Paul Bianchina: A few tips for installing wall insulation
Insulating a wall is a great DIY project, requiring only basic tools and simple skills. But like anything else, you’ll want to take the time to do it right in order to achieve the best results.
Probably the most common wall insulation for DIY installation are fiberglass batts with a Kraft-paper facing. The batts are available in various widths and thicknesses to match the depth and the spacing of your wall studs. They’re also available precut to standard lengths to fit certain common wall heights, such as 8 feet, or in rolls for cutting to length as needed.
Working with fiberglass insulation requires some personal protection against the fibers. You'll want to have gloves, goggles or safety glasses, and a dust mask. Wear a long-sleeve shirt and long pants to guard against skin irritation, and closed-toed shoes.
All you’ll need for the installation is a utility knife for cutting the insulation and a staple gun for installing it. You’ll also need a ladder for reaching the higher spots.
Before insulating your walls, sweep or vacuum out the wall cavities as needed. Use caulk or expanding foam and seal any penetrations around pipes and wires to prevent air infiltration and bug access. If you’re concerned about rodents getting in, embed some steel wool in the caulk or foam to keep them from chewing through it.
Place a batt into a wall cavity by pressing it in between the studs until it contacts the back of the wall, then pull it forward slightly until it's flush with the interior wall face. This pushing and pulling action will help expand it to its full depth, which maximizes its R-value, or how well it resists heat.
With paper-faced insulation, there’s a paper flange running along the length of the batt’s front. You’ll want to fold that flange out, and staple through it to secure the batt in place. However, where you staple it — to the inside edge of the stud or to the stud’s face — raises an interesting and perhaps somewhat controversial question.
In my experience, I’ve always attached it to the stud’s inside surface, because I’ve been told by drywallers that they prefer to have it done that way since it doesn’t create any high spots on the face of the stud. So, that’s the method I’ve always recommended to others.
However, a reader contacted me recently and said he thought the proper procedure was to attach it to the face of the stud, because his understanding was that it offered some additional fire protection, and that there even was some fire retardant in the paper.
Hoping to get a more definitive answer to this, I contacted the three main manufacturers of fiberglass insulation: Owens Corning, Johns Manville and CertainTeed. Here is their advice:
• Owens Corning: “The flanges can be stapled to either the inside or outside of the stud; however, if they are stapled to the inside, then there is a smooth surface on the outside of the stud to install drywall over. Some drywallers prefer this smooth surface to one that has staples on it.”
• Johns Manville: “It is more common to put it on the face of the stud mostly because ease of installing, it but inside stapling is also acceptable.”
• CertainTeed: “We recommend stapling the tab to the inside. We do not (think) that it's very common to install it on the outside of the 2x4. It doesn't really make a difference … but we do recommend slightly tucking in the ends, stapling the tab on the inside.”
So, when it comes to how and where to place the stapling flange, there’s no definitive right or wrong answer, at least as far as the manufacturers are concerned. I would, however, strongly suggest you discuss things with both your local building officials and your drywaller prior to proceeding, to see if their preferences or local codes dictate a particular procedure.
One thing all three manufacturers did agree on, however, is that the insulation’s face paper does not have any type of fire-resistant treatment, and also that is must be covered.
When you come to pipes and electrical wires, don't compress the insulation around them. This seriously reduces the R-value and also can cause the insulation to bulge and create drywall problems later on. Instead, you want to pull the insulation apart — like opening the pages of a book in the center. Tuck half the insulation behind the wire and leave the other half in front of the wire.
When you get to electrical outlets, take your time to cut the insulation correctly. Again, this maximizes energy efficiency.
You'll notice that the box typically doesn't extend all the way to the back of the wall cavity, so you don't want to just cut a notch in the insulation to go around the box, since this would leave an uninsulated area behind the box. Instead, cut your notch only partly through the insulation and then separate out a pocket the size of the box, leaving a section of insulation in place behind the box. The alternative is to insulate behind the boxes first using scraps, and then notch the insulation around the box.
Insulation is best cut with the paper facing down. Place the insulation flat on a smooth, solid surface, such as the subfloor or a large scrap of plywood. Use a piece of wood to slightly compress the insulation along the cutting line, and then make several shallow cuts with a sharp utility knife.
If the insulation batt is too short to fill the cavity, you'll need to cut a filler to take up the extra space. The filler should be cut about 1/2 inch longer than needed, so you get a good friction fit when it's pressed in place. If the batt is longer than the cavity, cut it off so it fits properly. Don't double it over or squish it into place, since that compromises the R-value.
Have a home repair or remodeling question for Paul? He can be reached by email at firstname.lastname@example.org.