How to Insulate a Garage

Insulation, Membranes & Felts
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How to Insulate a Garage

As the UK property market is so uncertain right now, many homeowners are choosing to improve their current property rather than move on. This means there’s never been a better time to start work on your own home, for example refurbishing or converting your garage. Whether you’re looking to expand the amount of living space you have, or you need a dedicated home office, insulation is key to making your garage comfortable all year round.

How to Insulate a Garage: The First Steps

The first order of business is to take a step back and ensure your garage is ready to be insulated. This means giving it a good spring clean and making sure you’ve got open and easy access to the walls, roof, floors, and doors. Whilst you’re brushing away the cobwebs, this is a good opportunity for you to check for signs of damp or other problems that may need to be addressed before work begins.

Once your garage is sparkling and any damp or other issues have been resolved, you should then check the fit of the windows and doors. If either of these is letting in a draft, replacing them with insulated doors and double-glazed windows is advisable. This is especially important if your garage is going to become an office or a new living space for your family.

Following on from this, you should check the condition of your garage roof. This is particularly important for garages with flat roofs (as most are), as these are by far the most susceptible to issues such as nightmare leaks. Once you’re certain that your roof is fully waterproof, you’re nearly ready to get started. This process might be tedious, but it could save you untold amounts of time, money, and frustration in future.

You should also take this time to familiarise yourself with UK Building Regulations, as extensive refurbishment work on properties normally require a raise in overall insulation performance. You should typically be aiming for the below targets, but it is always worth double checking the national and local regulations before getting started to ensure you permission for your build and understand what is required from it.


Flat Roof




0.18 W/m2K

0.28 W/m2K

0.22 W/m2K


0.13 W/m2K

0.17 W/m2K

0.15 W/m2K


0.15 W/m2K

0.21 W/m2K

0.18 W/m2K

Determining the thickness of insulation you’ll need to meet the above requirements can be tricky, but thankfully there are plenty of free U-value calculators available online.

Now you’re all prepped and ready to insulate your garage.

How to Insulate Garage Walls

The majority of garages in the UK have walls that are made up of just a “single skin” of breeze blocks. For these, you have a number of insulation options to choose from, which we’ll speak more about below. Some British homeowners may find that they have what is known as a “double skin garage”, which means its breeze blocks are surrounded by brick walls with a cavity. As these garage walls will likely require blown-in insulation, this is not something that should be attempted by a DIYer.

However, if the condition of your garage’s walls is dissatisfactory, there is the option of deconstructing them, insulating the walls, and then rebuilding the wall. This is of course expensive and potentially troublesome, so only attempt to do so if necessary and you feel confident to undertake the job.

Internal Wall Insulation

You have a few options to choose from when insulating internal garage walls. The most tried and tested method is to construct a timber frame against the inside of the walls and install insulation slabs in between the sections of the timber frame. If you’d like to add another layer of protection, you could also install a full multifoil insulation system over the slabs, which will make the space more comfortable and improve internal air quality.

External Wall Insulation

If your property features a detached garage, it may be wiser to opt for external wall insulation. This will involve fitting insulation boards and suitable render systems to the external walls. Increasing the thickness of the outside of your garage may seem odd, but the internal space savings could be well worth it.

How to Insulate a Garage Roof

Choosing the right garage roof insulation for your property will largely depend on whether your garage has a pitched or a flat roof. Garages with pitched roofs can be insulated in much the same way as when fitting loft insulation in your home. High-quality PIR insulation boards in conjunction with a multifoil system will protect your garage from mould and damp, as well as make it a far more comfortable living space. What’s more, these products are quick and easy to install, with no need for specialist tools.

When it comes to garages with flat roofs, you have the choice between constructing a warm roof or a cold roof:

Warm Roof

Warm roof construction refers to flat roofs where the insulation materials are fitted above the roof deck. This option is generally the most recommended route to go down, as it maximises internal space by retaining your full ceiling-to-floor height, whilst keeping your roof deck warm and reducing the risk of condensation build-up. Before constructing a warm roof, you should ensure that your roof deck is free from damage. You may need to install a vapour control layer if your roof deck is not fully water-tight.

Cold Roof

Cold roof construction is the name for flat roofs where the insulation layer is below the roof deck. They’re referred to as “cold roofs” because any area above the insulation (i.e. the roof deck, loft, or roof space) will be colder than the living space below. This can present a problem as colder areas are more susceptible to condensation. If you’re opting for a cold roof, we’d suggest first screwing 50x50mm battens to the side of your rafters below the roof deck. This will ensure that you maintain an air gap of 50mm. A void should also be left behind the fascia, to ensure the free flow of air throughout.

How to Insulate a Garage Floor

Uninsulated garage floors can become incredibly cold, so underfloor insulation is a must if you want your garage to be a viable living space during the winter months. We supply a range of excellent floor insulation boards for you to choose from, including the Celotex GA4000. This PIR board is perfect for achieving that warm, welcoming feeling thanks to its fantastic performance, and its thin design ensures you’ll lose minimal space.

Once you’ve chosen the right garage floor insulation for your project, there are a few more things to consider. If you’d like to retain the concrete slab floor of your garage, you should install a damp-proof membrane before any insulation. Depending on the level of your garage floor in relation to the rest of your home, it may also be necessary to consider adding a step up between the rooms.

How to Insulate a Garage Door

Now that the bulk of your work has been completed, insulating your garage door is the final step. While this is optional, you’d be amazed at the difference insulating the door can make to an otherwise cold metal surface. We’d recommend installing a layer of SuperFOIL SFBA insulation fixed by foil tape. If your garage door section is particularly deep, insulation rolls such as Knauf’s Earthwool could be considered. Be mindful however of the thickness of your chosen insulation, particularly if your garage door is an “up-and-over” style.

Final Considerations

As mentioned before, the range of insulation available to you can seem staggering, with dozens of factors to compare between each. There are so many things to consider, but it’s important to choose the garage insulation that’s right for you. If your garage is going to become a workshop, then acoustic insulation may help dampen the noise from power tools. If your garage is going to become a nursery, then safety will naturally be your top priority.

Whatever your plans are, making the right choice is vital. If you’re still unsure, then get in touch with our award-winning customer service team. They’ll be able to talk you through the pros and cons of each option, and advise you which insulation is best for your needs. Call them on 01295 565 565, email [email protected] or use our handy live chat.

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