Ask the Renovator: The Best Insulation to Seal in Air and Stop Moisture


Q In a previous article, you discussed the use of Icynene and open and closed cell insulation (“Ask the renovator: a house with a mansard roof needs insulation. But what kind?” , May 29). We got two quotes for air or water proofing from Mass Save and a professional spray insulation installer for the top of our basement foundation. The professional spray insulation installer recommended the open cell because of its waterproofing and airtight properties. However, he said we would need to be out of the house for 24-48 hours due to the gas he releases as he hardens. Mass Save recommended closed-cell air sealing, but made no mention of leaving the house while drying. The open cell cost twice as much as the closed cell.

The facility is in a heated, finished basement that has had three burst pipes in recent years during typical February snap freezes below 20 degrees. They happened even though we keep the heat at 55 degrees. I was told to wrap the hot water pipes around the foundation wall, install uncoated insulation batts around the pipes that lead outside and turn the heat up to 65 degrees in winter.

What should we do, and more importantly, what would you suggest that would not require us to leave the house for a day or two? Restriction is a deciding factor. My wife and I are concerned about poison gas and leaving our house during this time.


A. While you can use open cells around the top of the foundation wall, it’s certainly not the best for stopping moisture or air sealing. The closed cell is far superior for both categories. (I don’t know if it was a typo, but the closed cell should cost twice as much as the open cell. Not the other way around.)

As for what time you need to be away from home, this is something you should discuss with your installer. There is a big difference in the formulas used for the installation of Icynene. The formula used by our installer allows for a one hour re-entry with adequate ventilation, which means opening windows and fans when possible. To help you in your planning, ask your installer for the Material Safety Data Sheet (MSDS). All installers have access to it.

A key to preventing these pipes from freezing is to use the closed cell (which has a higher R-value) and make sure it goes around the back of the pipes, closest to the outside. You actually want to keep them exposed to indoor temperatures as much as possible while sealing them from behind.

Mark Philben is Project Development Manager at Charlie Allen Renovations in Cambridge. Send your questions to [email protected]. Questions are subject to change. Subscribe to The Globe’s free property newsletter – our weekly digest on buying, selling and designing – at Follow us on Twitter @globehomes.

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