Attic ceiling insulation
Do it yourself or hire a pro?
Attic ceiling insulation can cut your heating bills by more than just about any other home energy upgrade. Let's look at the different choices for attic insulation, from blown to batt, and from cellulose to fiberglass and rock or mineral wool.
We'll cover recommended attic insulation levels, the importance of ventilation, how to make sure your contractor installs the right amount of blown in insulation, and health risks associated with vermiculite attic insulation.
Before you undertake any major attic energy efficiency upgrade, it's a good idea to do a comprehensive energy audit yourself to figure out where you can maximize your home energy savings. Sometimes a small investment up front and a bit of your own time to determine where your energy dollars are going can save you hundreds of dollars on unnecessary or less than optimal energy efficiency upgrades.
Before we get to the main topic ... a primer on attic insulation and R-values!
How does insulation work?
Insulation works by trapping tiny pockets of air or other gases between insulating solids such as fibers or foam. This combination of air and solids impedes the flow of heat through a space, by stopping heat conduction (heat transferred through solids or liquids, in this case the solid of the fiber or foam).
Because the air pockets are so small, insulation also stops convection, which is heat transferred through liquids or gases, in this case the air trapped in the fibers, or the air or gas trapped in the foam.
Heat does eventually make its way through the insulation, traveling from the warmer side to the colder side, but the better the attic insulation, the longer it takes heat to move through it. And don't forget that, because heat rises, a lack of attic ceiling insulation means you'll lose a lot more heat than for an equivalent wall space with no insulation.
What are R values?
The R value of insulation material is a measurement of how effective the insulation is at slowing down the natural transfer of heat from the warm surface to the cold surface.
R value is a function of the amount of heat transferred through an area, given a temperature differential. Since each of these three quantities can be specified in Imperial or metric measurements, R values are different between North America and the rest of the world, with Imperial (North American) values being approximately5.67 times the metric values. In this article we will stick with North American R values.
You can generally add together the R values of different materials added together. For example, if you have attic ceiling insulation consisting of 10 inches of fiberglass batt insulation between joists at R-3.14 per inch (total of R-31.4), and you blow in another 5 inches of fiberglass insulation at R-2.5 (total of R-12.5) your total insulation becomes R-43.9. The only problem with this rule is that the thicker the insulation layer, the more the upper attic insulation compresses the insulation below it, reducing its R value.
Attic blown in insulation vs. batt insulation: installing attic insulation
You can install your own attic ceiling insulation if you choose batt insulation for attics. Batts are intended to fit between the joists of your attic ceiling. They should not be installed over top of existing attic blown in insulation.
If you already have attic blown in insulation, your best bet is to hire a professional to top up what you already have. On the other hand, if your attic blown in insulation is damaged due to a leaky roof (for example, pressed down by shingle grit or bits of roofing wood), it may make more sense to remove it and install new insulation, either blown-in or batt. Just make sure you redo your roof first!
Batts have a higher R value per inch if installed correctly. Correct installation means you have to be very careful to ensure there are no seam gaps between batts, and to ensure you don't compress the batts when installing them. Loose-fitting batts mean heat will escape through the air spaces in the insulation, and compressed batts mean the R value is significantly reduced.
Attic blown in insulation can be installed much more quickly, by a professional, and can be installed over top of either existing attic blown in insulation or batt insulation, and you don't have to get dirty yourself. If cost is a real factor for you, you should still consider getting quotes from an insulation company or two for attic blown in insulation, and compare that with your own estimate of do-it-yourself insulation. You may be pleasantly surprised - installed attic blown in insulation is often cheaper than batt insulation purchased from your local building center, and that's before you've installed the batts!
There are a couple of ways to add batt insulation to attic blown in insulation if you can't afford to hire a company to help. Suppose you have 8 inches of blown in insulation (we'll assume that's R-2.2 per inch, or R-17.6) and you want to have at least R-30 everywhere:
- Take a rake into the attic and rake all the attic blown in insulation into an area equal to one half of the attic minus one joist width. Clear every last scrap of blown in insulation from the cleared section. Mound the insulation
- Install R-30 or higher batts (10 inches at R-3.14 or higher per inch) in the half of the attic where you removed the blown in insulation (leaving the one joist closest to the mounded insulation empty)
- Use your rake again to level the blown in insulation and remember to fill in the empty joist between the batt insulation and the mounded blown in insulation.
Alternatively, if the attic blown in insulation just covers to the level of the top of the joists, you can add batt insulation over top by placing the batts crosswise to the joists. Just remember not to leave any airspace between batts.
When installing insulation yourself, be sure not to cover up any ventilation channels in your roof surface or soffits.
What R-value do I need for attic insulation?
The higher the R-value you use to insulate your attic ceiling, the more energy efficient your house will be. Don't skimp on this expense! In general, in extremely cold areas such as most of the Canadian prairies and north, and the northern US plains states, you should strive for R-49 or higher, and even the southernmost parts of the US should strive for at least R-19 (remember, attic ceiling insulation not only helps hold the heat in during cold weather, it slows the heat entering your house from your attic in hot weather).
