15 May Adding Attic Insulation

Homeowners often overlook one of the easiest and most cost-effective ways they can cut down on energy bills: adding attic insulation.

Tankless water heaters and solar systems may be sexier upgrades, but most attics are woefully under-insulated (especially in older homes). Adding insulation to an attic can immediately lower home heating and cooling bills and is a relatively inexpensive upgrade that can pay for itself in as little as 6-9 months. While looking to cut down on the energy bills don’t overlook windows either.

Blown attic insulation

Blown attic insulation is an increasingly popular choice when it comes to adding attic insulation, as it frees you from the laborious chore of cutting and install fiberglass batt insulation. Blown in attic insulation is more costly per square foot and has a slightly lower R factor as compared to batts, but it’s much quicker and easier to install correctly.

Attic insulation needs to provide a seamless barrier that prevents air flow from your home below to your attic. This is much easier to achieve with blown insulation, as the method of applying it ensures a seamless blanket of insulation. Its more difficult to achieve the same goal with batts, as you must be careful and precise when cutting batts and working around ceiling joists.

Homeowners and DIYers can blow in attic insulation themselves, as most home improvement centers rent the machine (or essentially rent it for free if the insulation is purchased there) and it’s relatively easy to use. If you decide to go with the professionals for this job, expect to pay from .60-$1/sq. ft. to have R49 insulation blown in. If you use cellulose insulation you may also qualify for various green energy incentives and federal tax credits as well, lowering the project cost even further.

Fiberglass batt insulation

Fiberglass batt insulation comes in large rolls, with pieces cut to fit the area to be insulated. Batts have a stiff paper backing on one side that is often stapled down to framing and joists to hold the insulation in place.

Batt insulation is typically cheaper than blown attic insulation and the only tools necessary to install it are a utility knife for cutting the insulation and a staple gun for securing the batts. A respirator, gloves, and eye protection are also highly recommended when working with fiberglass batt insulation, especially when working in a confined space such as an attic.

Fiberglass batt insulation can typically be purchased for .40-.75/sq. ft., so it can provide some cost savings as opposed to blown-in attic insulation, and batts do provide a slightly higher R factor for the same amount of insulation. For the homeowner willing to spend some long sweaty hours working in a hot attic, batt insulation may be the way to go.

Using Closed Cell Spray Foam in an Attic

One area that this material is also very useful is in the perimeter of the attic where the wall meets the rafters.

Spray foam insulation is a great form of insulation if used for air sealing and insulating walls, box sills, and slanted ceilings. One area that this material is also very useful is the perimeter of the attic where the wall meets the rafters. This area is often the worst insulated because there is simply not enough depth at the edge of the attic to add adequate insulation. This has been corrected in recent years with trusses that have energy heals that accommodate for the proper insulation depth.

However, most existing homes do not have this option. This is where using the spray foam can give your home the extra R-value and air sealing you need to prevent the airdrop from the edge of the attic.

For this type of insulation method to work, the ventilation still needs to be part of the attic area. Using specially designed cardboard chutes that fit into place and are stapled to the top plate of the walls between the roof rafters, ventilation can be maintained while the extra R-value is added. The chutes allow the insulation to be added completely over the top plate of the wall which is how the insulation is supposed to be installed. The spray foam is then applied over the top plate at a depth of 3 to 5 inches depending on the amount of room available.

Important Air Sealing Points

It is very important when using the spray foam insulation along the attic perimeter that the insulation be sprayed onto the edge of where the drywall meets the framing. This is an extra precaution that will all but eliminate air infiltration around the edge of the home.

While in the attic it is also a good idea to seal all plumbing, electrical, and chimney penetrations that are present in order to prevent air from following these pathways into the house as well. Keep in mind that when you shut off one air pathway into a home, it can magnify other air pathways so it is important to be diligent in properly air sealing everything.

Most air sealing can be performed with can foam. The perimeter spray foam, however, should be performed with a 600 board foot kit set for a higher grade foam and installation.

Finishing the Project

It is extremely important to replace the insulation back the way it was after you have performed the perimeter spray foam insulating. This will make the thermal blanket in the attic consistent and allow for the maximum efficiency out of your current attic insulation.