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Wall Insulation - Exterior

An exterior wall is any wall that faces outside or otherwise separates conditioned spaces from unconditioned spaces, such as knee walls and basement walls. These walls should be thoroughly insulated in order to create the all-important thermal envelope around your living space. Properly insulated exterior walls make all the difference between a comfortable, energy-efficient home and a drafty one.

Take time to fit the insulation carefully so heat cannot escape in the winter and the inside stays cool in the summer. A good, tight insulation job saves energy, saves money, and protects your home for the future.

Since exterior walls typically have a lot of plumbing and wiring running through them, review the Special Considerations for tips on installing insulation around these obstacles.

JM insulation is manufactured in standard widths designed to fit the most common wall cavities. However, occasionally you may encounter nonstandard-width cavities. In these situations, you will probably find our EasyFit® Batts to be the best solution.

EasyFit® insulation features vertical perforations that allow you to easily tear the insulation by hand. The perforation pattern accommodates most non-standard-width cavities. Or if you use JM ComfortTherm®, Kraft-faced or Unfaced batts, you can cut them by hand with a utility knife using a 2x4 as a straight edge.


How to Install Insulation in Exterior Walls

Insulation should be installed in all exterior walls that separate conditioned spaces from unconditioned spaces, including knee walls and basement walls.

  1. If you are using faced batts, place the batts into the wall cavity and staple the flanges of the batts to the inside or face of the studs about every 12 inches. Kraft facing must not be left exposed. It must be covered with gypsum board or another approved interior finish. Where an exposed application is required, use FSK-25 flame-resistant faced insulation. If you are using unfaced batts, place the insulation into the cavity, making sure that it is the correct size and fits snugly at the sides and ends and does not protrude in the back.
  2. If the insulation is too long, cut it to fit properly. Don't double it over or compress it. Use a sharp utility knife and straightedge. Cut batts on a smooth, flat surface, and cut them about 1" larger than the framing cavity. If the material is too short, cut a piece to size to fill the gap.
  3. Fill in any narrow gaps between joists by forcing pieces of unfaced insulation into the gaps with a screwdriver or putty knife.
  4. To control air leakage, apply caulk or foam sealants around openings like window and door frames and any openings where wires or pipes go through the exterior wall.

To apply a vapor retarder:

  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 inches.
  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

JM Spider® Custom Insulation System


JM Spider® custom insulation sprays-in filling all gaps and voids in your walls, significantly improving energy efficiency, sound control and family comfort.

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.

EasyFit® Batt Insulation


JM's EasyFit® Formaldehyde-free™ insulation is available unfaced or with kraft facing, and has vertical perforations for fitting non-standard wall cavities.

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.

Unfaced Batts and Rolls


JM's Unfaced Insulation is a lightweight thermal and acoustical fiber glass insulation made of long, resilient glass fibers bonded with an acrylic thermosetting resin made without formaldehyde.

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