Rigid foam insulation helps increase energy efficiency in your home. Inch for inch, rigid foam offers a higher R-value than either fiberglass batts or wood cellulose products, meaning it insulates more. Even better, rigid foam insulation, unlike other products, resists moisture and condensation. But rigid foam insulation ignites easily, so building codes insists that the insulation is covered by drywall, which is fire resistant. While you could install furring strips to anchor the drywall to, using the proper adhesive and a long drywall screws to penetrate the studs behind the insulation is sufficient, quick and simple.
Things You'll Need
- House-wrap tape
- Expanding foam
- Construction adhesive rated for use with rigid foam
- Caulk gun
- Drill or screw gun
- Drywall screws
- Utility knife
- Tape measure
- Drywall tape
- Joint compound
- Drywall knife
Check each seam in the rigid foam insulation. Cover each break in the insulation with house-wrap tape to maintain the insulation's vapor- and moisture-barrier qualities.
Squirt expanding spray foam in any gaps along the edges of the wall or ceiling, especially near the ceiling joist or other voids. Trim as necessary with a utility knife to leave a flat surface. This completes the moisture and vapor barriers, since foam is impervious to transmission of any kind.
Mark an adjacent surface to indicate where the framing members such as studs or joists run. If you are covering walls, mark the floor or ceiling. For ceilings, mark the walls instead. Typically the insulation seams indicate the presence of wood studs or ceiling joists. With masonry walls, you can drill into any spot you wish.
Load a caulk gun with a tube of construction adhesive that states it is safe for foam insulation. Squirt a generous bead of adhesive over an 8-by-4-foot section of the rigid foam insulation in the top or far corner of the area you are drywalling. Avoid any adhesive not formulated for use with foam; these products can melt or degrade the foam, ruining your insulation.
Lift the drywall sheet and push it into place snugly against the wall or ceiling edge. Drive long drywall screws through the surface, past the rigid foam insulation and into the framing elements underneath. Since you are using adhesive, a screw every 16 to 24 inches both across the sheet and down the sheet is sufficient. Drill holes and insert masonry screws alternatively. Sink screws slightly beneath the surface.
Work across the surface, continuing to glue and screw sheets of drywall. Butt each new sheet of drywall against the preceding sheets. Stagger the joints, cutting a sheet of drywall if necessary, to avoid unbroken seams across the length or height of the wall.
Cut drywall as needed to allow for windows, doors, light switches, electrical outlets or other objects. Spread chalk along the edges of small items you plan to cut out of an unbroken sheet, then hold the drywall in place to create an outline of the object on the back of the drywall.
Align a straight edge with the edges of the cutout, or measure and mark the drywall to show where to cut the entire sheet width- or lengthwise. Score the drywall with a utility knife. Punch out the cutout or bend the cut section up abruptly to snap the remainder loose.
Spread a thin, even coat of drywall compound over each seam in the drywall and over every screw head. Coat each corner or drywall edge as well. Cover each seam with a piece or strip of drywall tape, running a drywall knife across the tape as you apply it to force air out from underneath.
Layer another coat of compound over the first once the surface dries. Feather it into the surrounding drywall, making the layer thinner the farther from the tape it spreads. This prevents ridges from a thick buildup in one spot only. Allow the compound to dry again before proceeding.
Sand the seams and screw locations smooth, running your hand over to feel when the area is flush with the surrounding area. Repeat, applying another layer of compound, drying and sanding as needed until the joints and heads beneath are hidden and the wall feels completely smooth.
Prime the drywall and top with one or two layers of paint. Trim the wall or ceiling as preferred and replace any outlets or fixtures removed to complete the installation.
Tips & Warnings
- Running the drywall sheets horizontally is preferable as it creates seams beneath eye level, near your waist or chest. Position the sheets vertically if desired instead. Gluing and screwing the drywall remains the same in either installation.
- In most cases, using adhesive alone is insufficient to install the drywall over rigid insulation. Especially when using thicker, heavier drywall, the weight can tear the drywall loose from the foam underneath. Using adhesive is thus a way to make installation easier, relieving some of the drywall weight you must support while attaching and allowing for fewer attachments.
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