How To Install Wall Insulation
How to Install Insulation on an Unfinished Wall
Insulating a wall is similar to assembling a giant jig saw puzzle where you have to cut each piece to fit. Treat each section of the wall as your next puzzle piece. Measure the space and take note of any wires, pipes, electrical outlets or light switches along the way. Cut each piece to fit and tuck it into place. Take special care to cut around the wires, pipes and electrical outlets by cutting notches or filleting the insulation so it goes around the obstructions.
Cutting Insulation for a Wall Cavity
You can cut the insulation with a standard utility knife but I spent the extra 10 bucks for a long blade snap knife. It has a longer blade that makes it easier to get a nice clean cut. And when the tip of the blade gets a little dull you just snap off the end.
If you've never cut insulation before, all you need to do is:
- Roll it out on the ground.
- Hook a measuring tape to the end of the roll and pull a measurement.
- Put a scrap piece of plywood under the spot you plan to cut.
- Compress the insulation where you need to cut with a board, a square or a level.
- Run your knife along the board to make a nice clean cut.
Note: I always cut the insulation 1/2" longer than the wall cavity to make sure it fits snug at the top and bottom.
Installing Insulation in Narrow Wall Cavities
When you run into wall cavities that are not the standard width, you'll need to cut a long thin piece. Grab a level or long straight board and lay it on top of the insulation. Hook your tape measure to the edge of the level and look straight down on the insulation. Make any adjustments to the level to line up your cut and make sure you have plywood underneath it. Then make your cut and move down the insulation lining up the level and cutting until you reach the end.
Buying the Right Insulation for Your Walls
Most walls are framed with 2X4s 16" on center. Which leaves a 14 1/2" gap that's 3 1/2" deep in between the studs. Perfect for the cheapest and most common 15" wide R13 fiberglass insulation. Walls vary in height which usually means buying rolls of insulation and cutting them to fit. But if your walls are exactly 92 5/8" high, buy the pre-cut batts and save a little time. If the walls are framed 24" on center or have 2X6 framing buy insulation that fills the space like 5 1/2" deep R19 or insulation that's 23" wide.
If fire prevention is your main goal, consider buying rock wool insulation for the walls adjacent to your living spaces. Rock wool is a dense, fire proof insulation made from volcanic rock. Installing rock wool insulation is the same as installing fiberglass insulation. You can buy Roxul rock wool insulation at The Home Depot.