Healthy homes improves quality of life.
By Natalie Leonard
Climate change is influencing how we build, and the demand for high-performance homes continues to grow. More clients and builders are moving toward both the Net-Zero and Passive House standards.
Passive House is a leading energy efficiency standard with its roots in Germany. This design standard focuses on conserving energy by using highly insulated assemblies that are six times more airtight than code-built construction. Passive House strategies are simple and focus on significantly reducing heating and cooling loads by using thick, air-tight assemblies.
Net-Zero homes use renewable systems – like solar panels – that generate enough electricity to supply each home’s own annual energy demand. Since it’s cheaper to reduce energy use than to generate it, Net-Zero homes also use thick, well-insulated, airtight exterior assemblies.
Thick, airtight assemblies have a higher risk of moisture build up. If the assemblies are not designed properly this can lead to mildew, mold and rot. Moisture can easily move into wall assemblies with air leakage and vapour drive. Although drying is slow in thick assemblies and moisture can build up over time, this risk is not a reason to avoid building thick assemblies – designed properly, they will perform better than code-built assemblies and be more durable over time.
These high-performance building standards don’t just contribute to fighting the climate crisis – they also prioritize healthy interior spaces that improve quality of life by eliminating mold and mildew, while providing a constant supply of indoor fresh air. Achieving this in a high-performance home requires attention to the moisture profile of the exterior assemblies, careful choice of materials, and a good ventilation system.
Guidelines for well-designed, high performance wall assemblies
Design for your climate. Don’t borrow assemblies used in other climates, as they may behave differently than intended. You can ensure the vapour control layer is on the warm side of the insulation. Do not build a vapour sandwich (where moisture becomes trapped with no path to drying). You should also avoid high-VOC-content (volatile organic compound) materials on the interior of the vapour control layer.
Carefully think through all air sealing details to be durable during construction and occupancy. A well-designed ventilation system will help remove VOCs from the home, but the best way to avoid off-gassing from these unhealthy chemicals is to build using low VOC materials. Many options are now readily available including paints, flooring and cabinetry materials.
A high-efficiency, balanced ventilation system is critical for good indoor air quality. Humans breathe through our lungs, not through our skin – our homes should be the same, so we want to avoid random air leakage through the building envelope, and to let our mechanical systems do the work. A good heat recovery ventilator (HRV) will exhaust stale air and supply fresh air efficiently by transferring heat from the exhaust to the supply air.
Guidelines for a high-performance ventilation system
Using a high efficiency HRV with ECM motors will save energy. Upgrade the filters to MERV 13, which will filter out dust and pollutants. Install and balance exhausts to kitchen and baths and supply ducts to all living spaces. Insulating, and air sealing a vapour barrier on all exterior ducts. Set the HRV to provide adequate air flow – too high a flow rate is unnecessary and only wastes energy.
Don’t install any bathroom fans, rangehood or dryer exhausts that vent directly to the outdoors. These will depressurize an airtight house and pull air, moisture, and pollutants such as radon, if present, through the assemblies.
Design operating windows for natural ventilation in the summer and shoulder seasons. A well-designed and carefully constructed high-performance home will be a healthy home. In addition to superior air quality, these homes are quiet, more resilient in storms and cost very little to operate, allowing residents to save money while feeling safe, secure and healthy.
Natalie Leonard is an Engineer and founder of Passive House.