‘Tis the season to bank on basement insulation

Posted Nov. 13, 2009, at 5:27 p.m.

Banking the house was a common practice for many years in Maine. It was a way to protect the old rock mortar foundations from wind and cold. Most older homes tended to have major holes that allowed cold air to blow in, and being masonry they tended to get pretty cold. Banking or laying evergreen boughs or wooden boards against the foundation did a fairly decent job of keeping the basement warm.

These days, not many people build their foundations with stacked rocks that are mortared together. Most basements are poured-in-place concrete that are made with removable forms. The beauty of the modern basement is that the walls are quite strong and they usually do not have holes in them.

Most savvy builders install foam insulation either inside or outside of the foundation wall. Of course, the placement of the insulation is a point of contention.

The outside foam insulation people will argue that insulation on the exterior will protect the foundation from freeze damage and also will offer some level of moisture resistance. The downside is that if the foam insulation goes up to the wooden part of the house, it can create a pathway for bugs to get into the house undetected. Carpenter ants and termites (yes, there are some termites in Maine) can find their way to the wooden parts of the house.

And the foam can get damaged by lawnmowers and UV solar degradation if not protected.

So, the interior foam insulation people laugh and say install the foam on the inside. For years we were concerned that insulating a basement wall on the inside would allow freezing temperatures to cause damage to the walls. And for many years, we would not insulate the bottom foot or two of the basement wall in order to allow some heat loss to help protect the wall from frost cracking. This concern does not seem to be an issue with a properly constructed modern concrete wall.

For about the past 10 years some people feel the next big foundation concept has been something known as the insulated concrete form, or ICF. This is like a big foam Lego block that is stacked and filled with concrete. What great fun! Why should just kids get to play with stacking blocks?

I am not enamored with ICFs given the cost and fact that they can be susceptible to degradation from the sun, bugs and wear and tear. The cost also seems high compared to a more conventional foundation with a proper insulation system.

So what to do? I like the idea of insulating on the exterior from the footings up to grade level. Then I would leave the bare concrete for the above-grade foundation.

The problem is that this is the biggest heat loss area of any foundation, so we should then insulate it on the inside from the sills to a couple feet below grade. In this way, we have covered all the bases and preserved the foundation’s integrity without sacrificing durability — and saved energy.

Anytime anyone suggests a scheme for insulating, there is always someone who will suggest an alternative concept. A given area might warrant a different insulating practice.

If I was doing over an old house with a rock mortar wall, I would have it sprayed inside with foam from the sill to the floor. Spray foam does an outstanding job of insulating and sealing the rough irregular surfaces of an old wall. It is not cheap, but it is worth the investment.

I used to not like basements given the cost and difficulty in keeping them dry. There is enough technology around now to allow us to build dry, warm basements at a reasonable cost.

Questions for Tom Gocze should be mailed to The Home Page, Bangor Daily News, P.O. Box 1329, Bangor 04402-1329. A library of reference material and a home-project blog are at www.bangordailynews.com/thehomepage.html.

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