Attic Thermal Insulation

The attic accounts for a large percentage of a house’s heat loss and heat gain. Attic insulation reduces heat loss in the cold months, and prevents heat build up in hotter months, making it a priority for insulation. In new construction, insulation levels for the attic are higher than all other areas. In an old home, the attic is the first place for insulation upgrades. The attic is comparatively easy to insulate since it usually presents no space constraint, making it easy to add a lot of insulation.


Critical to a healthy attic is good ventilation, with airflow circulating into and out of the attic. Circulation helps stabilize the attic temperature and remove moisture. Ideal ventilation has vent openings low on the roof and vents high on the roof to create draft. Air will flow naturally in the low openings and out the high openings. This is usually accomplished with soffit vents at the eaves and roof top vents (mushroom vents) on top of the roof. There are many other possibilities as well.

Many homes in which the insulation has been upgraded does not have appropriate ventilation either because the insulation contractor did not add vents when insulating or because insulation now covers the soffit vents, restricting the air flow. To solve this problem, baffles can be added to create an air channel past the insulation at the soffit. Air can then flow freely into the attic and then out the vents on the roof top. If additional roof top vents are needed, it is a very easy and inexpensive upgrade.

Air Leakage

The thought behind current building science recognizes that while attic ventilation is important, equally important is sealing air leaks from the rest of the house to the attic, especially in cold climates. In a typical home, recessed light fixtures, bathroom vents, plumbing stacks, chimneys and wall cavities present numerous potential air leakage paths to the attic. Air leakage from the house causes many problems including condensation, rot, mildew and in cold climates – ice dams.

Ducting that runs through the attic should be well sealed and properly insulated. There is no point heating and cooling your attic.

Do Not Disturb the Insulation

It’s best not to disturb the insulation in the attic. Some attics have vermiculite insulation. Most vermiculite insulation contains small amounts of asbestos. Disturbing the insulation can cause a cloud of asbestos, a substance it is best to avoid or to which exposure should be limited. In some cases, the vermiculite lies under a layer of a different type of insulation. Visually, it may look like you have ten inches of fiberglass when, in fact, you may actually have four inches of vermiculite and six inches of fiberglass. If you have to disturb the insulation, check what kind of insulation you have first and take appropriate precautions. A standard dust mask is not good enough for asbestos.

Upgrading Attic Insulation

If you are upgrading your attic insulation, make sure you hire a contractor who is knowledgeable about the techniques and codes for your area. Good contractors will asses the insulation type and condition, as well as air leakage from the house and ventilation.

Source: Pillar To Post Information Series