How To Insulate A Loft Conversion

If you're considering a loft conversion for your home, you will soon find that there is a huge range of things that you need to consider. Near the top of the list will be insulation. For your loft insulation to meet building regulations, it will need the right level of insulation. Decent insulation will also help to lower your energy bills and make your loft conversion a more comfortable place to be.

Insulate A Loft Conversion

What Do Building Regulations Say About Loft Insulation?

A loft conversion is subject to quite strict building regulations. These regulations will cover a wide range of aspects, including staircase installation, fire safety measures, and electricals. But they also cover loft conversion insulation.

Building regulations for loft conversions dictate that the insulation must reach a high enough level. The insulation level is measured with a U value. This is the rate of transfer of heat through a structure divided by the difference in temperature across that structure. The unit this is measured in is W/m2k. The lower the value, the better the insulation.

Where there is currently no loft insulation, any installed insulation in a loft conversion will need to reach 0.16 W/m2k or lower. Where there is currently loft insulation but it is at 0.35 W/m2k or higher, you will need to improve the insulation so that it reaches 0.16 W/m2k. This is known as retrofit loft insulation and it can greatly improve the energy efficiency of a property.

Cold Roof Vs Warm Roof

When looking into loft insulation, you will come across the terms "cold roof or cold loft" and "warm roof or warm loft". These terms refer to different approaches to insulating the roof space of a property. For the house below, having a cold roof or a warm roof won't make much of a difference. But where these approaches can have an impact is on the loft space itself.

Cold Roofs/Cold Lofts

Simply, cold roof insulation provides thermal insulation for the living spaces in the home but leaves the loft space subject to temperature fluctuations.

The insulation is installed only on the floor of the loft. So everything from the ceiling below the loft downwards is kept warmer because the heat is slower to escape into the loft. But because the roof isn't insulated, there is rapid heat loss from the loft to the outside. This can make it feel cold.

This type of loft insulation is not suitable for a loft conversion that aims to create a comfortable living space, bedroom, games room, office, etc.

cold roof insulation

Warm Roofs/Warm Lofts

Warm roof insulation provides thermal insulation for the entire building from the roof downwards.

The insulation is installed in the loft walls and floor. This means that heat loss is slowed down throughout the property, including the loft. And so the loft is kept warmer.

Because the loft is kept warm, it can be used as a living space.

Gain insights: How Much Value Does A Loft Conversion Add

Warm roof insulation

Insulation Material Options For Loft Conversions

There are a lot of options to choose from when installing insulation in a loft conversion. The material type itself can vary so much because lots of different materials can work well as an insulator.

What Is Insulation?

All types of insulation materials work by slowing down heat loss. This can be achieved in three different ways:

  • Conduction - heat is lost when it is transferred between molecules in a solid substance. Many insulating materials have a small mass, which reduces conduction
  • Convection - heat is lost when it is transferred in a liquid or a gas. Many insulating materials have air pockets, which trap the heat and reduce convection
  • Radiation - heat is lost through electromagnetic radiation. Many insulating materials have enough mass that they can block radiation


The best insulating materials will reduce conduction, convection, and radiation. Importantly for loft conversions, however, some types of materials will only be able to reach the necessary U-value by increasing their thickness by quite a lot.

This can be a problem when insulation is installed in a loft floor or roof covering. One major challenge when converting a loft into a usable living space is the amount of headspace you are left with. Lofts were not originally built with the potential use as a living space in mind.

Often, there isn't much height to work with, especially when there is a sloping roof. There should be a minimum of 2.2 metres, and ideally 2.4 - 2.5 metres, between the top of the floor joists and the bottom of the ridge timber. Once the insulation has been installed, this should leave you with around 2 metres of headroom.

If the insulation can only meet the minimum U-value by greatly increasing its thickness, then this will cut into the amount of headroom you have available and could make the loft conversion more challenging to use comfortably.

For example, insulation rolls or batts will need a minimum thickness of 270mm but if you are using an insulated plasterboard, then you can achieve the same U-value with just 150mm of thickness.

The U-value doesn't just take into account the insulation itself. It measures the thermal insulation of the entire material that surrounds your loft. So it will also include:

  • Roof tiles
  • Stud walls
  • Breathable membrane
  • Wooden rafters
  • Plasterboard
  • Finished plaster skim
  • Paint

This is partly why insulated plasterboard can achieve a better U-value with less thickness.

Loose-Fill Insulation

Loose fill insulation is an inexpensive but effective material for insulating a loft conversion. It comprises small, loose pieces of insulating material. This could be cork granules, mineral wool, recycled newspaper, or cellulose fibre.

These lightweight granules are poured directly between joists to fill them to the required depth of 270mm.

