Earlier in the week, we discussed the Harvard TH Chan School of Public Health’s 9 Foundations for a Healthy Building.
When building to minimum building code standards, these items do not seem connected because the building is not designed as a system as much as it is designed as a collection of parts. Building codes are minimum standards that aim to ensure health and safety concerns are less of a concern for consumers. In high-performance building, such as passive building, a lot of these items piggy-back on each other. For example, proper ventilation and thermal control tend to improve air quality while reducing moisture, dust mites, and pests. Thermal control also generally improves acoustical comfort. PHIUS+ certification specifies continuous insulation, airtight construction, and proper ventilation using small and quiet mechanical systems and great windows. Other aspects on the list of nine—which affect indoor environmental quality, but which are not required for PHIUS+ certification (daylighting, acoustical comfort)—are often part of the PHIUS+ package because that is just good design, and PHIUS buildings are designed by people who give a damn.
The five PHIUS+ principles:
1/ Continuous insulation
By completely wrapping a building with insulation, heat can no longer sneak out through framing, which has a lower R-value than the surrounding insulation. The simplest way to fix all of those energy sieves is to avoid building them in the first place. Continuous, thick, insulation on the outside of a building keeps heat flow to a minimum.
2/ Airtight construction
While thick, continuous insulation can stop a significant amount of heat loss through conduction, plugging air leaks can slow heat flow, too. Because temperature drives air movement—think about convection loops—the air moving through buildings usually carries a lot of heat with it. So here’s the rub: Warm air can hold more moisture than cold air. So when warm air leaks through electrical outlets into exterior walls, it dumps moisture into wall cavities when the moist air hits the cold wall sheathing. It happens in winter and summer, only in reverse.
Sound waves also travel on air currents and through framing members, so these first two principles have the added effect of better sound control.
3/ Optimized windows
The appropriate window depends on your climate zone; cold climates need well-insulated windows because the temperature extremes are significant. Hot-climate windows typically have strong radiant-heat blockage because the sun is intense in hot climates. Another aspect of windows is shading, which can reduce glare and overheating, and is often cheaper that additional window technology. Regardless of climate or wall elevation, very good double-pane and triple-pane windows which are designed to be airtight are great from an acoustical perspective, they tend to be super quiet.
4/ Balanced ventilation
Air-tightening means that dirty, moist air isn’t leaking into the living space from basements and loading docks, which is good. It also means that stale indoor air is not leaking out, which is bad, so air changes must be controlled with some sort of high-tech fan. With balanced ventilation and a tight envelope, a constant flow of fresh air flushes the living space and conditions it to be perfect for human comfort.
Ventilator filter required min Merv 7, highly recommended to be MERV 13
5/ Minimal mechanical system
Because the building is super-tight, super insulated, and has super windows, a super-size heating and cooling system is unnecessary. A great side effect of minimal mechanical systems is that they are much more quiet.
When these five principles are applied to buildings, you get predictable performance, unmatched comfort, superb air quality, and resiliency in the face of power outages due to winter storms or summer blackouts. We can say that PHIUS+ is the most cost-effective path to the Harvard list of healthy building foundations because the core objectives of PHIUS+ address the concerns of healthy building. Healthy buildings are a byproduct of PHIUS+ certification.
Best of all, because PHIUS+ buildings consume so little energy, zero energy is easily within reach.