How Much Insulation is Needed?

What’s the best attic insulation? That depends on your definition of “best”. Your insulation contractor will tell you what’s going to perform the best is definitely not the most cost-effective way to insulate an attic. But surely, you already knew that.

First, let’s discuss the most common types of insulation available for attics; spray foam, loose-fill fiberglass, cellulose, and fiberglass batts. Those aren’t the only types available, but they make up the vast majority of what’s used in Minnesota attics. For the listed R-values below, this refers to the material’s ability to resist the transfer of heat and is all per-inch. The higher the number, the better. The minimum R-value for a new Minnesota attic is R-49.

How Much Attic Insulation Do I Need?

If you think you’re among the 90% of US homes that are under-insulated, 1 performing a simple insulation inspection will help you determine your insulation needs. Having the correct amount of attic insulation can help you maintain a comfortable temperature throughout your home and help save money on your energy bills*—plus, prevent major issues like ice dams in the winter.

Inspecting your attic insulation

First things first, you need to go up into your attic, inspect the condition of the insulation, and calculate the current level of insulation. Your attic should have a certain amount of insulation in it, and the recommended level of insulation for your attic is dependent on where you live.

Seal air leaks

Pull back the existing insulation and use expanding spray foam to seal any gaps around plumbing pipes, ceiling perforations and holes where electrical wires snake through. “Make sure to seal all the way around the pipe, ” says Olson. For gaps 1/4 in. or less, use caulk rather than expanding foam.

Leaks from cracks and gaps around lights, plumbing pipes, chimneys, walls and other ceiling penetrations are the equivalent of having a 2-ft.-wide hole in your ceiling. The worst offenders are open stud and joist cavities and dropped soffits and ceilings in kitchens and baths 

Add vents

Pull the existing insulation away from the roof. Position the new vent chute so the bottom extends 6 in. into the overhang and staple it into place. Olson suggests using a squeeze stapler instead of a hammer stapler. “It’s more accurate and there’s less chance you’ll crumple the chute.”

“In 95 percent of the homes we work on, the vent chutes are missing or aren’t properly installed, ” says Olson. Without them, you’re not getting the most out of your insulation’s R-value because air needs to move properly at the eaves to remove moisture in the winter and heat in the summer.

To make sure existing chutes aren’t blocked, stand in a dark attic to see whether light from the eaves is filtering through the vents. Replace any chutes that are blocked, damaged or missing. You’ll find both plastic and foam vent chutes at home centers. Olson recommends using foam chutes. “They’re more rigid and there’s less chance of them getting crumpled or compressed when you’re installing them.” Pull back the existing insulation so you can see out to the edge of the eaves, and install a vent chute in every rafter space.

 

 

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