How To Insulate An Existing Flat Roof

Still interested to know more about insulating an existing flat roof? Continue reading as we discuss other related topics like cold rood insulation, materials used, interior vs. exterior insulation, and many more. We will also provide some cool and informative articles at the end of this post, so go on and finish reading to learn more!

Two identical residential houses painted in white with a flat roof, How To Insulate An Existing Flat Roof

There are multiple ways to insulate an already existing flat roof. Some are simpler compared to others, while some would require a complete renovation of your roofing. So let's dive right in to learn more about these methods.

Three story modern residential home painted in brown

Outer rigid foam insulation

This type of insulation installs a thick layer of hard foam, usually about six inches thick. It is placed ab0ve the roof sheathing. This type of insulation does not require your roof to be taken down as it is only placed above it. 

It helps in insulation by being the primary receiver of the heat from the sun, effectively blocking it from penetrating through the roof, the attic, and the inside of the structure. The foam placed on top is designed to contain the heat and prevent it from going through. 

Outer rigid foam combined with interior insulation

This type of insulation is similar to the first one. The only difference with this insulation is that it has another below the roof heating. The exterior foam used in this is slightly thinner at 2-4inches and is coupled with air-permeable insulation underneath the roof sheathing. 

You can use blown-in fiberglass or cellulose as your main insulator for the interior. You can place this in direct contact with your roof sheathing. And since it has interior insulation, you might need to remove some parts of your roofing to install your internal insulation directly.

Outer closed cell-foam insulation

Exterior closed cell-foam insulation is done by spraying a layer of foam called closed-cell polyurethane on top of your roof sheathing. But before that, a layer of air-permeable insulation is sprayed as a first layer directly on top of the roof sheathing. 

This insulation requires no structural changes at all and only needs spraying. This is like painting your roof, but instead of only adding colors to it for aesthetic purposes, you are adding insulation to help regulate the temperature inside your structure. 

Inner closed cell-foam insulation

Now, this is the opposite of the outer closed cell-foam insulation. Instead of spraying the foam insulator on top of your roof, you spray it on the underside of the sheathing.

This can be more tedious, especially if there are other structures, such as ceilings that are underneath your roof. You would need to tear those down for the insulation to be applied. 

Inner closed-cell foam and blown-in fiberglass or cellulose insulation

This internal closed-cell foam insulation is also similar to the previously mentioned insulation. Only this time, you would need to spray a layer of either blown-in fiberglass or cellulose insulation before applying the closed-cell foam. This is also similar to rigid outer foam combined with interior insulation.

Interior vs. Exterior roof insulation

As you have noticed, there are just two choices when choosing insulation, interior, and exterior. As we have mentioned above, some of their differences might get you thinking, which one better suits you? 

Both insulation systems have their own advantages and disadvantages, but when it comes to performance, interior insulation usually works better compared to exterior. This is because it traps and blocks heat and cold better, especially if properly installed. It also combats moisture better because of this. 

A downside of this is the cost. For exterior insulation, you only need to put it on your roof. For the interior, you might need to take down some structures like your ceiling to install them. The same is true with other insulations, like wall insulation.

Choosing which is which comes down to what you think will be more efficient for your situation. Even the design of your house or building can also play a part in choosing between the two. 

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