adding Attic Insulation

Attic insulation can provide huge energy savings. In colder climates, adding insulation to a poorly insulated attic may save 30% or more in heating costs.

Adding attic insulation Cost

Attic insulation can be simple and cheap to achieve, even in existing homes, but should be preceded by a careful preparation involving the attic ventilation, air leaks, the repairing of the roof, etc. That can turn the simple and cheap into a rather difficult and costly task.Attic vs. ceiling insulation
Insulating an attic with good access is easier than insulating ceilings without attics. In the case of cathedral ceilings, you have to install insulation batts between the roof rafters, keeping it against the underside of the deck or roof sheeting. See: Cathedral ceilings insulation

Attic insulation costs vary with the size of the roof-attic. For a 2000 sq-foot home, the cost of the insulation materials may amount to at least to $600 - $800. A professional installation of such a attic can double that cost.

Insulation Materials

Fiberglass is the most common and a cheap attic insulation material, either in batts, blankets or loose-fill (fiber insulation).

Adding attic insulation to an existing home isn't always an easy task Cellulose (in dry conditions) and rock wool are good alternatives to fiberglass, when adding attic insulation; they are 'green' insulation materials with very high thermal and acoustical efficiency.

Left: Ceiling insulation with a non-traditional insulation material (Icynene foam)

See for details:

Cellulose insulation problems
Fiberglass and rock wool insulation
Reflective insulation for roof cooling

Recommended R-values

Attics and roofs with cathedral ceilings demand higher levels of insulation than other rooms. The geographic zone also determines the insulation needs and the R-values associated to them. Something around...

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

Batt Installation

When applying insulation batts to the roof joists, 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.

Fill the joist cavities completely. Open spaces - even if small - are a cause of lower efficiency. When buying the insulation batts, take into account the space between the floor joists.

Attic insulation with Blown fiberglass and other fibers

Fiberglass, cellulose and rockwool fiber insulation is cheaper than batts, and are an excellent solution when adding insulation to existing attics.

But though fiberglass (or cellulose or mineral wool) fiber insulation isn’t difficult to install in existing attics, it typically demands a blowing machine and a correct assessment of the number of bags and also the right thickness and R-value. Hiring the services of a professional is for this reason the best option.

Note: Fiber insulation demands also a 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.

Asbestos

There is a big chance that your old attic insulation uses vermiculite and perlite, and contains asbestos. So, be aware when adding attic insulation. Only certified contractors can handle and remove asbestos and should deal with old perlite and vermiculite insulation.

Cares

Before adding insulation to your attic, consider:

- repairing roof leaks (check the attic ceiling for water signs).
- sealing air leaks in the attic floor and around ducts and cover openings, or around the chimney and framing; also air-seal 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 after its insulation. Attic insulation shouldn’t block soffit vents, since it would prevent the removing of the moisture in winter and excessive heat in summer… Rafter gabbles is a good way to avoid such blocking.

Also 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