7 Tips For Multi-Family Blower Door Testing

Date Published: October 14, 2019

Multi-family blower door testing is consistently becoming more common in all Colorado counties. Just as with a regular single family home, a multi-unit building will also need to have each unit pass a blower door test. This is typically required regardless of whether you are building a duplex or a 40-unit apartment building.

On top of that, the smaller the unit square footage is in an apartment building, the more difficult the test can be. Smaller footprints make achieving a 3ACH rating harder than a larger unit.

It is important for builders to think about their blower door testing requirements before construction starts. Once many of the air leaks are covered up with drywall, there is no way to seal them in a multi-unit building.

Because of this, we compiled some tips to help you with your next multi-family blower door test.

1. Exterior wall insulation:

We typically still see most builders using fiberglass batts during the construction of multi-family units. While this is a fine insulation product, it does very little to block air leakage.

We recommend using high-density blown-in products like cellulose in the walls. The packed insulation will provide a better air seal than batts. If possible, closed-cell foam is best, but this is a much more expensive product and is not always in the budget.Multi-Family Blower Door Test air leaks in walls
In this picture, you can see that air is moving through the wall cavities and in through the outlets and bottom edge.

2. Insulation between floors:

Between the drywalled ceiling of one unit and the floor of the above unit, the rim joists that meet the exterior walls and party walls should be sealed as tightly as possible. This is a commonly overlooked area as insulation is not typically required on the rim joists on large buildings.

However, the exterior wall coverings and wrap cannot stop all the air from getting into these floor joists. If not stopped, air typically will flow into the walls and through ceiling penetrations.

Many builders will spray-foam this section, which reduces exterior air moving through the floor cavities.

Be sure that you consider this when framing, because once the drywall is up, there is very little you can do about this large air leak.

Are you in need of a blower door test for your construction project in Colorado? Learn more about our services here!

3. House wraps:

Typically, house wrap is required on the exterior of the framing in Colorado, but not all wraps are created equal!

Plastic wrap on the exterior of the home can create a nice air barrier but non-ridged systems can rip, tear and be sealed incorrectly.

Consider using an exterior sheathing that claims to be a ridged air barrier such as Zip Wall System.

We have seen great improvements in homes that use this system top to bottom on the exterior of the home. This typically performs better than a Tyvek wrap.

4. Party Wall Mitigation:

Between units, a party wall with an air gap in between is required to prevent fires from spreading between units quickly. This is an important construction technique for fire safety, but can significantly contribute to air leakage.

Because the party wall runs the height of the building, the wall cavity is typically open at the top of the wall in the attic or elsewhere. This creates a large cavity for air to move from the vented attic, and into the unit through outlets, baseboard gaps and more.

See the image below for a visual representation of the top of the party wall.

These areas are usually insulated, but that often does not do enough to stop the air from entering the unit.

Sealing the top of the party wall with spray foam insulation will greatly reduce air flow between