How to Insulate an Attic?

A question that often comes up when our technicians are inspecting attics in relationship to roof evaluation; is “how does the insulation look?…. Do we need more?…. Do we need more roof vents?”

All are very good questions. Today; homeowners should think about their roof and attic as a system, which inter-relates with other key building components.

The roof involves a water-shedding or water-proofing system. The attic beneath the roof represents an important area of the home which is in great part responsible for the comfort level and moisture resistance of the home.

First to understand is that a properly insulated attic will greatly reduce heating and cooling costs, and can dramatically reduce the amount of energy consumed to accomplish these tasks.

The second part of the equation is to have a dry attic environment free from condensation and the possibility of creating mould. A well-insulated attic in conjunction with proper air sealing methods, and proper ventilation; will also help to mitigate such perils as ice damming during freeze-thaw cycles experienced in cold winters.

One of the ways to identify whether a home requires added insulation in the attic or other areas of the home results from simple inspection and testing.

Symptoms can be cold rooms on the top floor during winter months, and conversely, rooms that are hard to cool in the summer. Ice damming can be another symptom.

When looking into the attic, observe whether insulation levels meet the top of the ceiling rafters, or if insulation levels are below the height of the ceiling rafters. This signals inadequate insulation levels by today’s code standards. As of this writing; building code standards require an R-value of 52 in ceilings. Some insulation experts suggest that R-60 is more ideal. R-value is a measure of thermal resistance that insulation has.

If your home is more than twenty years old; it is important to identify if the existing ceiling insulation is vermiculite. Such insulation has been banned as it contains asbestos fibres. It is typically a type of loose-fill insulation in appearance, as opposed to fibreglass batt insulation. If vermiculite is present, it should be abated by a professional contractor.

The other checkpoints when surveying the attic include checking for areas of heat loss. Such areas include around electrical fixture penetrations, the top plates of framed walls where they adjoin roof trusses /rafters, attic hatches, and protrusions through the roof. Examples of protrusions can be round pipes exiting through larger square openings.

To address such air leakage points; spray foam sealing, and or caulking can help to remedy such items, and should form part of a comprehensive insulation strategy. Preventing points of air leaks serve to mitigate cold exterior air from colliding with warm interior attic air, which can result in condensation.

Related Content: Attic Ventilation and Its Importance

Also to identify when conducting an inspection of the attic is the presence of a vapour barrier that is correctly sealed and is void of any breaches. Some older homes do not have a poly vapour barrier in the ceiling. In some instances it is possible to instate a vapour barrier into the attic, to be continuously installed into and over rafter spaces; however, a more efficient approach can involve the use of two-part spray foam insulation sprayed into the rafter spaces. Additional insulation can then be added. Spray foam insulation does not typically require a vapour barrier as the foam becomes monolithic.

Attics require a properly balanced ventilation system, particularly when adding insulation, and or making the attic more airtight. Shingle manufacturers require this for the enforcement of their warranties, and to create an attic environment that can breathe.

The concept behind proper insulation, air barrier, and air sealing techniques, is to retain heat below the finished ceiling. Above the insulation level in the attic; the ideal scene is that the attic temperature should be closer to the exterior temperature.

This is where proper roof ventilation comes in to play. The correct ratio for a balanced roof ventilation system is 50% intake ventilation through the soffit and 50% exhaust ventilation through the top of the attic.

Specifically, the number of roof-related vents that are required, is determined based on the area volume of the attic, and in relationship to the pitch of the roof. As an example; a lower-pitched roof such as having a 4-6/12 pitch; may require one vent per 150 cubic feet of attic space.  Ventilation manufacturers typically supply charts that provide guidance on the number of vents required, and in relationship to the capacity of a specific vent model type.

Types of attic insulation include fibreglass batts, loose fill cellulose, spray foam, and mineral wool, among others. Consulting with an experienced insulation contractor is highly suggested to determine what types of insulation may be suited for a particular application circumstance. As an example; an attic having poor working access may be best suited to using loose fill insulation blown in.

Homes having cathedral or vaulted ceilings may be better suited to using spray foam insulation. Such ceiling configurations may require specific ventilation requirements such as continuous soffit venting and the use of ridge venting, in the instance that batt insulation is used, and an air space exists in each and every rafter cavity.

When insulating an attic; it is important to insure baffles (also known as Moore vents), are installed at roof eaves areas; to insure that insulation does not block air entry from the soffits. Such vents are designed to fit between the rafter spaces and supply an unobstructed path for air to enter in at the soffit, and then draw upward into the attic.

Certainly, a new build home or a complete renovation home represents the best opportunity to achieve maximum insulation value.

For retro-fit homes; enlisting the services of a licensed energy auditor can be a worthwhile activity which will pay dividends in terms of final energy savings, and initially; in terms of identifying areas throughout the home (not just the attic); where measures can be taken to limit air leakage, and improve insulation levels and occupant comfort.

As the Canadian Government offers grants for insulation upgrades; having a proper audit conducted, allows the homeowner to demonstrate the existing scene versus the improved scene, once retro-fit work has been completed.

As the subject of insulating attics and homes is an extensive subject; and as each home may have very particular circumstances, using a professional and credentialed insulation contractor, is a home or building owner’s best pathway to a properly assessed and completed project.

To learn more about roofing, insulation and related services; visit