ASHRAE Journal - January 2011 - 54

Solar NZEB ProjEct

Supersealing a House
I
By ty Newell, Member ASHRAE; and Ben Newell, Associate Member ASHRAE

n this column, we describe our efforts to superseal Equinox House. As

with our previous discussions on walls and windows, there is a point

at which too much effort and cost can occur. While there is information available in the general literature of the excellent sealing characteristics of structural insulated panels (SIPs), we found that these studies did not provide the basic information we were seeking to characterize the cost to seal the different features of our house. That is, what is the infiltration through the sill plate region, or the wall-to-wall panel joints, or the wall panel-to-roof panel joints, and similar building elements?

Supersealing a house is important for a number of reasons. First, energy and comfort are improved as a house is sealed. Second, deterioration of a structure by moisture movement through inf iltration paths to regions where condensation can occur is minimized if properly sealed. Third, the same infiltration paths where moisture may condense, forming molds and mildew, are the airflow paths that conventionally constructed homes rely on for “fresh air.” Fourth, these inf iltration paths are also used by insects and rodents to enter a home. By minimizing infiltration and using a controlled ventilation system, one gains the benefits of ventilating a residence at a proper rate (ASHRAE Standard 62.2), filtering the controlled ventilation air, which reduces the input of various allergens and dirt into the house, and performing beneficial energy exchanges between the fresh air and exhaust airstreams.

Our nominal goal was to seal Equinox House to a level achieving “Passive House” requirements of 0.6 ach at 50 Pa. The Passiv Haus Institut (www. passiv.de) bases this level of sealing as one in which infiltration is minimized to a point where controlled fresh air ventilation rates can be conditioned (heated or cooled) to a level matching the building’s load under most climatic conditions. The internal volume of Equinox House is 28,000 ft3 (790 m3), which is large for the size of the house due to nearly 20 ft (6.1 m) high ceilings. The high ceilings are a direct result of the SIPs construction, which eliminated the space normally occupied by roof trusses. Based on the size of Equinox House, a blower door flow rate less than 280 cfm (132 L/s) at 50 Pa is desired. To gain some perspective on the impact of this level of sealing relative to other building shell energy impacts, we can assess the overall heat transfer

Photo 1: Blower door in garage door. coefficient (UA value) for the primary house components. The SIPs walls and roof (approximately 4,800 ft2 [444 m2]) have a combined UA value of 50 W/K (95 Btu/h·°F). The windows have a total UA value of 26 W/K (49 Btu/h·°F). The three “double” doors have an estimated combined UA value of 2.5 W/K (4.7 Btu/h·°F). Finally, the ICF (insulated concrete form) foundation wall that extends 8 in. (0.2 m) above the concrete slab floor has an estimated UA value of 4 W/K (7.6 Btu/h·°F). The total of these parallel heat transfer paths through the building shell is 82.5 W/K (156 Btu/h·°F). Infiltration is an additional “parallel” load factor, and can be combined with the total UA value for the house. Formally, infiltration effects also add

this is the fifth in a series of columns. Find previous columns at www.ashrae.org/ashraejournal.
54 ASHRAE Journal ashrae.org January 2011

ASHRAE Journal - January 2011

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