Air sealing detail

The Western Sullivan Public Library – Jeffersonville Branch is a good example of a partial retrofit that was very impactful. The thermal envelope was enlarged to include the entire attic, i.e., the insulation was moved from the attic floor to the roof rafters.

The first step in insulating the roof rafters is the installation of an air barrier fabric. Cellulose insulation is then “dense packed” into the space created by the air barrier and attic roof slope. Rigid insulation was then added to the exterior roof before the existing metal roof material was reinstalled. This creates a continuous insulation to reduce loss of heat through thermal bridging.

The blower door test showed a reduction of 10 air changes per hour (15ACH50 reduced to 5ACH50).

This work was done in the winter, after the air barrier was installed and taped—but before dense pack insulation was put in place, staff had been shutting off supplemental electrical heaters at their desks.

The photo shows the attic with the air barrier installed. The bulges in the barrier are created by the densely packed cellulose. All seams are taped to keep the air barrier continuous.

A house that performs: Passively

Passive building comprises a set of design principles used to attain a quantifiable and rigorous level of energy efficiency within a specific quantifiable comfort level. The principles optimize the gains and losses based on the locale’s climate. To that end, a passive house or building is designed and built in accordance with these five building-science principles:

1. Employs continuous insulation throughout its entire envelope without any thermal bridging. What this means is that the building is extremely airtight, preventing infiltration of outside air and loss of conditioned air.
2. Employs high-performance windows (double or triple-paned windows depending on climate and building type) and doors. Solar gain is managed to exploit the sun’s energy for heating purposes in the heating season and to minimize overheating during the cooling season.
3. Uses some form of balanced heat- and moisture-recovery ventilation.
4. Uses a minimal space conditioning system.

Passive building principles can be applied to all building typologies—from single-family homes to multifamily apartment buildings, offices and skyscrapers.

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