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Ask the expert: Sealing up a drafty basement

5:57 PM, Jan 14, 2013   |    comments
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Dianne from Boothbay Asks:

I own a 200+ year old Inn, and have owned other older homes therefore, I have spent my share of fall weatherizing.

Currently I have an area in the basement with a stone foundation that is quite drafty. I would like to know the best way to keep out air leaks in the foundation from the outside. The area of one wall is not accessible from inside, last year I stacked bags of mulch along the foundation which worked well as I used the mulch around gardens that spring. I don't need more mulch, and I would like to know a less obvious and more attractive way of insulating those areas.

I use "mortite" to insulate old windows, it is very easy to apply, seals the old sashes and is hidden well in guest rooms and common areas.

I also use "blue board" painted black to close up a fireplace that does not have a damper, the fireplace screen holds it in place.

Tom Caron of Northeast Inspection Services Answers:

This might be difficult. If by "not accessible" you mean you can look in or see the wall, you may be able to have the spray foam insulation guys get their product in there. If it's totally inaccessible, the solution would be to apply insulation, and then cover it up. Again, spray foam is the best, because it insulates and also totally air seals.

The problem is that you would have to enclose it. The solution would be to build a skirt over it. This would be a frame with a sloped board on the top and siding of some kind on the vertical surface.

Now you are facing water from your roof landing on it. You would possibly need to install a gutter over the area. Does this help?

By the way, that blue board may be leaking like crazy all around its edges. When we do a blower door test, we find amazing air leaks in places like that.

A great alternative is a chimney balloon. Google that! Also remember, those old chimneys frequently had thimbles, or covered openings along their run to the roof. Also, the interior of the chimney gets really cold in winter and makes adjacent walls cold.

You might want to put a sealed cover on the top of the chimney. A good approach is to get a piece of slate that's larger than the chimney top and attach it with silicone.

This story was originally posted on November 17, 2008.

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