Unfinished Spaces

Fiberglass wall insulation is not effective on a wall that is unfinished on one side. The air contained in the insulation material will become warm and rise, causing convection that reduces the K-value to almost nothing. The first picture on this page shows such a problem candidate – a walk-in closet with an attached unfinished storage space. While the roof is insulated between the rafters, as you can see, this insulation is entirely ineffective because the soffits are open which is required for maintaining ventilation of the roof. The actual temperature in the unfinished space will be much closer to the outside temperature than the inside temperature of the home.

The same circumstances apply to crawlspaces behind finished walls in a dormered room and any other situation where a finished wall is not covered by plywood and siding on the outside, but instead backs up to open airspace. Therefore it is important that such walls be closed so that the air becomes trapped and does not easily circulate. The picture below shows one option for doing that – with foam board and aluminum foil-covered bubble wrap. It does not hurt to insulate the door as well. In this particular case the builder used a simple hollow-core hardboard door that is visible in the next picture – a no-no for this essentially exterior door application. Short of replacing the door with an insulated one, Dr. Heet stapled the insulation material directly onto the door and added a threshold that closed the air gap at the bottom. since the rubber strip at the bottom of the door did not touch the hardwood floor that was installed in this area.

 

Here you see the finished surfaces. The insulation material was attached to the studs and door jamb with a staple gun. The three layers consisted of a vinyl vapor barrier, thin foamboard, and the reflecting aluminum foil on top.