What is a Passive House?

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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:

  • Hyper-insulated.
  • 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.
<p><em>Left: Insulation installed under the concrete cellar slab.</em><br /></p>
<p><em>Center: Outboard (exterior) insulation at the roof.<br /></em></p>
<p><em>Right: Spray-applied Rockwool, R-4 per inch. (Photo: American Rockwool)<br /></em></p>

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.

<p><em>Thermal images displaying winter surface temperatures. Much of the interior heat is lost through thermal bridging and a lack of insulation at the facade.</em></p>

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

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.
<p><em>Left: typical windows, NYC Landmarks approved.</em><em><br /><em>Right: Passive windows, NYC Landmarks approved. (Peter Peirce Photography)</em><br /><br /><br /></em></p>

Left: typical windows, NYC Landmarks approved.
Right: Passive windows, NYC Landmarks approved. (Peter Peirce Photography)


<p><em>Passive windows installed in NYC Landmark Districts.</em></p>
<p><em>Left, Center: Peter Peirce Photography</em></p>
<p><em>Right: Adam Macchia Photography<br /></em></p>

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.
<p><em>Smart membrane installed with seams taped.</em></p>

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.
<p><em>Left: Typical ERV (Zehnder shown)</em><br /></p>
<p><em>Center: ERV manifolds<br /></em></p>
<p><em>Right: Visually minimal wall/ceiling grilles & diffusers available.<br /></em></p>

Left: Typical ERV (Zehnder shown)

Center: ERV manifolds

Right: Visually minimal wall/ceiling grilles & diffusers available.

Author

Baxt Ingui Architects
Baxt Ingui Architects
Baxt Ingui Architects has completed seven certified Passive House residential projects, one of which is LEED Platinum and several of which…