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Sheep Dog Hollow: an eco-friendly renovation

Is spray foam insulation the best choice for an old house?

In renovating an old house, is spray foam insulation the way to go? And which type of spray foam insulation - open cell or closed cell?

By / December 2, 2009

The slats in the walls of the farmhouse suggest how drafty this building must have been during cold New England winters.Salvaged doors and wood are being saved for the new construction. Now the renovation decision is: What type of insulation to choose?

Joanne Ciccarello/Staff/The Christian Science Monitor

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Want to get confused? Listen to several contractors tell you the best way to insulate your drafty old house.

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Alexandra writes about the "green" and budget-friendly renovation of a 100-year-old farmhouse in south-central Connecticut.

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That’s exactly what I did last week. And after puzzling over how people could come to such widely varying conclusions, I have now emerged from the experience better versed on spray foam technology than I ever thought possible – and am almost, but not quite, ready to make a decision.

Early on I opted against traditional fiberglass batting (pink or yellow) because, from my earliest research, I thought that it was clearly not the best choice for us, even though it’s the least expensive in the short term.

The primary reason has to do with our decision to put in geothermal heating. For it to work optimally, a house has to be as airtight and insulated as possible. With a 1902 farmhouse with plenty of nooks, crannies and cracks, fiberglass batting just won’t do the trick, according to the various experts I spoke with.

So we knew we wanted to put in spray foam insulation – and a good, green spray foam at that.

“Spray foam gives you an air barrier which is our secret weapon – it doesn’t allow for any air movement like fibrous insulations,” says Ned Williams of Connecticut Spray Foam Industries in East Haven, Conn. “Air infiltration is really becoming enemy No. 1 in the insulation battle, while R-value is turning out not to be the simple savior.”

OK, once we decided to use foam to seal up our leaky house, the next question was whether to choose open-cell or closed-cell foam?

Open cell is flexible, made up of what are essentially billions of minuscule broken bubbles. It’s water permeable and less expensive than closed cell. But it doesn’t produce as high an R-Value.

Closed cell is more solid, like a foam board. That makes it a bit brittle, but also gives it a higher R-value.

The contractors from both Anchor Insulation and Connecticut Spray Foam Industries recommended open-cell insulation for most of the house – in part because the closed-cell foams create a vapor barrier and are impermeable to water.

“If you have a leak in the roof – and eventually they all leak – where is the water going to go?” says Mr. Williams. “If it’s a two-pound, closed-cell vapor barrier kind of foam, the leak’s going to stop at the foam and that water will be trapped in the system. If it’s an open cell half pound system that water’s going to drip right through.”

Ever hear of mold? Preventing it sounds like a good reason to us to go for the open-cell foam.

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