Architectural Designs

has anyone used mylar in attic now being insulated to reflect heat back?

I am rehabbing a wood bungalow house that has one gable roof side getting sun all day long. I plan to tape mylar over the insulation between the joists under the drywall to reflect heat radiation back to the outside. Has anyone ever tried this?

Public Comments

1. I used foil-faced rigid insulation, 4x8 sheets.. Reflects heat away from the cooled space and keeps heat in during the winter. I used it in conjunction with regular, high-density fiberglass batts. I have VERY low utility bills. Average about $165 per month - total electric - in a 4,900 square foot home.
2. The technique you are talking about---using a reflective surface to block radiant heat transfer---is called a "radiant barrier". I have installed one in my attic on the underside of the roofing with the shiny side facing down into my attic. It works well. The trick is to let the shiny surface face an open airspace without touching anything. Even if the mylar or foil itself gets hot from contact with the roofing or outer wall, it won't re-radiate that heat into the interior space. If you are going to install it inside a wall, you need to leave a space between the shiny surface and the wallboard. Allowing the metallic surface to touch the inside of the wall will simply allow conductive heat transfer and defeat the radiant transfer barrier provided by the shiny/reflectve surface. For more information, check out the Florida Solar Energy Center Radiant Barrier design notes hosted at the University of Central Florida in the reference.