The following information and examples provided are based on a typical NYC townhouse of a rowhouse typology.
PASSIVE HOUSE KEY COMPONENTS
Now you know Why You Should Build a Passive House, but what makes it a Passive House? These are the crucial components:
- Continuous air-sealing
- Reduced thermal bridging
- Air-tight & insulated windows
- Vapor control
- Energy Recovery Ventilators (ERVs) that continuously filter air & regulate moisture
PASSIVE COMPONENT: BETTER INSULATION
A Passive building’s insulation:
- Requires a higher R‑value than typical homes.
- Is continuous on all faces of the building.
- During warm months, the insulation layer blocks heat before it enters the envelope.
- During cold months, heat loss is reduced to the point of not needing to turn on the heat for most of the season.
Left: Insulation installed under the concrete cellar slab.
Center: Outboard (exterior) insulation at the roof.
Right: Spray-applied Rockwool, R-4 per inch. (Photo: American Rockwool)
PASSIVE COMPONENT: AIR SEALING
The building envelope is a continuous air barrier that controls infiltration and exfiltration.
Key factors for a successful air barrier:
- All joints and penetrations must be sealed.
- In masonry construction, the air barrier is liquid-applied to the masonry.
- Air-tight window connections are crucial.
- Essential to coordinate with the structural, mechanical, and electrical scope to eliminate gaps in the air barrier and seal the necessary penetrations.
PASSIVE COMPONENT: REDUCED THERMAL BRIDGING
Thermal bridging: when a higher thermal conductivity transfers heat to another material. Continuous insulation between materials prevents this heat transfer.
For exterior wall strategies, a continuous layer of insulation can create a virtually thermal bridge-free envelope. In rowhouses, typically where the historic fabric of facades is important, interior strategies with careful detailing must be used at fenestrations and intersections.
Thermal images displaying winter surface temperatures. Much of the interior heat is lost through thermal bridging and a lack of insulation at the facade.
PASSIVE COMPONENT: PASSIVE WINDOWS
- Triple-paned and insulated.
- Completely air-tight.
- Can cost the same as typical windows.
- Can be visually indistinguishable from historic windows, and can be Landmark/Historic District approved.
- Installation is easier than typical windows.
Left: typical windows, NYC Landmarks approved.
Right: Passive windows, NYC Landmarks approved. (Peter Peirce Photography)
Passive windows installed in NYC Landmark Districts.
Left, Center: Peter Peirce Photography
Right: Adam Macchia Photography
PASSIVE COMPONENT: VAPOR CONTROL
In a continuous, highly-insulated envelope, controlling vapor is necessary.
- Low heat loss in a highly-insulated system leads to an increased risk of condensation.
- Smart membranes react to cold & water cycles at a molecular level. They allow moisture migration without getting trapped in a wall cavity, thus reducing condensation and mold as it blocks unwanted air infiltration.
- Vapor-permeable insulation is moisture-resistant and vapor-open to allow for moisture migration.
- The result is a wall assembly that is air-tight, but allows natural moisture movement.
Smart membrane installed with seams taped.
PASSIVE COMPONENT: CONTROLLED AIR EXCHANGE
In a continuous, highly-insulated envelope, filtering air is necessary.
- “A leaky house is a fresh house” is over. A Passive house’s incoming air is filtered through the ERV (energy recovery ventilator), rather than through dirty wall assemblies.
- There is continuous air exchange through ERV system, providing fresh air & controlled humidity to all primary living spaces.
- ERV is independent of the heating/cooling system.
- ERVs extract air from wet & “dirty” locations (kitchens, bathrooms, laundry, mechanical rooms.)
- There is a boost mode when a bathroom is in use and for large gatherings.
- Users can still open windows.
Left: Typical ERV (Zehnder shown)
Center: ERV manifolds
Right: Visually minimal wall/ceiling grilles & diffusers available.