Loft & Attic Insulation

Over the last few months, you've undoubtedly heard about the present energy crisis. With energy bills constantly on the climb, it's more crucial than ever to insulate. Given that homeowners lose up to 25% of the heat in their homes through their roofs, warm loft insulation should be one of your first considerations when insulating. Browse our range of loft insulation rolls and PIR insulation boards to improve your thermal envelope and avoid winter catastrophe. 

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What Is Loft Insulation?


Loft insulation – sometimes referred to as attic insulation – is a barrier of insulation material designed to trap heat between rafters and joists in lofts. 

The most apparent advantage of an insulated loft is the reduction in energy bills. According to estimates, a quarter of all heat loss from a structure goes through its roof. If you could just manage to retain that heat in some way, your energy costs could drop by 25%. 

And this is where loft insulation comes in. Let's explore a few types of standard loft insulation below.

Loft Insulation Best Types

If you want to warm up your roof space, you first need to consider which insulating material is best for your project. 

You can either cut rigid insulation boards to size, utilise loft insulation rolls or have foam insulation sprayed between the rafters. Keep in mind that none of these are DIY jobs and will require a professional insulation specialist.

Loft Roll Insulation

Thermal efficiency lies at the heart of loft insulation rolls' many benefits. Loft insulation rolls boast a thermal conductivity of 0.044 W/mK, making them the perfect energy-saving companion.

As hinted by its name, glass wool insulation (fibreglass/blanket insulation) is made of spun glass fibres that are meshed together to form a blanket dense with air pockets.

It is these small pockets that trap gas (a poor conductor of thermal energy), ensuring heat is 'packaged' and retained within the fibrous matting of the insulation.

Most loft rolls come pre-cut or “combi-cut”. All the rolls in the Knauf Earthwool Loft Roll 44 range have perforations at 570mm and 380mm centres which means that they can easily be split to fit between standard joist and rafter spacings.

PIR Insulation Boards

PIR insulation board is a rigid insulation board comprising two high-performance aluminium facings sandwiched between a rigid PIR insulation core.

PIR (a widely-used shorthand term for 'polyisocyanurate') is equipped with a few simple properties that make it an excellent choice for a range of insulation needs; it has a closed-cell structure (and is water-resistant thanks to this), is extremely lightweight, and better yet, extremely thermally efficient.

With a thermal conductivity value of 0.022 W/mK, PIR is up there with the best insulators on the market, falling second only to phenolic insulation

PIR loft insulation board comes in a range of thicknesses from 20mm to 150mm and is perfect for pitched roof insulation. Its additional facings also provide extra protection against the elements - an added bonus for people who live in high rainfall areas.

Loft Insulation Between Rafters & Joists

PIR boards are the go-to choice for people who want to install loft insulation between rafters ( the beams that support your roof). 

Loft insulation rolls are the most common choice for loft joists (the horizontal beams across the floor of your attic). If you measure the space between them you can choose an exact fit. We stock a range of ready-cut and perforated rolls that you can simply roll into joist space.

Loft Insulation Over Boards

Many homeowners install loft boards so that their loft floor can withstand low-level foot traffic and light storage.

Most loft boards are made from chipboard, which is a rigid and moisture-resistant sheet material. These panels feature tongues and grooves, meaning they can slot seamlessly together for an easy installation process.

For optimum energy efficiency, we recommend installing insulation over the boards and installing another layer of boards on top. 

You must take the proper precautions to ensure that your insulation does not flatten when creating storage space; if your insulation is compressed too much by the weight of the boards it will become less efficient. You can use products like loft legs to ensure your insulation retains its shape.

Frequently Asked Loft Insulation Questions

Is Loft Insulation Flammable?

Loft insulation rolls feature excellent fire-resistant properties. Fibreglass insulation is naturally fire resistant, meaning that rolls made from glass mineral wool like Knauf Earthwool 44 Rolls have an A1 rating on the Euroclass scale. This A1 rating essentially means that they are anti-flammable and non-combustible.

PIR loft insulation boards, on the other hand, are not non-combustible. Celotex XR4120 PIR boards have a fire rating of E, whereas Recticel Eurothane GP PIR boards have a fire rating of F. You can use a build-up of other products to improve the overall performance of your materials against fire.

Is Loft Insulation Waterproof?

If you live in an area with high rainfall, PIR attic insulation boards are your best bet when insulating your loft. PIR has a closed-cell structure, which makes it resistant to moisture. 

Homeowners and commercial site managers can ensure the integrity of their spaces for years to come by investing in PIR insulation core boards. 

For added protection, you can install waterproof sheets over boards and between rafters to ensure the insulation maintains its thermal performance. 

Despite being exposed, glass mineral wool is hydrophobic, meaning it does not absorb water. You do not have to worry about mildew when you choose glass wool insulation. Like PIR boards, glass mineral wool insulation rolls work the best when they are protected with waterproof layers.

Which Loft Insulation is Best?

This really depends on what you are trying to achieve with your loft insulation. Most people install loft insulation to improve the thermal envelope of their building and reduce heat loss.

Using PIR rigid insulation boards at rafter level and loft insulation rolls at joist level is a very popular method for insulating a loft and will definitely improve the heat retention of the space.

If you want to go above and beyond to insulate your loft, you can use an insulated plasterboard such as Celotex PL board to add an extra layer of thermal protection to the attic space. This product can be mechanically fixed to the underside of the rafters, leaving a smooth plasterboard finish facing into the loft, and adding an extra layer of insulation at rafter level.

What is the Cost of Loft Insulation?

Unless you’re a multi-millionaire, cost is always an important factor when assessing any building project, and installing loft insulation is no exception. When weighing up loft insulation cost, it is also important to consider the long-term benefits of properly insulation your loft space, and what this might save in future heating bills. While paying a bit more for your attic insulation means a higher up front cost, you are likely to get this back over the coming years as you will have a more thermally efficient building.

While loft insulation rolls are the cheapest form of loft insulation, they are also the least thermally efficient, with a thermal conductivity of just 0.044 W/mK. Therefore if you decide to install loft roll between the joists in your attic, it is important to balance this by using a more thermally efficient product – such as PIR insulation board – in the roof.

While cost is an important factor, you should always weigh up the long-term benefits before deciding to prioritise price over quality. We have some of the cheapest prices on attic insulation of any online supplier. However, cheap doesn’t mean low quality – with industry-leading brands such as Knauf Insulation and Celotex – you’re sure to find effective loft insulation that won’t break the bank.

What Is The Difference Between Cold/Warm Deck Flat Roof Insulation?

A cold or warm roof application determines where you apply the roof insulation boards.