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Flat Roof Insulation Systems

Flat Roof Insulation Systems

Flat Roof Insulation Systems

When it comes to flat roof insulation systems, there are wrong ways, and right ways to insulate them. The first questions that come to mind when people think of insulating a flat roof is where, and how.

The answers to these questions are very important. Especially when your flat roof is located in a room that generates high levels of humidity, such as the bathroom.

There are many ways to insulate a flat roof, or a low-slope roof. The problem is, most of them are wrong.

Some of the usual methods include fiberglass or cellulose on top of the leaky ceiling. People leave a gap of a few inches between the top of the insulation and the roof sheathing. And while this system will work in most cases, there are much better options.

Let’s look at your flat roof insulation systems options, as well as why you should start such a project in the first place…

Why Insulate A Flat Roof?

Flat roofs are usually found in bathrooms and other type of extensions. They are not the best of ideas. Flat roofs lose heat, they are prone to leaking, and most importantly of all, they cause the materials to deteriorate over time.

Many houses suffer from the same problem. When you think of insulating a flat roof, it is better to replace the roof covering instead. Your second most important task is to understand how to keep it airtight and prevent condensation.

Types Of Flat Roof

Depending on the roof type your property possesses, you need to consider how to insulate, where to insulate, and the thickness required. Let’s look at the two main types of flat roof:

Cold Flat Roof

Most of the traditional flat roofs belong in the “cold roof” construction category. Cold roofs usually have a vapour control layer in the ceiling, and cross ventilation at the eaves, or sometimes on the top of the walls.

These features help with condensation. However, this roof type encourages heat loss; so much so that the system was banned in Scotland.

Warm Flat Roof

In this case, the insulation can be placed below the weather proof membrane. The construction is called “warm roof deck construction”.

You can also place insulation above the waterproof membrane, which is referred to as the “inverted warm deck”.

Flat Roof Insulation Systems

Why A Vapour Control Layer Is Crucial

The vapour control layer always goes above the deck. This layer is put on the warm side of the insulation, and takes the form of reinforced bitumen sheeting. Sometimes, companies opt for a polyethylene laminated vapour layer, with metal foil that reflects heat.

The vapour control layer is essential for both ventilated and unventilated roofs. On a side note, all flat roofs are unventilated. A vapour control layer serves the purpose of protecting thermal insulation from potential points of entry for moisture.

For example, the layer protects against leaks, damp building materials and similar.

You can use a vapour control layer with all types of insulation, as long as they are fibrous and organic insulating materials.

Insulation Thickness Advice

Depending on which type of insulation you use, the thickness can vary. The chosen insulation should be able to withstand the weight of anything positioned above it on the roof.

The typical U-value of an uninsulated flat roof is 1.5W/m2k. Your target is to achieve a U-value of 0.25W/m2k, or better.

Here is how much insulation you need depending on the material:

– With fiberglass insulation, 300mm of thickness results in a U-value of 0.22W/m2k, while 500mm of thickness results in 0.15 U-value

– With mineral wool slab, 150mm of thickness gets you to a U-value of 0.22, while 250mm gets you to 0.15 U-value

– Polyurethane insulation of 100mm gives you a U-value of 0.22, while thickness of 150mm gets you to 0.16 U-value

As you can see, the best flat roof insulation system is polyurethane, more commonly known as spray foam insulation.

spray foam insulation near me Flat Roof Insulation Systems

Problems With Flat Roofs 

We explored why you need to insulate a flat roof and which flat roof insulation options you have available to you, but let’s delve deeper into the problem itself. First off, what is a flat, or a low-slope roof?

Simply put, it is a roof that is flat or almost flat. This type of roof is often found in urban areas. Some of the roofs have parapets on just one side of the roof, others have on three or four.

As long as the job is done correctly, insulating a flat roof the traditional way is great. That means insulating with an airtight ceiling, and adequate attic ventilation.

The problem is, most of these walls are not constructed correctly. The result is that air leaks out through the ceiling, and the attic ventilation is poor and inadequate.

Ventilation pulls warm and moist interior air through the cracks. Once the air is in the tiny attic, you get moisture accumulation in the cold roof sheathing, and eventually mould and rot.

Architects simply do not want to provide any ventilation around the perimeter. Sometimes, architects do not provide deep enough truss to get insulation.

That being said, we talked about types of flat roof insulation systems. What is your best option? As we saw previously, polyurethane spray foam offers the best R-value. But what are some other benefits of spray foam?

How Spray Foam Can Solve Them

There are many benefits of spray foam insulation that will make you consider it. Whether your building is old or new, spray foam is arguably the best flat roof insulation systems option on the market.

Yes, the initial investment is greater than other types of insulation. However, in the long run, spray foam is the most cost-effective product available, and saves money on your energy bills starting from year 3.

One of the unique abilities of spray foam is to penetrate and fill small cracks and crevices. No other insulation material provides such superior sealing. Applying foam into the cracks allows the foam to expand, preventing air leakage in the process. 

Spray foam also helps with noise reduction. If your neighbours are party animals, noise pollution is pretty much par for the course.

Yet by installing soundproofing foam in your home, peace and quiet will finally be restored. Bliss!

Spray foam also prevents pollen and other allergens from entering the building. Because it reaches all of the cracks in your walls and roof, spray foam prevents air from penetrating the walls. 

Speaking of allergens, we also have to mention bugs, insects, and small rodents. Spray foam prevents all of the aforementioned critters from sneaking into your humble abode, by sealing the tiny holes in the structure of your building.

Open and closed cell spray foam insulation also curb condensation considerably.

We mentioned that spray foam’s initial cost is higher than other types of insulation. However, spray foam reduces energy bills by up to 50%. And it lasts longer.

Once installed, spray foam performs for the life of your building. Unlike cellulose, spray foam does not sag or shrink over an extended period of time.

Last, but not least, spray foam is an eco-friendly material. If you are concerned with keeping your house “green”, spray foam is the way to go. Reducing energy consumption is just one aspect how spray foam is eco-friendly.

We hope we have answered any questions you have in regards to flat roof insulation systems. Ready to revamp your flat roof into an energy-efficient all-rounder? For more flat roof insulation know-how, simply click the button below!

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