Understanding Attic Insulation

Today’s rising energy costs are leading to an increase in energy-saving home improvements such as attic insulation, window replacement, wall insulation, etc.  If you are considering taking on one of these projects, make sure you first understand the facts!

When considering attic insulation, remember that not all types of insulation perform the same.  The three most common types of attic insulation are: traditional fiberglass, blown-in cellulose and spray foam insulation.  (Spray foam insulation is better at sealing against air infiltration from the outside, and is mainly used for insulating stud walls.)  For attic insulation, professionals are using either rolled-out fiberglass, or blown-in cellulose.

Attic floor insulation is vital to a comfortable, energy-efficient home.  The goal, in the winter time, is to keep the heat that your furnace produces within the envelope of the home.  Since heat rises, the majority of heat lost within the envelope is not lost through the walls, but through the ceiling and into the attic.  Attic ventilation plays a significant roll in this process as well.  If the attic’s exhaust ventilation exceeds the amount of intake ventilation, then the exhaust components (ridge vents or can vents) will draw their intake from the envelope of the home, literally pulling warm air from the home only to be exhausted through the vents!  Proper attic insulation will help to keep the warm air in the envelope in the winter, and keep hot air building up in the attic during the summer from radiating through into the living spaces below.  Read our article: “Tips about Roofing and Attic Ventilation” here.

When choosing the right type of attic insulation for your home, you should understand the math behind your options.  Insulation is rated by an “R value” (R stands for resistance); the higher the R value, the more resistance to heat transfer, and therefore a better insulator.  Traditional fiberglass insulation has an R value of around 3.2 per inch, while blown-in cellulose has an R value of 3.9 per inch. Blown-in cellulose is more energy efficient because it creates a monolithic blanket, whereas fiberglass leaves gaps where heat can still seep through and into the attic. For northern climates, such as Michigan, Energy Star recommends a R-55 for attic insulation. 

What does this mean for you?  First determine how much insulation you have currently.  Most homes today have at least 5″ of fiberglass rolled out on the attic floor  So for example, if you have 5″ of fiberglass, you have about R-16 currently.  So to reach R-55, you would need to add at least 10″ of cellulose (R-39).  Most professionals will exceed the minimum amount by a couple of inches to account for settling of the cellulose over time.  Cellulose will rarely settle more than an inch or two over a period of 10 years.

The most common mistake made when blowing in attic insulation is poor preparation.  Professional installation should include boxing off/around things in the attic such as recessed lighting, vents, duct work, etc.  This will prevent the cellulose from falling through the ceiling into the living spaces below.  Also, make sure baffles are used to prevent the cellulose from covering intake ventilation for your attic (usually at the soffit).  The last thing you want to do is to suffocate your attic; you need to maintain a constant flow of air along the entire underside of the roof decking.  If you don’t install baffles when blowing in cellulose, you risk blocking the flow of air into your attic.  This can result in premature shingle deterioration, shingle curling and mold/moisture issues in the attic.

To talk more about your specific attic insulation needs, call Kopke today at (586) 777-6633.