How To Insulate A Vaulted Ceiling

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A vaulted ceiling, also known as a cathedral ceiling, makes for an exceptionally beautiful home. A cathedral ceiling adds grandeur to the room and can make the space appear bigger, roomier, and more luxurious. The downside of a cathedral ceiling is that they leave too much space between the ceiling and the actual room. As such, the ceiling temperatures often tend to be much lower than the room temperature, and that makes your AC work extra hard and, as a result, runs up your electric bill.

To insulate a vaulted ceiling, it needs to be built to allow for the insulation work to occur. In addition, it needs to have enough space between the roof deck and the actual ceiling for both roof ventilation and insulation. Vaulted ceilings built this way have scissor truss framing, truss joints, or much larger rafters. In this case, the best approach when learning how to insulate a vaulted ceiling is to use batted insulation like you would with a typical ceiling.

What About Unvented Cathedral Ceilings?

There’s another vaulted ceiling design that is typically referred to as an unvented or hot roof design. This is the kind of design that doesn’t give you the high beams or truss framing as you would expect in a typical vaulted ceiling.

While the term “hot roof design” means that the type of cathedral ceiling typically runs warmer than its counterpart, it is a little misleading. The temperature difference is hardly ever more than 1 or 5 degrees Fahrenheit on the surface compared to a normal roof.

In this case, however, the insulation can be installed by directly attaching it to the roof sheathing, meaning that there will be no ventilation. This kind of insulation is not being done using cellulose or fiberglass as building codes across the country forbid it.

Step-By-Step Guide On How To Insulate A Vaulted Ceiling

The important thing to note here is that the type of insulation you use will depend on the type of vaulted ceiling you have. Generally, you will find that all you need to do is lay down insulation batts over your roof rafters if there’s space. In this case, you will need to leave at least two inches of breathing space between the roof sheathing and the insulation to allow for proper ventilation.

In many cases, you will find that using foil-faced batt insulation is the best approach for cathedral ceilings. Since this is the most common type of insulation when dealing with vaulted ceilings, let’s take a quick look at how you can get it done.

Step 1: Accurately Measure The Area To Be Insulated

This is the first step in every construction project – you need to accurately represent how much space needs work. In this case, take accurate measurements of the distance between the rafters or trusses.

Once you have that number, multiply it by the number of spaces to get just how much insulation material you will need. Once you have that number, go ahead and purchase the kind of insulation you deem fit based on the recommended R-value for your location.

Step 2: Roll Out The Insulation

Once you have the insulation you need, roll it out over the appropriate workspace. Since this is a continuous sheet of insulation, you might want to cut it up into a few appropriate pieces to make it manageable. If you take this approach, make sure that the separate pieces fit snuggly against each other instead of being crammed against each other. When you cram insulation material against each other, its R-value reduces.

Step 3: Place The Cut Strips Appropriately

Foil-faced batt ceiling insulation has a foil side that acts as a vapor retarder. In most states, you are required to place this vapor retarder side down unless the building codes in your area specify otherwise.

Once you’ve done that, all you have to do is staple the flanges to the insulating material to the bottom of your roof trusses. Make sure that the insulation is pulled tightly, so it’s snug while doing so.

Step 4: Make Allowances

While laying down layers of insulation to your vaulted ceiling can make for a challenging yet interesting DIY project, one of the main reasons many homeowners prefer hiring a professional to get the job done is because of all the other aspects involved, such as tampering with electrical wiring.

If you are confident in your skills, this shouldn’t be that much of a problem. However, if not done correctly, it can present future fire hazards or the risk of electrocution during the project. Therefore, you have to be very careful when maneuvering the ceiling insulation material around such fixtures.

Step 5: Use Wire Support

To secure the gaps in insulation, use wire support designed to perpendicularly secure the insulation to the trusses.

One thing you need to remember about this kind of work is that safety comes first. Any time you want to work on your cathedral ceiling, you need to wear protective gear such as gloves, long sleeves, goggles, masks, and even a helmet.

You also need to pay very close attention to the building codes in your area and check with your local municipality before adding cathedral ceiling insulation just in case there are permits involved. This information will also help guide you towards the best kind of insulation to use on vaulted ceilings in your local area.

That being said, these are the steps to follow to learn how to insulate a vaulted ceiling. As mentioned above, however, these types of ceilings are tricky and might require the help or, at the very least, the guidance of a professional contractor.

Frequently Asked Questions

What’s the best insulation for a vaulted ceiling?

Generally speaking, you may find that a closed cell foam will be the best choice if you have an unvented cathedral ceiling to insulate. However, closed cell foam is also one of the more expensive insulation material options. Foil-based insulation is also a good choice as it can be a more cost-effective solution for a cathedral ceiling as well as a finished attic.

What R-Value do I need for a vaulted ceiling?

The minimum R-Value you can have for a vaulted ceiling is R-30. Keep in mind that you can’t reach this value with fiberglass insulation. You are required to have a two-inch air gap between the insulation and the plywood to ensure proper roof ventilation, leaving you with only 3.5 inches.

Should I put a vapor barrier on my cathedral ceiling?

A vapor barrier should only be installed in vented attics where a climate has more than 8,000 heating degree days. 

Can you use spray foam insulation on a vaulted ceiling?

Fiberglass batt insulation was one of the only ways to insulate a vaulted ceiling at one time. However, over time, these fiberglass batts began sliding out of place, compromising the home’s energy efficiency. So, if you are looking for an alternative to fiberglass insulation for a vaulted ceiling, spray foam insulation can be used and can address the R-value and moisture management.