Loose-fill insulation is a good option for hard-to-reach areas such as below a pitched roof or above gabled dormers and it can be used on its own or as a top-up to existing insulation.

Loose Fill Insulation

Blanket Insulation

This is one of the most popular options to insulate a loft conversion. It is made from batts or rolls of wool insulation and this can either be synthetic mineral wool or genuine sheep's wool. This type of insulation is perfect for a flat roof, loft floors, and roofing timbers.

If you are using rolls, the pieces can be cut to size and then placed within the joists of the loft floor space or roof room ceiling. If you are using batts, these will be pre-cut into rectangular pieces that can then be placed. Laying wool insulation in rolls allows you to cut irregular pieces that can be used in spaces that will otherwise be difficult to reach.

To reach the recommended depth of 270mm, blanket insulation will sometimes end up higher than the height of the joists. In this situation, you would need to use loft legs to lift the floor.

blanket insulation loft

Insulating Board

These are firm boards that are full of either synthetic or natural materials. They are the best solution for insulating the underside of a sloping roof roof and they can be used for walls and floors as well.

They are inflexible and will break if you try to cut them so you may need to use other insulating materials to plug up any gaps and prevent thermal bridging.

Foam board is one of the more expensive insulation options but it can be worth it. The boards don't need to be 270mm thick to reach the required U-value and can instead be as thin as 150mm. This will leave you with a lot more residual loft space that can be converted into a usable room.

You can also get aluminium-backed insulation boards that will increase the radiant insulation. So for very little insulation thickness, you can achieve a high level of insulation that will keep your house warmer and reduce your energy bills.

Insulating Board loft

High-Performance Spray Foam Insulation

High-performance spray foam insulation can either be an open or closed cell. Closed cells are denser and more rigid but provide better thermal performance and moisture resistance.

Open-cell spray foam expands much more than closed cells can be used for harder-to-reach areas and can provide additional soundproofing.

Spray foam insulation can be more expensive than other options and it has to be installed by a professional. It is also difficult to remove once it has been installed.

High Performance Spray Foam Insulation

Benefits Of Loft Insulation

If you are having your loft converted, then now is a good time to really think about insulation. Insulating your home has a wide range of benefits.

Benefits Of Loft Insulation

Reducing Heat Loss

A lot of the heat you lose from your home is through the roof. Heat rises and if there isn't sufficient insulation in a standard loft, then a lot of heat will be lost. This will leave the rest of your home feeling colder.

Reducing Heating Bills

Because more heat is being lost, you will need to use more energy to heat your home. Improving the insulation in your loft will mean that you need to use less energy for heating so your heating bills will get lower.

Being More Environmentally Conscious

Reducing your energy usage will mean that your carbon footprint is lower and you are doing more to help the environment.


This is especially important if you are converting your loft to an extra living space. Extra insulation will reduce the noise pollution from outside, making the room (and the rest of the house) more comfortable to be in.

Increasing Property Value

Improving your insulation will give you a higher EPC rating. This is the Energy Performance Certificate and it scores your home on how energy efficient it is and how much energy it uses. The better insulated your home is, the better EPC rating you will get. A higher EPC rating can increase your property's value because it makes it more of an attractive option for buyers.

Can I Insulate My Loft Myself?

If your roof rooms are just going to be residual space, then it is entirely possible to insulate a loft yourself. If, however, you are planning to convert your loft to a habitable room, then you will usually need a professional.

A loft conversion will need to get building regulations approval to be classed as an extra living space and the insulation levels, including the U-value, are an important element that will be considered.

Lofts can be complicated to insulate. Dealing with sloping roofs or a sloping ceiling can make installing insulation more difficult, as can the spaces between joists and other roofing elements. Avoiding thermal bridging (cold spots in the gaps between insulating materials where heat can be lost) when insulating a loft can be difficult without the help of a professional.

Can I Insulate My Loft Myself

How The Loft Crew Can Help With Your Loft Conversion Insulation

We have decades of experience in constructing high-quality loft conversions. And we understand the importance of insulating a loft conversion. We will ensure that your new loft conversion is insulated to building regulations standards or beyond. Retaining as much space in the roof room as possible is also a key consideration and this will be part of the design and material choice when we insulate a loft conversion.

Our team of experienced and knowledgeable contractors will ensure that the insulating material is installed correctly and that it gives you the level of insulation you require, without compromising too much on space.

Dig deeper: How Do You Know If You Can Have A Loft Conversion

Final Thoughts

There are a range of options for insulating a loft conversion. Building regulations dictate that a loft conversion should have a certain level of insulation for it to get approval but this can be achieved using various methods and materials.

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