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Bathroom Insulation

Bathrooms are among the most frequently used rooms in the house. So not surprisingly, controlling moisture is a major concern when it comes to installing insulation in bathrooms. That's because all of the everyday activity such as showering, bathing and washing adds moisture vapor to the air. This moisture vapor is transferred along with heat. This is especially common in humid environments. When moisture vapor becomes trapped in walls, mold and mildew growth can result, damaging your home and presenting a potential health concern to you and your family.

You can avoid these problems by installing insulation that offers excellent moisture control properties. To minimize the possibility of vapor collecting under the insulation, a vapor retarder is generally installed (according to local codes). Johns Manville's MR® Faced Batts are recommended in regions of the country where vapor retarders are required. Consult your local building code for possible vapor retarder requirements. You can also learn more about the proper use of vapor retarders on this website. To do so, click here.

Proper bathroom insulation also will help keep the room a comfortable temperature year-round.


How to Install Insulation in Interior Walls

  1. To install in interior walls for good sound control, apply caulk between the top plates and at the bottom plate and floor. You should apply sealants or caulks only to clean, dry, oil-free surfaces. Smooth caulking with your fingertip or a putty knife.
  2. If you are using faced batts, place the batts into the wall cavity and staple the flanges of the batts to the inside or the face of the studs about every 12". 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.
  3. 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.
  4. Fill in any narrow gaps between joists by forcing pieces of unfaced insulation into the gaps with a screwdriver or putty knife.

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.

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.

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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