Komorowski’s Korner – Insulating The Basement by Richard Komorowski – Cornwall Ontario – May 4, 2010

Insulating the Basement

Cornwall ON – The average basement typically accounts for a major heat loss unless it is properly insulated. The good news is that a poured concrete basement (as opposed to concrete block or field stone) can be easily and effectively insulated by the homeowner.

The first and most important step is to make sure the basement is dry. If you try to insulate a wet basement, the result will be mould and a toxic living environment. Don’t forget, too, that fibreglass and cellulose insulation only work when they are dry.

If the basement is prone to leaks, you must fix these leaks first. Several factors contribute to a leaky basement:

  • Cracks in the foundation or basement wall itself. These may be minor, and could possibly be patched with hydraulic cement, or they could be structural, which means that one day your whole house might suddenly come down. If you’re not sure, contact a qualified, licensed contractor.
  • Outside ground that slopes towards the basement wall will carry rainwater towards the basement, not away from it. If this is the case, consider doing some landscaping.
  • Is there an adequate eaves trough, and if so, is it functional? Without an eaves trough, the rain from the whole roof concentrates a few inches away from the basement wall, which quickly saturates the soil.
  • Does the downspout drain to a suitable point, downgrade and several feet from the wall? If not, the ground in this area saturates very quickly and the water might force its way into the basement.

If the leakage is relatively minor, it can often be controlled by attention to the above points, and possibly by installing a sump pump, with appropriate drainage channels, within the basement itself.

If none of these steps work, then it will necessary to have a contractor with a back hoe dig around the entire basement, repair or install tile drainage around the foundation footing, and then seal the entire wall with tar. This is expensive, especially the labour cost, but you can add a lot of usable living space to your house. As a bonus, with the outside all dug up, you can very easily insulate the basement from the outside, using rigid foam panels.

There is some controversy about how to insulate a concrete block or fieldstone foundation. Some authorities maintain that these basements can be insulated from the inside without problem, whereas other experts think that this will eventually cause structural failure.

The reason is that if the basement in not insulated, it warms up the soil around the wall, preventing it from freezing. Because it is not freezing, the soil around the walls remains stable, and the walls do not go through a continual freeze/thaw cycle that eventually crack the mortar (which will then cause the basement to leak).

When wet soil freezes, it tends to heave up. If the soil also freezes to a block or field stone wall, it will want to try and lift the wall with it, causing potentially severe damage. However, if the wall is insulated on the outside, the wall’s temperature remains above freezing throughout the winter, and heaving soil has no effect because it is not in direct contact with the wall. Poured concrete walls, being relatively smooth, do not suffer from this effect.

Insulating from the inside is quite simple – build a stud wall (preferable 24” on centre) and insulate with either fibreglass batting (R12 or R20, depending on whether you use 2 x 4 or 2 x 6 studs), cover with a proper vapour barrier (very important), and then finish with dry wall or panelling. As an alternative, you can also use rigid foam boards, which often have a higher R value per inch of thickness. However, if you use any kind of foam insulation, it is mandatory to cover it with some sort of rigid material. Dry wall is the safest and, in my opinion, the most aesthetically pleasing, but the Ontario Building Code will allow other materials. The reason for covering foam is for fire safety. If a fire starts and comes in quick contact with the foam, toxic fumes can kill you and your family before the smoke alarm can go off.

The current Ontario Building Code recommends insulating from the top of the basement to the floor. If this is going to be a potential problem because of dampness, it’s fine to leave the bottom 12 to 18 inches clear, without insulation.

While in the basement, also check that the smoke alarm and CO (carbon monoxide) alarms work. A few seconds holding your ears and testing them might save your family’s lives, as well as lessening the property damage.

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