One of the most important thermal barriers in the average home is the layer of insulation on the attic floor. During the winter, this insulation prevents heated air from rising through the top floor and into the attic, and during the summer, it prevents superheated attic air from seeping down into your rooms. This makes attic insulation important in any climate.
In cold temperatures, insufficient attic insulation is a major contributor to the “chimney effect”, which drives up heating bills and makes homes feel drafty. The chimney effect occurs when hot air escapes quickly through the attic, creating a vacuum that draws cold air in through air leaks in the basement and ground floor. Once this cycle gets going, it can make your furnace run around the clock while preventing your home from feeling truly warm.
You might already be aware of some warning signs that your attic insulation isn’t up to snuff. If the highest floor of your home feels too warm during summer days or too cold during winter nights, that’s reason enough to check out your insulation. And if you notice lots of icicles and ice dams on your guttering, that’s a dead giveaway -- it’s a sign that warm air is seeping into the attic and melting roof ice from underneath, where it refreezes on the cold gutters.
If your attic insulation needs upgrading, make a plan to add more insulation soon. As the energy savings add up, it will eventually pay for itself.
Look, Measure, Audit
It doesn’t take a trained eye to determine whether you need more insulation. All you need is a yardstick or tape measure, and maybe a flashlight if you don’t have adequate lighting in the attic.
From the attic hatch, look around in every direction. If you can see the floor joists - boards about eight inches high spread a few feet apart across the attic floor - you probably need more insulation. Whether you have batt insulation (fluffy blanket-like material) or loose fill (shredded material), there should be enough to completely cover the joists.
Your insulation’s “R-value” is a measurement of its effectiveness. Homes in cold climates should have an R-value of at least R-49 in the attic, and in warmer climates, R-38 is recommended.
How to calculate the R-value of your insulation
- Measure the thickness of your attic insulation. The depth in inches is half of the information you need to determine your insulation’s R-value.
- Find out what type of insulation you have. This is fairly easy because common attic insulation types have different colors: fiberglass is pink, cotton is blue, cellulose is gray and rockwool is yellowish-gray. Loose fill cellulose and rockwool can be tricky to tell apart, so you may need to take a sample with you to the hardware store and ask an expert.
- Multiply your insulation thickness by your insulation's R-value. Each type of insulation has its own R-value per inch. Use this table to finish calculating your R-value:
|Fiberglass batts||2.9 - 3.8|
|Fiberglass loose fill||2.2 - 2.9|
|Cotton batts||3.0 - 3.7|
|Cellulose loose fill||3.1 - 3.8|
|Rockwool batts||3.3 - 4.2|
|Rockwool loose fill||2.2 - 3.3|
Add Airflow with Rafter Vents
Before you can start adding insulation, there’s one more step you may need to take: adding rafter vents. Sometimes called rafter baffles, rafter vents help ensure proper attic airflow while allowing you to extend your insulation right up to the eaves. They’re usually about four feet long and slide into the gaps between the rafters to keep a channel of open air between the attic and the soffit vents, which are hidden behind rain gutters. Without rafter vents, your attic may get too warm, leading to ice dams in the winter and roof-damaging temperatures in the summer.
Measure the space between your rafters to make sure you’re buying a size that will fit. Rafter vents can be stapled directly to the underside of the roof.
The Choice is Yours
You don’t have to add the same type of insulation you already have in your attic. Different materials can be used together, as can batt and loose fill insulation. With this freedom and your R-value calculations, you can shop for insulation based on the lowest price. But keep in mind that loose fill insulation requires a special blowing machine to spread the material around your attic, and this will have to be rented at an added expense. Be sure to obtain detailed instructions on the use of the blower if you go this route.
Batt insulation is easier to work with and can simply be unrolled over the existing insulation. As long as your existing insulation reaches or exceeds the top of the floor joists, it’s best to unroll the new layer perpendicular to the joists. This will maximize your insulation efficiency by covering the joists on all sides.
DIY or Hire a Pro?
If you conclude that you need more attic insulation, you may be able to get the job done yourself. It’s not rocket science, but it is physical work that will involve lots of kneeling and moving around all areas of the attic. Attention to detail can also make a big difference in the effectiveness of this upgrade, so there are valid reasons why you may want to hire a professional to complete this work.
There are a few other factors that can justify calling in an expert. If you have a leaky roof or signs of mold on your insulation or joists, you’ll need to patch the leak and completely remove the mold before adding new insulation. And if you discover any vents that exhaust directly into your attic, such as from a bathroom, kitchen range or clothes dryer, those should be rerouted out of the home before you proceed.
If you have a professional assess your attic insulation, you might want to schedule an energy efficiency audit. This is a service in which experts use specialized tools to inspect your entire home for efficiency problems like poor insulation, air leaks and HVAC problems. A well-done audit will conclude with a detailed written report that explains all the upgrades you can undertake to make your home more comfortable and efficient.
But if you’re confident you can handle it, keep a few safety tips in mind. You should wear a hard hat, safety goggles, gloves and long sleeves when working with insulation in the attic. Knee pads will also make the job much easier. If you’re working during hot weather, take frequent breaks and drink plenty of water to keep cool. Most importantly, be careful to only walk or kneel on the joists and not on ceiling drywall, which won’t support your weight!
Whether you hire a pro or make it a weekend project, beefing up your attic insulation might be your best opportunity to improve your home comfort and lower your utility bills. But insulation is just part of the package - to maintain or upgrade your HVAC system, thermostat, ductwork and more, let a licensed HVAC technician show you how you can get the most out of your home.