Basement insulation
	How to insulate outside the basement
	How to insulate inside the basement
	Crawl spaces
	Open foundations
	Concrete slab on the ground

Basement Insulation

How Important Is Basement Heat Loss?

Most homeowners don't think of their basement as a prime source of heat loss, yet basements can account for 20 to 35 percent of a home's total heat loss. Basements lose so much heat because of large, uninsulated surfaces above and below grade level. Contrary to popular opinion, earth is a poor insulator. There is also a lot of air leakage through basement windows and penetrations, through cracks, and at the top of the foundation wall (sill area).

Few basements have any insulation at all, and for most homeowners this means there is great potential for improvement. Insulation can often be tied in with other repair or renovation work, such as damp-proofing or finishing the basement.

Within This Page

• Types of basement construction
• Basement assessment
• Insulate inside or outside?
  • Insulating inside
  • Insulating outside

Types of Basement Construction

The most common type of basement is the full foundation basement, which is sometimes finished or considered a living space. Full foundations are made of many different materials, as described below.

Many houses have been built with a partial depth foundation that creates a crawl space under the house. Some older homes and cottages are built up on posts and piers. The space below the house is open to the outside, although this can be blocked off. Other houses are built on a slab-on-grade, with no basement or crawl space at all.

Whatever the type of construction, most basements/foundations have no insulation at all. Even if your house was built since the mid-1980s, it may have only partial-depth insulation.

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Concrete Foundations

Poured or concrete-block foundations have been built since the 1920s, usually with parging, damp-proofing and drain tiles on the exterior. However, anything more than 20 years old is likely to be in need of repair. This type of basement can be insulated from the outside or inside as long as there are no serious water or structural problems.

Older Foundations (Rubble, Brick, Stone)

Older foundations made of rubble, brick or stone are often uneven and can vary in depth and thickness. These foundations were rarely damp-proofed and have a high mortar content, which can absorb water from the soil. They usually have a history of moisture problems and should be insulated from the outside.

Other Types of Foundations

Many newer homes are built with preserved wood foundations. These foundations are made with specially treated wood studs and sheathing and are generally fully insulated. Many homes are built without a conventional basement. Examples of these include houses with crawl spaces and slab-on-grade.

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Basement Assessment

Before planning the job, assess your basement. The following are some of the problems to look for.

Water Leakage

Major water leaks (persistent leaks and flooding in the spring and when it rains) must be corrected. This could involve a procedure as simple as sloping the grade and directing downspouts away from the foundation. The solution often requires excavating, damp-proofing, adding a drainage system and insulating from the exterior.

Minor water leaks can sometimes be corrected by directing water away from the foundation and patching the foundation on the interior.

Correct problems with sump pumps or sewer backup before insulating.

Dampness

Symptoms of dampness include staining or mould growth, blistering and peeling paint, efflorescence (a whitish deposit on the surface), spalling (deterioration of the surface) or a musty smell. Minor dampness may be corrected from the interior; more serious problems should be corrected from the outside.

Condensation can also form on the foundation walls in the summer because the air is very humid and the basement is cool.

Cracks

If the basement has an "active" crack (i.e., one that gets bigger or smaller), you should seek professional help to determine if the situation requires structural repairs.

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Insulate Inside or Outside?

Insulating on the outside is usually best from a technical point of view. Despite this, it is often necessary to insulate from the inside for economical and practical reasons. Sometimes a combination of approaches is required. Examine the advantages of each approach carefully.

Insulating Inside

This may involve installing a wood-frame wall and adding batt insulation. Another option is to use rigid board insulation with prefabricated metal channels or wood framing to hold the insulation, followed by a layer of fire-resistant material (e.g., gypsum board) that is mechanically fastened to the wall. Normally, a moisture barrier is applied to the inside face of basement walls up to grade level, and an air and vapour barrier is installed on the warm side of the insulation.

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Advantages of Inside Insulation

• It can be incorporated into a plan to finish your basement.
• The work can be done at any time of the year and can be done one section at a time.
• It is often easier and cheaper to insulate the full wall and achieve high insulating values.
• Your landscaping and driveway will not be disturbed.

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Disadvantages of Inside Insulation

• Insulating from the inside should not be attempted in basements with a moisture problem. If your basement has a history of damp or dripping walls, you should insulate on the outside. If you must insulate on the inside, take corrective measures to eliminate the moisture problem before adding insulation.
• Obstructions, such as electrical panels, wiring, plumbing, stairs, partition walls and the oil tank, make the work more difficult and the insulation and air barrier less effective. If part of the basement wall is already finished, this too may prove troublesome (although wall panelling may be easy to remove and re-install).

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Insulating Outside

This involves excavating around the foundation, damp-proofing and installing rigid insulation, as illustrated above. Flashing must be attached to keep water from getting behind the insulation, and a protective covering must be installed on the exposed sections of insulation.

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Advantages of Outside Insulation

• The outside wall tends to be more continuous and easier to insulate once the soil is removed.
• You can effectively correct any moisture problems. Rubble or brick foundations and foundations with water leakage, dampness or other moisture problems must be insulated from the outside. You can repair the foundation and damp-proof and install a drainage system at the same time.
• There is no disruption in the house and no inside space is lost.
• The mass of the foundation is within the insulated portion of the house and will tend to even out temperature fluctuations.

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Disadvantages of Outside Insulation

• Some difficulties may arise in digging a trench around the house. Excavating by hand can be a tedious, back-straining job. It is much easier if you have machinery to do the work.
• Storing the dirt can be a problem.
• Excavation can be a problem in the spring or throughout the year if the property has a high water table, and cannot be done at all in winter.
• Features such as non-removable steps, paved carports, shrubbery, trees or fences can make the work difficult.

We can also show you how to insulate outside and inside the basement.

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