Insulation on roofs is one of the best way to cool or to heat a house or a building without the need to expend electricity. It helps reduce power consumption and in return lower electric bills. In this article, we have researched and asked the experts multiple ways on how to insulate an existing flat roof. This is what we found out.
Insulating an existing flat roof could require major renovation depending on type. You might need to take down and replace existing structures of your roofing system. This would prompt you to hire a contractor in most cases, especially if the size of your roof is large. Below are some ways to insulate an existing flat roof.
- Outer rigid foam insulation
- Outer rigid foam combined with interior insulation
- Outer closed cell-foam insulation
- Inner closed cell-foam insulation
- Inner closed-cell foam and blown-in fiberglass or cellulose insulation
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!
Some ways to insulate a 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.
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.
How do you deflect heat from a flat roof?
Insulating your roof is the number one option when it comes to deflecting heat off your flat roof. Deflecting heat off this type of roofing has been along practice, especially that this roofing is common in countries with arid climates.
Aside from the insulations mentioned earlier, here are some intuitive actions that you can do deflect heat off of your flat roof.
Shading
Never underestimate a good shade when it comes to deflecting heat off flat roofs. And since flat roofs are usually accessible and are designed to be a living space, putting a shade such as a tarp or any form of extra object, that would serve as another roof on top of your flat roof.
This will serve as the first line of defense against the heat and will be the one recieving the brunt from the scorching sun. This will also be ideal if you are planning to spend time on your flat roof even if it is a sunny day.
Graveling your roof
Placing gravel on top of your flat roof is another great way in deflecting heat off your flat roof. You can add gravel as the flooring of your flat roof as this is effective and will help in reducing the temperature below your roof.
With this opens other designs that goes with a gravel floor you can do with your flat roof, so be creative with it. This makes gravel not only an insulator but also an aesthetic feature for your house.
Other forms of insulation
Other forms of insulation is by adding a green roof or a living roof on your flat roof. This is basically a garden on top of your flat roof. By putting some type of vegetation on your roof, this greatly reduces heat from being absorbed. And with plants, this also serves as an additional shade for the roof. Just make sure that the integrity of your flat roof is sturdy as the weight of a loam soil is heavy.
What is the best material for covering a flat roof?
Coverings on your flat roof is another way of adding insulation and deflecting heat. Earlier, we have discussed gravel as a great option for heat deflection, it is also a great flat roof cover. Below are some other types of flat roof covering that you can choose.
Rubber
Rubber coverings are also known as an EPDM covering or an Ethylene Propylene Diene Monomer cover. It is a new innovation when it comes to flat roof covers.
It is made out of synthetic rubbers [butyl], which is the same materials used for inner tubes of clincher tires. This type of flat roof covering works well against the elements and against the harmful UV rays of the sun.
Modified Bitumen
Modified Bitumen is an upgrade from tar or gravel coverings. It is made out of membrane comprised of multiple layers from polymer-modified butimen. This covering is applied by heating the bottom part of the fabric cover and then it is rolled on.
PVC or Vinyl
A PVC or vinyl flat roof covering are apllied at the seams after being heat-welded. This makes it very durable against weathering. It also adds pliability to the cover making it impervious to heat.
If you have aspahalt on your flat roof, a separator sheet mjst first be installed as both are incompatible. This is due to asphalt having the tendency eating through the covering.
Can you insulate between joists on a flat roof?
Yes, you can insulate between joists on flat roofs, this is what we call a cold flat roof. It is when the insulations are installed between roof joists including above your vapor control layers and plasterboards. While an insulation put on top of your roof is calles a warm flat roof.
Other common insulating methods are either under or over the joists. Below and between joists insulations on the other hands are the prefered method if you are re-roofing or renovating your structure. All insulations work fantastically for your building.
A short recap
There are a plethora of ways to insulate your flat roofs. From interior to exterior insualtion, covering like PVC and vinyl, modified bitumen, and rubber. To gravel and even creating a garden on your falt roof, these all help in creating insulation for your roof, especially to combat against the heat.
Choosing between interior or exterior insulation will depend on your preference and even the design of your house. In most cases, interior insualtion woiuld be more expensive but it is the more superior insulation.
Below are some of our previously written articles just for you, so go ahead and check them out to learn a thing or two!
Best Insulation For Ceiling Under Roof
How Many Roof Vents Do I Need?
Does A Warm Roof Need Ventilation?