The contemporary best practice is expanding spray foam insulation installation. Foam fills the cavities in between the framing studs of the walls and attic. Spray-on foam expands to fills in air gaps, unlike standard fiberglass insulation, which lets air pass through and around it. Even as a house expands and contracts the foam insulation expands and compresses with it. This prevents warm air from escaping through cracks and spaces.

A professional installer has the equipment to cover large areas quickly so that it is more cost effective than doing it yourself, but for small areas and sealing cracks you may choose to do it yourself. For a large space being installed with expanding spray foam insulation, the liquid to sprayed evenly between studs on the inside of the exterior sheathing. The material quickly expands 100 times its volume to fill all the gaps in the stud wall or rafter space. After the foam has set a handsaw is used to smooth off the excess from the framing. The wall or ceiling is now ready for drywall installation.

A better air-tight envelope is achieved by using expanding spray foam insulation in the walls and attic. The foam is non-toxic, high R-value, moisture-proof, fire resistant, and sound damping.