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Insulation for Bay Windows

Q. My house is 7 years old. There is a 5-window bay in the master bedroom and a picture window bay in the master bath. These rooms are always colder than the rest of the house. My questions is - could it be the insulation? The builder had put a layer of the pink batting between the rafters (under the bay windows from the basement) the full length of the bay (from basement to outer wall of the bay). When the superintendent saw it he said it shouldn't be laid out that way and placed a smaller piece at the end of the opening just like the rest of the basement. In other words, there is no insulation that would be under the floor part of the bay. Could this be the problem? The floor in the bedroom is carpeted but the bathroom is tile and the closer you get to the bay area the floor is very cold. Do you have any other suggestions?

A. This is a very common problem with bays and bow windows. The area is simply under heated. The superintendent is right to keep the insulation on the perimeter of the joists. AND the floor part of the overhang under the window needs insulation too. He moved the insulation to allow heat from the basement to get to the underside of the bay floor from the basement. BUT the cold floor is simply because there isn't enough heat source in the bay to match the heat loss in a bay window protrusion that is exposed to the elements on all five sides, top, bottom, left, center, & right sides. I suggest a space heater or another heat register be added to the ductwork to increase the flow that bow area.

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