The following map shows heating zones for the US, where recommended attic ceiling insulation levels for natural gas, heat pump, or fuel-oil heating are R-49 for zones 1-3, and R-38 for zones 4-6. For electric heat, R-49 is recommended for all zones. For zone 6, gas only, R-22 is acceptable but R-38 is preferable. Remember that these are minimum recommended levels; more is almost always better.
Figure: Attic ceiling insulation map for US heating zones. Source: EERE Energy Savers: Insulation.
For electric heat you should always install as much attic insulation as possible, because even the most energy efficient electric heat is more expensive than natural gas, oil, or wood stove heat. Strive for at least R-49 regardless of the zone you live in.
The importance of ventilation
Make sure you or your installer do not cover up any existing attic ventilation, from roof vents, side wall vents, or soffit vents, when installing attic ceiling insulaiton.
In fact, when you are reinsulating your attic it's a good time to consider adding ventilation to soffit vents if you do not already have enough (you can never have too much roof ventilation, as long as you don't let water in!).
For soffit vents, install cardboard or rigid plastic ventilation baffles, available at your building center, from the soffit vent up along the roof line so that the top of each baffle clears the top of the added insulation.
Adequate ventilation helps keep your attic from getting too hot in summer, and keeps a good airflow to prevent humidity build-up in cooler weather. One smart solution is to install a solar powered attic vent. These vents use a small solar panel, in some cases along with wind power that turns the vent itself, to exhaust heat from your attic. Because solar power is strongest on hot sunny days, these solar attic fans help keep the attic cool on such days.
Checking the installation of attic blown in insulation
If you are half-way handy and are having insulation blown in by the pros, nail a few thin strips of wood upright against the joists so that they reach at least 8 inches above the level of attic ceiling insulation you're paying to have blown in. Then mark the level of agreed insulation (measuring from the top of the ceiling between joists, not the top of the joists) with a red permanent marker, and mark lines two inches above and below that line. That way, you can climb up into your attic when the job is done and check whether the installer got the correct level of insulation. If there are a few areas that are below the red line, don't worry too much as long as they aren't below the lower black line. These markers will also remind your installer to do a thorough job - when they know their work is being measured, they tend to be more careful.
What's the best attic insulation?
There really is no single type of insulation that is the best attic insulation. Avoid rigid or sprayed foam insulation in attics, as you do not want a vapor barrier between your attic and your living space, and foam panels provide some level of vapor barrier, while sprayed foam creates a total vapor barrier. Blown in fiberglass or cellulose, or fiberglass batts (such as Pink Panther insulation), or rock wool batts (such as Roxul) are all suitable materials. The key considerations are R value per inch, and inches installed. Typical R-values for different types of insulation are:
|Insulation Materials||Typical R-value range|
|Fiberglass Batt (e.g. Pink Panther insulation)||3.14-4.30|
|Fiberglass Blown (attic)||2.20-4.30|
|Rock Wool Batt||3.14-4.00|
|Rock Wool Blown (attic)||3.10-4.00|
|Cellulose Blown (attic)||3.13|
See note below on vermiculite - I do not recommend using it anywhere in your home.
Vermiculite attic insulation
Vermiculite is a naturally occurring mineral which expands into a very lightweight material when heated. Vermiculite pellets were commonly used to insulate attics until the 1990's. Vermiculite was thought to be harmless, and indeed in its pure state there are no health risks posed by vermiculite.
However, one of the main mines where vermiculite was mined until 1990 was a mine near Libby, Montana, which also contained a natural deposit of asbestos. As a result, vermiculite from this mine became contaminated with asbestos. The mine was shut down and current sources of finished vermiculite are low in contaminants. However, due to both the low R-value of vermiculite compared to other blown or batt insulation, and to ongoing concerns about contamination (even at low levels), I would suggest avoiding it altogether.
Zonolite insulation, a brand manufactured by W.R. Grace & Co until the early 1980's, is one type of attic insulation made from vermiculite. Zonolite insulation originated from the Libby mine, but the manufacturer claims that its manufacturing process removed most of the asbestos fibers and that the resulting product posed no significant health risks. Zonolite insulation was discontinued for economic reasons only.
However, there are an estimated 15 to 35 million homes in the US with Zonolite insulation installed in their attics or walls. As a result of a class action lawsuit against W.R. Grace, homeowners with Zonolite insulation installed can apply for a rebate of 55% of removal and remediation costs of the insulation, provided the work is done by certified professionals, up to a maximum rebate of $7,500.
If you do have Zonolite insulation or other vermiculite attic insulation installed already, do not disturb it and avoid going into the attic at all. You are unlikely to experience any health issues if the insulation is left in place undisturbed and you stay out of the attic. The real risks come when you breathe the attic air or disturb the vermiculite attic insulation by entering the attic.
If you are unsure whether you have asbestos insulation in your attic, see the information at the Asbestos network on How to check for asbestos in my home. Although you can gather samples to send in for testing for asbestos content, even the act of gathering the insulation sample can be hazardous so read up first.
If you need to do a ceiling renovation that requires insulation to be moved or removed, hire a licensed asbestos insulation removal company to test, and if necessary remove, the vermiculite attic insulation. Asbestos is an extremely toxic compound whose ill health effects can take years or decades to show up.