Air Sealing Tips and Tricks

Drywall corners can be sealed with caulk before application of corner bead and joint compound.

Depending on the situation, air-sealing can call for caulk, canned foam, tape, sheet material, or a combination of materials. The author’s jobsite arsenal covers all the bases.

High-performance bulk caulk, applied with refillable pneumatic caulking guns, is a useful alternative to canned foam for many applications.

If air-sealing is going to be done right, someone has to sweat the details. The author’s shirt leaves no doubt as to who that person is.

Small-diameter pipe penetrations through drywall or plywood are efficiently sealed with two short pieces of tape.

Larger pipes, like this rangehood exhaust vent, may require a dozen pieces or more.

Floor penetrations that will be enclosed in a partition wall are best sealed at the level of the subfloor, rather than where they pass through the plate.

In retrofit applications where that’s not an option, air leakage under the plate can be reduced by sealing the area with duct mastic.

Floor openings around bathtub P-traps can leak as much air as an open window. They’re best closed off with a piece of polystyrene — notched on one edge to fit around the pipe — set in a fresh bead of canned foam.

A small filler piece at the drainpipe is foamed in place to complete the seal.

Conventional plastic electrical boxes can be sealed to partitions by sticking a strip of tape against each of the inner walls of the box and folding the portion that extends beyond it against the drywall. The width of the flange has been sized to fit under a oversized outlet cover, or "goof plate." The manufactured airtight box below is easier to seal but expensive; for economy, the author uses this type of box mostly on outside walls.

Leaky metal boxes exposed in the course of a retrofit can be sealed to the back of the drywall with tape.

Leaky metal boxes exposed in the course of a retrofit can be sealed to the back of the drywall with tape.

Where a new metal box is called for, tape provides a more reliable seal around the cable than foam, which is prone to cracking when the electrician installs the fixture or receptacle.

A scrap of pre-drilled plywood or OSB can be used to create an air-sealing “sandwich” where closely spaced pipes or wires penetrate wall framing at a plate.

A strip of foil tape seals an air leak in an "airtight" ceiling can.

The much larger — and often overlooked — leak between the fixture and the ceiling drywall has been sealed with tape.

On a can with an integral trim ring that prevents the use of tape, a rolled "shoelace" of duct putty forms a seal.

Excess putty that squeezes out is removed later.

When wall sheathing is set in beads of polyurethane foam, temporary blocks at the base make it easier to position the sheet without smearing the sealant.

For extra insurance, seams between panels are also sealed with tape.

An intentional 1/4-inch gap below the drywall on exterior walls is easily filled with canned foam. In a retrofit project, it’s a good idea to protect the finish floor with paper or tape first.

Warm air venting from the attic above sucks a protective plastic sheet against this single-layer T&G ceiling, illustrating its extreme permeability to moving air.

To stop air penetration at the gable overhang of a T&G cathedral ceiling, a 3/4-inch bit is used to bore holes where the boards cross the outermost pair of rafters.

The holes are then injected with foam.

Plywood bedded in polyurethane foam seals air leaks between blocking and rafter tails. A stucco wall finish will cover the raw bottom edge of the plywood. A nearby rafter bay has been sealed with tape instead of foam — a time-consuming but more positive solution.

The excess foam that marks an injection hole for dense-pack cellulose will be trimmed off, and the tape covered with a plywood trim piece.

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