In the UK, there are 21 million homes with poor insulation: this means poor energy efficiency and higher energy bills.
For flat roofs, insulation is especially important, as the roof structure can prevent unique challenges. But, good insulation installed correctly will help to maintain the temperature inside, reduce the amount of energy you use, and prevent any buildup of moisture.
In this blog, we’re going to take you through what insulation is, insulation options, if they are energy efficient, and what is the best choice for you.
What is Flat Roof Insulation?
Insulation adds a thermal barrier to the flat roof to keep the inside of your home warm in the winter and cooler in the summer.
Thermal insulation traps heat during the winter, reducing the amount of heat you lose, and reflects sunlight in the summer, keeping your house cooler. Overall, installing insulation will reduce your energy consumption, bill, and reduce your carbon footprint.
Acoustic insulation materials reduce noise pollution, so they are a great choice if you live in a built-up area!
Cold Roof Vs Warm Roof Insulation
Choosing between cold flat roof insulation and warm flat roof insulation not only affects energy efficiency but also ensures your roof meets UK building regulations for thermal performance and U-values.
Cold Roof
A Cold Roof means the insulation materials have been installed on ceiling joists, rather than directly under your flat roof deck. The insulation is placed over and between the ceiling joists, meaning there is still room for using the loft space for storage.
The benefits of a cold roof loft insulation include: it is easy to install, and fewer materials and labour are needed, so it is not only easy, but the cheaper and more cost-effective method.
However, there is a higher risk of condensation that comes with this type of insulation, as well as having a lower thermal efficiency rate. It’s also not ideal if you use your loft roof space for anything other than storage.
Warm Roof
For a warm roof, insulation materials are installed about the structural deck and below the waterproof layer (membrane). This creates a continuous thermal barrier across the whole of the flat roof structure. With this insulation, it stays warm in the winter and cool in the summer.
If you’re using your loft as a living space, it may be the better option for you.
This technique is the best way to insulate your flat roof, as it has a much better thermal performance. It prevents moisture and removes the need for ventilation. Overall, this helps to extend the lifespan of your flat roof. It is more complex to install and cannot be installed on an existing flat roof, meaning it is usually the more expensive option.
Types of Flat Roof Insulation
To improve the thermal performance, it’s essential to choose the correct flat roof insulation. Different materials offer varying levels of energy efficiency and resistance to moisture.
Rigid Board Insulation
Rigid insulation boards are one of the more popular solutions for modern flat roof systems. They are made from Polyisocyanurate (PIR) and installed above the roof deck in warm roof setups.
This type of insulation provides good thermal performance, characterised by low thermal conductivity values. This means you need less thickness to achieve a lower U-value. (This measures how effectively it insulates by showing the rate of heat loss through the entire structure.) It is also well known for its fire resistance and strength.
- Lightweight and easy to handle
- High compressive strength for flat roofs
- Excellent energy savings due to low heat transfer
Mineral Wool Insulation
Mineral wool (also known as rock wool or stone wool) is a dense fibrous insulation material manufactured from natural rock or recycled slag. It is typically used in flat roofs where enhanced fire performance is required or where sound insulation is important.
Though slightly less efficient than PIR boards on a thickness basis, it has a density that reduces heat loss whilst also offering acoustic absorption. It is suitable for both cold and warm roof setups, but it is challenging to install.
- Superior fire resistance (non-combustible)
- Great for flat roofs on commercial or high-risk buildings
- Provides both thermal and acoustic insulation
Expanded Polystyrene (EPS)
EPS (Expanded Polystyrene) is a foam-based insulation material commonly used in inverted roof systems.
It offers good thermal properties and is widely regarded as a cost-effective method of insulating flat roofs.
- Affordable insulation solutions
- Lightweight and easy to install
- XPS is ideal for roofs with higher moisture exposure
Spray Foam Insulation
Spray foam insulation is applied as a liquid and expands to form an airtight, seamless layer. It can be applied to the underside of the roof deck, although it must be installed correctly by trained professionals.
Because it eliminates gaps and reduces air leakage, spray foam offers excellent thermal efficiency. Its ability to create a continuous insulation barrier helps reduce heat loss and improve airtightness.
- Great for irregular or difficult-to-reach areas
Reduces thermal bridging - Creates an airtight seal, improving heating efficiency
Choosing Roof Insulation for You
When it comes to finally choosing your installation, it’s best to consult an expert, like a member of the Western Flat Roofing team, and talk about what you want.
You will need a moisture-resistant material to reduce pooling on any flat roof, and you should look at the U-value and the R-value. For U-Value, lower is better, and for R-Value, higher is better.
Budget also plays a big factor; there are cheaper and more cost-effective options, but these don’t tend to perform as well and can cost you more money in the long run.
