Home attic insulation and sealing

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Home Attic Insulation

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

Cost of attic insulation

The cost of attic insulation may vary a lot, depending on the amount of existing insulation, the size of the attic, the type of insulation, etc. But insulation costs of $300-$600 are very common.

Installing & do-it-yourself?

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

See:
Installing batts and rolls in attics
Installing loose-fill cellulose and fiberglass in attics

Insulation Materials for attics

Most attics use

1- loose-fill fiberglass, cellulose, rock wool.
2- batts/rolls of fiberglass, cellulose and rock woll.

Batt and roll insulation is slightly more expensive than loose-fill insulation.

Fiberglass is the most common and cheap insulation material, but cellulose and mineral wool are good alternatives. Cellulose, namely, is a truly 'green' insulator, with a higher thermal and acoustical performance.

See, for details:
Cellulose insulation
Fiberglass and mineral wool insulation
Reflective insulation: Radiant barriers

Recommended R-values

Attics and rooms with cathedral ceilings demand higher R-values than walls. Recommended attic insulation R-values vary with climate.

A rough rule of thumb states the following values:

- For hot climates: R-19 in ceilings below ventilated attics.
- For moderate climates: R-30 in ceilings below ventilated attics.
- For cold climates: R-39 to R-49 in ceilings below ventilated attics

For help in determining R-values in USA, use: http://www.ornl.gov/~roofs/Zip/ZipHome.html

Installing batts (and rolls) in attics

You should measure carefully the space between the floor joists, and buy batts with the proper width. A properly installation of the batts is crucial, and it involves a completely fill of joist cavities (which demand a proper width of the batts). Small open spaces will cause a high degradation in the r-value of the insulation.

Do not forget: avoid gaps and voids. Butt the ends of the batts together. In case of obstructions (plumbing stacks or other) cut the butts and fit the material around them.

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

Installing loose fill cellulose and fiberglass in attics

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

Before insulating

In old houses with attics insulated with vermiculite and perlite insulation materials (homes built before 1950), there is some chances of existence of asbestos. If this is the case, you shouldn't disturb the existing insulation, adding yourself 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.

- since insulation does not stop airflow, seal eventual attic floor air leaks.

- do not forget to seal around duct exhaust fans, cover openings, around chimney and framing (with furnace cement or high-temperature caulk) or the tops of interior walls; also air seal 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 holes.

Make sure the attic remains adequately ventilated. Insulation shouldn’t block soffit vents: they remove moisture in winter and excess heat in summer, preventing overheating…

Do not also forget to seal and insulate the vertical walls in the attic (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