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In the closet of an upstairs bedroom, there is a door about 3/4 the size of a normal door that leads to an unheated attic space. It gets pretty chilly in that closet during the winter months, since the door is a simple hollow core wooden door that does very little to keep out the cold air in the attic.

I'd like to add some insulation to the attic-facing side of the door, but I wasn't sure if I needed a special insulated foam board or some other kind of insulation for the task. Would a general purpose foam board adhered to the door be the best way to keep the closet warm?

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Rigid foam insulation will be the easiest to install, since you can simply screw it on. The blue or pink stuff should be fine, and they are easier to handle than Poly-Iso (yellow with a foil backing). You should pick up a pack of insulation washers, often sold for duct insulation, at your home center or on amazon. These are essentially large domed plastic washers, which flatten against the foam board, and provide a much stronger connection than a simple screw-head. Make sure you place your screws into the solid wood at the edges of the door too, so they don't pull out of the flimsy center.

You should really look at air infiltration first though. Make sure you run weatherstripping (either rubber gasket or foam strip) all around the opening. Make sure it latches snugly.

Even a heavily insulated door won't do much good if you have a 1/4-inch gap running around the frame.

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  • Thanks, I did add some extra weather stripping around part of the door where it didn't close completely against the rubber gasket that was installed. If I do go ahead with rigid foam board for the back of the door, would faced or unfaced insulation be best? My attic is pretty well insulated but of course not heated. I'm not sure if I need to worry about condensation building up within the insulation in this scenario.
    – Derek
    Commented Jan 15, 2016 at 16:19
  • XPS (blue/pink foam) is already a vapor retarder. I would generally avoid adding a vapor barrier to it, unless you are already having trouble with condensation, and faced xps is pretty rare. This is a small part of your housing envelope, and vapor barriers can cause more trouble than they prevent if done wrong.
    – ench
    Commented Jan 15, 2016 at 16:35

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