Insulation no image

Published on June 5th, 2013 | by Henri

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Insulating underneath a bay window

Q.    My house is about four years old, and I am still finding things that are wrong. (Too bad the New Jersey New Home Warranty Program is really only good for the first year — unless there is a major structural problem.) Anyway, I have discovered cold air coming in where the wall meets the floor in the area of my living room that juts out because of the bay window.

I was able to access the bottom of the bay from my basement. There is only a small amount of insulation that is vertical — it goes from the foundation to the floor joists above. I was able to remove it and see that there was no insulation under the floor of the bay itself. In other words, there is a vinyl soffit cover, then the plywood floor. No insulation at all. All that cold just runs right into the house. Shouldn’t there be some type of insulation there? What type should I use? I can shove it in from my basement.

A.    The simplest thing to do at this point is to measure the depth of the floor joists and buy fiberglass insulation that will fill the entire depth. For instance, if the joists are 2-inch by 8-inch (actually 7 -1/2 inches deep) or 2-inch by 10-inch (actually 9-1/4 inches), buy R-30 batts with an integral paper or aluminum vapor retarder. Although they are labeled for 9-1/2-inch spaces, squeezing them to fit between 2-inch by 8-inch joists will not materially affect their performance one way or the other. Wear gloves and a mask, and carefully work the batts in with the vapor retarder up. Make sure there are no voids anywhere.

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