Home Attic Insulation

Attic insulation can provide huge energy savings. In colder climates, quadruplicating a low attic insulation (say, three inches) may save up to 20% in heating costs.

attic insulation Cost

Attic insulation costs depend on the amount and type of insulation, the size of the attic, etc. Insulation costs between $300 and $600 are common.

Insulation Materials

If you intend to use loose-fill materials, it’s better to hire a professional to install the attic insulation.

Fiberglass is the most common and cheap insulating material, but cellulose and mineral wool are good alternatives for attics. Cellulose is a truly 'green' insulator, with a high thermal and acoustical performance. Most attics use...

1- Loose-fill fiberglass, cellulose or rock wool.
2- Batts/rolls (fiberglass, cellulose and rock wool).

Batts and rolls are slightly more expensive than loose-fill insulation.

See for details:

Cellulose insulation
Fiberglass and mineral wool insulation
Reflective insulation: Radiant barriers

Recommended R-values

Attics and roofs with cathedral ceilings demand higher R-values than walls. Recommended R-values vary with climate. A rough rule of thumb states the following values:

- Hot climates: R-19 in ceilings below ventilated attics.
- Moderate climates: R-30 in ceilings below ventilated attics.
- Cold climates: R-39 to R-49 in ceilings below ventilated attics

Batt Installation

Avoid gaps and voids. Butt the ends of the batts together. In case of obstructions (plumbing stacks...) cut the butts and fit the material around them.

A proper batt installation involves filling the joist cavities completely, which demands a proper width of the batts. Small open spaces will cause lower performance. Batts should have the proper width. When buying, take into account the space between the floor joists.

If installing the batts or rolls over existing insulation, buy unfaced batts/rolls. Otherwise, buy faced batts/rolls and install the faced side down.

Loose-fill cellulose and fiberglass Installation

Installing loose-fill fiberglass or loose-fill cellulose or mineral wool in attics isn’t exactly difficult. But the installation is best done with a blowing machine, and demands a correct calculation of the number of bags and thickness to obtain the desired R-value. That's why hiring the services of a professional is desirable.

Note: Loose-fill insulation demands an additional piece of rigid foam board – or a similar material – on the top plate (at the outer edge) in order to prevent the insulation from being… blown.

Before the Insulation

There is a reasonable chance of existence of asbestos in old attics insulated with vermiculite and perlite materials. If this is your case, do not disturb the existing insulation, adding yourself a new one. Only certified contractors can handle and remove asbestos and deal with perlite and vermiculite insulation.

In other cases, before insulating your attic:

- repair roof leaks: check the attic ceiling for water signs, and make repairs before insulation.

- seal air leaks in the attic floor and around ducts and cover openings, or around the chimney and framings; also airseal the tops of interior walls or the attic access, if located in a conditioned part of the home.

Use resistant caulk to seal the smaller gaps and holes, and expanding foam or rigid foam insulation for the larger ones.

Attic Ventilation

Make sure the attic remains adequately ventilated. Insulation shouldn’t block soffit vents: they remove moisture in winter and excessive heat in summer, preventing overheating… Rafter gabbles are excellent to prevent it.

Do not forget to seal and insulate the attic vertical walls (knee walls).

Hot climates and reflective insulation

Attics and roofs in hot and mild climates may greatly benefit from reflective insulation and reflective roofing (use of membranes, coatings, ceramic light tiles, etc.)

See:
Reflective roofs
Reflective roof materials
Reflective insulation: Radiant barriers