Blown-In Insulation Basics
One of the best ways to reduce energy bills is to add insulation in your attic. In fact, increasing attic insulation is often the single most important step you can take to save on heating and cooling expenses. Often, the easiest way to add insulation to an unfinished attic is to blow in loose-fill cellulose or fiberglass insulation.
Cellulose is preferred for a few reasons. It is an environmentally responsible material made from recycled newspapers. It is less expensive than fiberglass and has a higher R-value and is less irritating to the skin and lungs. Also referred to as "natural fiber insulation," cellulose is sold compressed in large plastic bags at home improvement stores. The bags need to be emptied into a blower, which in turn sends the fluffed-up insulation through a long hose. You can usually borrow a blower or rent one for a minimal fee from the same store.
A blown-in insulation job requires two people, one to keep the blower full and working and the other to work the hose in the attic. But the important task of preparing the attic is something you can handle on your own.
Air-Seal Before Insulating
Older houses allow lots of air to leak through ceilings into the attic. During summers and winters, that lost air is lost money since you paid to heat or cool it. So the first task is to seal the leaks. This step will cut energy losses even if you don't bother with blown-in insulation. Air leaks can occur around the following items:
Before heading into the attic, make a map of these potential leak spots downstairs. Use the map to guide you in the attic.
Lay some plywood or boards over the floor joists to provide a temporary walking surface. Take care not to step between the joists, as you will likely put your foot through the drywall ceiling below.
If there is already some insulation in the attic, you will need to pull it out of the way while sealing leaks. Use expanding spray foam around gaps 1/4-in. wide or larger, and use caulk for smaller gaps. Completely fill all gaps.
If your house has soffit vents in the eaves, check to see that there are vent channels over them in the attic. If not, or if the existing ones are damaged, install new channels to allow air to circulate properly under the roof. You will need channels in every rafter space that is ventilated. Use a stapler to attach the channels to the roof deck.
Determine the Insulation R-Value Needed
Determine the depth of blown-in insulation you will need. The depth will depend on where you live and the R-value of the insulation you use. Cellulose typically provides R-38 at a depth of 10 inches.
You can determine the level of insulation needed by checking the map provided by the Department of Energy or get a specific recommendation using a Zip Code Insulation Calculator.
Use a tape measure and permanent marker to mark the required depth of blown-in insulation on vertical truss members or wall studs around the attic space. Be sure to measure from the drywall surface, not from the tops of the joists.
If you already have some insulation in the attic, determine its R-value and subtract that amount from the total desired to determine how much new insulation will be needed.
Get the Cellulose Insulation and Blower
Buy a few more bags of cellulose insulation than you think you will need. You should be able to return the unused bags, and it will save you from having to make a quick trip to the store if you run out of insulation before you finish.
As an example, GreenFiber Blow-In Natural Fiber (Cellulose) Insulation comes in bags that measure 12 by 15 by 24 inches. To achieve R-38 in an attic with no existing insulation, you would need 60 bags of cellulose insulation for every 1,000 square feet of surface to be covered. Lowe's and Home Depot provide free blower rental (including 100 feet of hose) if you buy this quantity of insulation.
Prepare the Blower Equipment
This now becomes a two-person job. One person needs to feed the blower, while the other handles the hose in the attic. Be sure to read any instructions that come with the blower. Fill the hopper on the blower about 3/4 full, and then turn it on.
Break apart the compressed material as you load it, but keep your hands outside the hopper. Some blowers have a sliding gate that is used to control the flow.
Blow in the Insulation in the Attic
The person working the hose should start at the far end of the attic and work back toward the access hatch. Keep the hose horizontal, about 2 feet above the attic floor. You should be able to fill about three or four joist bays from one position. You may need to push the hose into the eaves. You can also use a broom handle to push insulation into hard-to-reach spaces.
Using a sweeping motion, spread an even layer of insulation up to your depth markings. Always blow in the same direction as the joists. Over time, the insulation will probably settle an inch or two.
If the blower clogs, turn it off, unplug it, and clear the insulation from the hose and hopper before proceeding. Refill the hopper as needed. Continue the same process until the entire attic floor is filled up to your depth markings. If desired, you can insulate the backside of the attic hatch cover with a thick layer of rigid foam insulation board or a piece of cellulose batt insulation.