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How to Insulate a Loft Conversion

Updated on:
April 30, 2024
How to Insulate a Loft Conversion

Image Source: Canva

A loft conversion can be a beneficial addition to many homes. They can be used as an extra storage area or a whole new living space, such as a bedroom or an office. A loft conversion can also increase the value of the property.

Insulating a loft conversion will help to reduce your energy bills and make your home more eco-friendly. There are quite strict regulations surrounding insulation and loft conversions, however, so it is important to get this aspect of them right. There are quite a few options out there for insulation placement and materials. Let's take a look.

What is a loft conversion?

When most homes were built, the attic space would be left empty. There might be some elements of the boiler system and there would be insulation material but otherwise, it would just be unused space.

Converting this loft space into a usable area can increase the square footage of the home. You might choose to use this for storage or as an extra usable room. Loft conversions can also increase the value of your home, typically adding an extra 10% - 20%.

Because of these benefits, there has been a rapid increase in loft conversion popularity in recent decades.

While all lofts will have some insulation, you will likely need to invest in new insulation when converting your loft.

This insulation can create even more benefits by reducing your energy bills. The slower the heat loss from your home, the less energy you will need to heat it, and the lower your heating bills will be.

What type of loft insulation do I need?

You may have heard the terms "cold roof" and "warm roof". There is an important distinction between these types of insulation that can affect the use of your loft conversion.

Warm loft insulation

A warm roof is when the loft space itself is insulated, as well as the building below. The loft insulation is installed in both the loft walls (or roof room ceiling) and the loft floor.

It is both between and above the rafters and most of the insulation is placed above the roof's timber. This also serves to reduce thermal bridging (spaces where there is no insulation and heat can be lost).

Cold roof insulation

A cold roof insulates only the building below the loft. The loft itself isn't insulated so it will remain cold. In this case, the insulation is only placed on the loft floor. There is none installed in the loft walls and no insulation at the rafter level. This is the conventional method for insulating a loft when there is no conversion.

If you want to use your loft conversion as a living space, you will need to install warm roof insulation. Cold roof insulation would leave the room unusable as a living area but would be fine for a loft space that is used for storage.

For a loft conversion that is a living space, the insulation must be covered and you will need to include acoustic dampening and fireproofing.

Building regulations for loft conversion insulation

There are tight rules and regulations surrounding loft conversion insulation. These are related to the thermal efficiency of the loft insulation.

The regulations for loft conversions dictate the U value that the insulation should hold. The U value is the rate of transference of heat divided by the difference in temperature across the structure and it is expressed as W/m2K. The lower the U value, the better the thermal insulation.

The regulations differ slightly between Wales, England, and Scotland and they can be fairly complicated.


The minimum U value for a refurbishment is 0.16 W/m2K. For an extension, it is 0.15 W/m2K.


The minimum U value for new builds is 0.1 W/m2K. For refurbishments, it is 0.15 W/m2K for a pitched roof at ceiling level and 0.18 W/m2K for a pitched roof at rafter level or for flat roofs. These values can change if the original U value before conversion is at 0.7 W/m2K or higher.


The minimum U value for a pitched roof insulated at rafter level is 0.18 W/m2K. For flat ceilings, it is 0.16 W/m2K. For a complete roof covering, the minimum U value is 0.15 W/m2K.

Image Source: Canva

What type of insulation material should I use?

There is a wide range of options for insulating materials that can be used in a loft conversion. All types of insulation work by slowing down the transfer of heat. Usually, insulating materials will have little mass but lots of air pockets. This reduces heat loss in three ways:

  • Conduction - this is where heat is transferred between molecules in a solid substance. The small mass of insulating materials reduces this.
  • Convection - this is where heat is transferred in gas or liquid. The air pockets in insulating materials reduce this because they trap the air molecules.
  • Radiation - this is when heat is lost through electromagnetic radiation in the air. Insulating materials have enough mass to block this radiation.

Most types of insulation will slow down heat loss through these methods but the different materials you choose can have their own benefits and limitations. You will also need to consider the width of the materials. Some of them require greater thickness to achieve the right level of insulation, which can reduce the headroom in the loft.

Blanket insulation

Blanket insulation is one of the most common types of loft insulation. It is usually made from mineral wool or sheep's wool. It comes in rolls or slabs and is cut to size and then fitted. It requires a thickness of around 270mm. Laying wool insulation is relatively quick and simple.

Loose-fill insulation

This type of insulation is usually made from lightweight materials such as cork, mineral, recycled newspaper, or cellulose fibres. These are in the form of small granules. They are poured between the joints to create the insulation. Loose-fill insulation can also be used to top up existing insulation to reduce thermal bridging.

Insulated plasterboard

Insulated plasterboard can be a good option for loft conversions because it can be easily cut to shape and can cover large areas easily. It is also quite thin for its thermal performance. The boards are rigid and made of gypsum or foamed polystyrene, polyiso, or polyurethane. They can be dry-lined after installation.

Spray foam insulation

Spray foam insulation is made of polyurethane foam (SPF) and is an alternative to traditional loft insulation. It comes in two forms: open cell and closed cell. Open cell spray foam insulation can expand to up to 100 times its original size, allowing it to reach hard-to-reach areas.

Closed-cell spray foam insulation is more rigid but can provide additional structural integrity and support to the building itself. This type of insulation is unique because it can be sprayed into every nook and cranny, reducing thermal bridging.

While spray foam insulation can be more expensive than traditional insulation materials, it is versatile, can be fitted to any shape and harder-to-reach areas, includes soundproofing capabilities, and reduces condensation.

Installing insulation

It is possible to insulate a loft yourself, depending on the type of insulating material you are using. Plasterboard and blanket insulation are both relatively easy to DIY install, in many cases. However, a professional can often ensure that the insulation is installed properly, to its required depth, and without any thermal bridging.

For spray foam insulation and loose fill, a professional is usually required. Loose-fill insulation is best installed with a blower machine to ensure that it has an even lay. Spray foam insulation also requires specialist equipment to install.

Final thoughts

Insulating a loft conversion is required according to building regulations. The areas of the loft that need to be insulated will depend on whether you are planning on using the loft as a living space or simply for storage. There are also several different insulating materials that can be used.

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