Ventilation is a good thing in an attic. What it does is move hot air that tends to accumulate in an attic out of this space. The result is roof structures better protected against condensation and moisture issues and a space better suited for use as an additional living space. If your goal is to find the best insulation for a vented attic, we recommend three possibilities:
- Spray foam insulation
- Mineral wool insulation
- Cellulose blown-in Insulation
About Ventilated Attics
When installing insulation in a vented attic, you’ll want to be careful not to block sources of ventilation. As for what a vented attic is, it’s simply one with a ventilation system in place that allows for sufficient airflow. The main components and features of an attic ventilation system include:
- Intake vents: These are vents placed in the lower part of the roof just below the eaves. Intake vents allow cooler air to get into your attic.
- Hot air exhaust vents: These vents are placed within the peak of the roof in your attic space. They allow hot or warmer air within your attic to get out.
- Rafter venting: Installed in rafter spaces, this type of ventilation allows air to flow through soffit vents in a way that doesn’t affect the overall aesthetics in a finished attic.
Where to Install Attic Insulation in a Vented Attic
As for where to install attic insulation, avoid covering any of your vents. Doing so will prevent hot air from getting out of your attic and block the intake of cool air. You’ll also want insulation placed adjacent to eave and soffit vents to prevent heat loss/air transfer in these areas. You can also insulate up to the edge of the attic floor. Other spaces can be insulated as well, just as long as you are mindful of vent locations.
Spray Foam Insulation
Spray foam is a two-part type of insulation. It’s created by blending isocyanate and polyol resin into a foam material that solidifies or “cures” when it hardens. Spray foam is appealing in attics since it provides a tight seal once it cures. It also fits well into hard-to-reach spots. There are two different versions of spray foam insulation:
- Open-cell: More spongy, this type of spray foam is excellent for absorbing sound.
- Closed-cell: More solid and rigid, this version of spray foam is greater in density and provides a higher R-value.
Spray Foam’s R-Value
R-value is a measure how well insulation blocks the transfer of heat. The R-value of open-cell spray foam is 3.7 per inch. Closed-cell spray foam has an R-value that could get as high as 6.5 per inch.
How Spray Foam Is Installed
The most effective way to install spray foam in your vented attic is to purchase a kit that has everything you’ll need in it, or to have it professionally done. If you’ll be doing it yourself, make sure you have the right gear/equipment first. These items include:
- Full protective suit
- Gloves that are chemical resistant
- Eye protection that wraps around
Next, cover windows and other openings in your attic with plastic. Also, do the same thing with your attic vents. Once spray foam hardens, you’ll need to scrape it off. One other step you’ll want to take before getting started is to make sure places where you’ll be spraying are dry. Spray foam doesn’t adhere to wet or damp surfaces well.
With application, start with the edges. This allows any small gaps or spaces to be properly covered and sealed. After the outer areas dry, fill in the rest of the inner areas with spray foam. This type of insulation is best applied in 2-inch layers. If you need another layer, wait for the first one to cure. Any excess spray foam can be scraped or cut off.
Mineral Wool Insulation
Also called rockwool, mineral wool is so-named because it’s made from stone, volcanic rock known as basalt, or industrial waste, which is also called slag. These materials are spun at very high temperatures and turned into batts similar to what’s common with fiberglass insulation.
Mineral Wool’s R-Value
Mineral wool in batt form has an R-value that ranges from 3.1 to 3.4, although some rockwool products have a slightly higher R-value. Blown mineral wool has an R-value that ranges from 3.1 to 4.0
How Mineral Wool Is Installed
You’ll also need gloves, safety glasses, and a mask or respirator to install mineral wool in your attic. In batt form, it’s simply put into place and cut as necessary. If you have mineral wool with no vapor barrier (unfaced), friction will keep it in place. However, if it’s faced, you’ll need to staple it in place. Unlike fiberglass batts, mineral wool does not really need an additional vapor barrier to produce the intended results. This is because mineral wool is denser and has good water resistance properties.
Cellulose Blown-In Insulation
If you go with blown-in insulation for your vented attic, the most common material of this nature is cellulose. Cellulose typically consists of recycled wood-based materials specially treated with chemicals that make it resistant to fire and mold.
Cellulose Blown-In R-Value
The R-value of loose-fill or blown-in cellulose ranges from 3.2 to 3.8 per inch. This is higher than what’s common with loose-fill fiberglass.
How Cellulose Is Installed
In order to install blown-in cellulose, you’ll need a mechanical blower or hopper. You should be able to rent one at a local hardware or home improvement store. This fluffy insulation material is then blown into place with a hose attached to the blower. The application process can be easier if you have a helper to keep loading the hopper with more loose-fill cellulose. Blow it where you wish to apply it in your attic. Just be mindful of your attic vents so you don’t clog them with blown-in cellulose material