall assembly, it also has a greater impact on reducing the home’s energy consumption.
Poor air tightness accounts for up to 40% of heat loss or heat gain in homes. Even if the envelope has the highest possible R-values, it will not work to its full potential if the shell of the home has a high air leakage rate (ACH – Air Changes per Hour). ACH is calculated by dividing the air flow from the outside per hour by the home’s volume. The minimum ACH currently required in British Columbia is 2.5. Step Code 5 requires an ACH of 1.
