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Air sealing and insulation question

I am buying a 1900 bungalow in the white mountains of NH, 10 foot ceilings 4 inch walls. The only insulation now is the attic is capped. The heating is hot air, with unsealed or insulated duct work. The house is one story. We are closing in October, so I'll have no access until then. Where should I start?

Asked by Ken Chester
Posted Tue, 08/12/2014 - 14:16
Edited Tue, 08/12/2014 - 15:16

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7 Answers

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The ducts are in the basement, and not in the attic above the insulation, I hope(?).

Is the basement sealed & insulated?

Any fireplaces?

Fixing the leaks at the attic-floor plane and at the basement o subdue the "stack effect" are far more important than leaks in between. Flues and plumbing/electrical chases that run from basement to attic are often huge thermal by pass stacks for moving air. Foundation sills & band joists are typically several times leaker than all of the window & door leakage combined.

If you can't see any big leaks, it's probably worth doing an air sealing pass with a blower-door & infra-red imaging to map out big leaks though wall-framing etc to seal those up best you can prior to adding wall insulation.

The wall construction type/ stackup may dictate how the walls get insulated.

Answered by Dana Dorsett
Posted Tue, 08/12/2014 - 18:22

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We have to know more details. Is this a year round home, summer home, winter skiing? How far are you willing to go to insulate the home? Tear out the walls, new siding, new roof? Is the duct work located in the insulated part of the house or outside of it.

So first tell us what you hope to do with the house, then you can get much better advice.

As you know, the first priority is air sealing before insulation.

The White Mountains are beautiful. It would be lovely to have a house there.

Answered by Lucy Foxworth
Posted Tue, 08/12/2014 - 18:23

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Dana and Lucy, Let me give more details. I live in southwest NH now, but my neighbor wants to buy my property, long story. This new house will be a year round house starting next June. This new area of NH, gets very cold -30 to -40, so air sealing and insulation will be important. All the ducts are in the basement. The construction type is balloon frame and from what I can tell 4 inch walls. The interior has plaster walls, the exterior is clapboard siding. The heat is oil via a Thermopride furnace. My old house had one of the same furnaces, but I heated with two Woodstock wood stoves and that's the goal here as well. Lucy asked how far I am willing to go. The house I am selling now has 2” of foil face urethane in the floors and 4” in the walls. I had 4” of spray foam put in the gable ends and the roof bays. We did a cold roof giving ventilation the entire way from soffit to ridge vent. This house has four peaks and would be a challenge to do that this time. The attic is a full walk-up, but I plan to keep it as an attic. There is one fireplace plus one other chimney, that serves the furnace. The basement is not sealed or insulated. The basement is stone with a granite foundation, it's a full basement. I am very familiar with air sealing thanks to this site and Building Science. I am always looking for a way to make an old house energy efficient. Thank-you for your help and advice.

Answered by Ken Chester
Posted Tue, 08/12/2014 - 19:31
Edited Tue, 08/12/2014 - 20:31.

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There is no place in NH with 99% outside design temps anywhere near -30F (but if this is at 3000' of altitude that will be more than a once per decade event.)

If the house has an uninsulated quarried granite basement it's worth putting up 1-2" of closed cell foam and a rock wool or unfaced fiberglass insulated studwall (with no vapor barriers-kraft facers would be OK.)

The fireplace is a 24/365 air leak- even worse if it happens to be on an exterior wall. If you're planning to install a woodstove or wood burning insert in the fireplace firebox, it's worth doing some masonry work and installing a sheet-steel air-barrier where the new flue liner will drop through the masonry smoke-chamber to tighten it up a bit. While it's impossible to get a perfect air seal between the liner and the steel air-barrier, you can do pretty well with automotive exhaust sealants.

Answered by Dana Dorsett
Posted Thu, 08/14/2014 - 16:08

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Hi Dana, There are nights when it does get to -30F, but it seems like a nights few per season. The average low in Jan and Feb are 2-3 degrees F still much colder than where I live presently. Would you use closed cell spray foam on the basement walls or somehow use 2" urethane sheets? The stud wall would you use pressure treated lumber? Are there some links here on GBA you could point me towards for further study? Thanks for your guidance. Ken

Answered by Ken Chester
Posted Thu, 08/14/2014 - 20:34

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With granite or fieldstone foundations it's harder to make permanent attachments with good air seals using rigid foam, whereas spray foam becomes a monolithic self-attaching monocoque. Even if it seperates from the stone and shifts a bit over time, it will remain air-tight. (With poured concrete or CMU foundations sheet-goods can work pretty well though.)

Is there any sort of basement slab or ground vapor retarder?

Answered by Dana Dorsett
Posted Fri, 08/15/2014 - 10:13

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The basement does have a slab. but I doubt there is a vapor barrier in place. Would using 3 or 4 Rinnai wall furnaces in place of the ducted hot air furnace make sense? Therefor I could insulate the floor with ridge foam which would air seal the basement. We plan to add a gas range for cooking and for heating the hot water, so propane will be on site. We did it here in the current house and it works great. We heat with 3 cords of wood and use the Rinnais as backup only. I'm thinking of the cost of spray foaming an 8 foot wall on a 49x33 basement.

Answered by Ken Chester
Posted Fri, 08/15/2014 - 10:27

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