During new construction or remodeling you have to opportunity to seal the exterior shell of the home to reduce air infiltration.
This helps improve air quality by sealing out pollution and allergens, and it makes the home more energy efficient.
On the outside of a house it’s common practice to install HOUSE WRAP.
House wrap helps cover gaps in the framing of a house, to keep air from freely blowing in.
House wrap will also shed water, meaning that if water penetrates behind the house’s siding or stucco it will drain down the face of the house wrap, staying on the outside of the house.
Some new house wraps even have a slightly crinkled surface.
This creates little grooves for the trapped water to travel down through.
But house wrap is a “breathable” membrane.
This means that air and humidity can pass through it, slowly.
The benefit of a breathable membrane (vs an “impermeable” membrane, such as a sheet of plastic) is that if moisture or humidity somehow get inside the wall, it’s not trapped in there, where it could cause mold or rot.
The moisture has a way to slowly “dry to the outside.”
You apply house wrap before windows, doors or siding.
Generally you staple it on, and seal the joints with a plastic tape.
During new construction or remodeling, when the framing is still exposed, you also have the opportunity to seal the shell of the house from the INSIDE.
Air sealing is done before any insulation is installed.
For DIYers, a spray foam sealant (“Great Stuff” is a common brand) usually works best.
Seal the thin gap between window and door units.
Use a “minimally expanding” foam around windows and doors.
Regular foam might expand so
much that it bows the window or door jambs.
Seal around any penetrations in the exterior wall sheathing (such as around electrical boxes).
Seal any place where a cable or pipe passes through the bottom or top plate of a wall.
This is especially important on the top plates of any walls that have unheated attic spaces above them.
Make sure to seal penetrations in top and bottom plates for ALL walls.
Building inspectors will insist on this for “fire blocking” reasons.
In this case, you want to make it difficult for a fire in stud cavity to spread to the area it wall through small openings in the top plate.
Professional insulators have special products and equipment available to them to do a much more thorough job than do-it-yourselfers in sealing up homes.
One of these, the “Energy Complete” system, uses a latex-based spray sealant to seal many of the crucial weak spots on the shell of a building.
It is sprayed wherever there is a gap — between the top and bottom plates and the wall sheathing, at joints between pieces of wall sheathing, at any penetrations of the shell for wires or cables, and all of the usual spots for sealing, including cable and pipe penetrations in the top and bottom plates.