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Installing Vapor Retarders

Moisture in the air in the form of vapor is transferred along with heat. This is especially common in humid environments and in certain areas inside a home - such as bathrooms, kitchens and laundries. When moisture vapor becomes trapped, mold and mildew growth can result. These can damage the home and present a potential health concern to the home's residents. Vapor retarders keep the moisture in the air in your house from condensing in the insulated cavities.

Insulation facing usually acts as a vapor retarder. If you need a vapor retarder and your insulation is unfaced, you must cover it with a polyethylene film.

JM's Kraft-faced, ComfortTherm®, and MR® Faced insulation provides a vapor retarder (The MR® facing is treated to resist the growth of mold and mildew).

Whether your vapor retarder is a facing or a film, it is usually placed on the warm side of the wall. If you live in a cold climate, place the vapor retarder between the interior of your home and the insulation. If you live in a hot, humid climate, place the vapor retarder toward the outside of the wall cavity.

How to apply a Vapor Retarder

Installation Tips

  1. To apply the poly film, start at the top plate in one corner of the room.
  2. Pull the film tight and staple at least every 12".
  3. Drive staples at the center of every stud and around openings, working around the room.
  4. Overlap the sheets by one complete cavity to minimize leakage. Then staple evenly through, fastening both sheets to the studs at one- to two-foot intervals.
  5. Pull the film tight along the sole plate and staple in the same manner, making sure the staples are driven flat, flush to the stud surface.
  6. Trim out the poly from over windows, doors and electrical boxes. NOTE: In areas of the country where vapor retarders are not required, bathrooms would require unfaced insulation and no poly film covering to allow moisture to escape.

Related Products

ComfortTherm® Batts and Rolls


ComfortTherm® insulation is a lightweight, thermal and acoustical insulation made of long, resilient glass fibers bonded with an acrylic thermosetting Formaldehyde-free™ binder.

MR® Faced Batts


MR® Faced Batts are a lightweight thermal and acoustical fiber glass insulation made of long, resilient glass fibers bonded with an acrylic thermosetting Formaldehyde-free™ binder.

Kraft-Faced Batts and Rolls


JM's Kraft-Faced Batts & Rolls are made of naturally white, Formaldehyde-free™ fiber glass, reducing environmental concerns including the risks of poor indoor air quality and the effects of manufacturing on the environment.

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