PASSIVE HOUSE // A Brief Summary of the Approach
The Passive House approach is distinguished from both conventional and even high-performance building in a number of ways. The system is technical in its implementation, so in order to familiarize clients with Passive House, the benefits, diagnostics and verification measures that assure that the principles have been applied and performance goals met are outlined as follows:
Benefits of Passive House
COMFORT // Houses maintain a consistent interior air temperature across a room, regardless of orientation, so it is as comfortable to sit in front of a large window as it is deep inside a heated room on a cold winter day. Similarly, the capacity for the house to be decoupled from exterior surfaces means it maintains comfortable interior temperatures on hot days as well.
DURABILITY // Finishes and structures fail because of weak points in construction. The two categories that need to be addressed. Include (1) continuous assemblies and (2) assembly transitions. If continuous assemblies are robust, super-insulated, and effectively air-sealed, then it comes down to managing the transitions (foundation to framed wall, wall to roof, penetrations etc). Houses that foster infiltration allow moisture laden air to move through assemblies degrading the components, subjecting them to temperature swings and wetting/drying cycles. This shortens the life and performance of the material. By effectively eliminating moisture migration and air infiltration, this liability is eliminated. Temperature swings are minimized and materials remain stable and have longer service lives.
PERFORMANCE // By maintaining air tightness and ventilating with heat recovery, as much or more than 80% reduction in energy utilization can be expected. Indoor air quality is maximized.
The Passive House approach requires that performance be tested to verify air-tightness and identify areas that may have escaped scrutiny during construction. It isn’t just a matter of hoping it works, and verification assures that all trades have embraced and implemented the approach. Blower door and infra-red or smoke testing will reveal any weaknesses quickly in a pressurized/depressurized environment. Passive Houses must test to allow no more than 0.6 air changes per hour at a positive and negative pressure rating of (ACH)50 Pascals.
In contrast to conventional construction where infiltration is evenly distributed across foundation/framing, wall/roof and penetrations in a lower volume velocity, weak points in PH enclosures are subject to more vapor pressure as air seeks an entrance or exit point given difference in interior/exterior air characteristics. The result is higher acceleration and more moisture at weak points in the weather or air barrier, and accelerated failures. This is why diagnostics and verification are so vital and required.
With the benefits, diagnostics and verification aspects of the approach understood, we can articulate the basic principles that drive the approach.
- Thermal bridge free design: All components are designed and specified to limit the transmission of air/vapor through components and assemblies.
- Superior windows: Fenestration must be as or more robust than wall/floor/roof assemblies. Triple paned units with high quality glazing spacers, seals and hardware assure performance.
- Ventilation with heat recovery: Boosting the efficiency of the heating/cooling system, no energy is wasted from the recirculation of conditioned air. All air is filtered/exchanged with fresh incoming air, so heat and moisture are recovered before stale air is exhausted to the outside.
- Proper insulation: Performance requires robust levels of cellulose, mineral wool or similar insulations. Substitutes for rigid and sprayed foam are sought in all instances.
- Airtight construction: All of the above rely on the capacity for the interior air volume to not be compromised by infiltration.
Passive House is the pinnacle system that a building should embrace to build in the 21st Century. By adhering to the primal necessity to provide shelter (comfort), we execute a work that anticipates the effects of moisture and exposure (durability) while facing down the disproportionate share of greenhouse gases generated by buildings worldwide (performance) and valuing the natural resources we all treasure.