How to Insulate a Garden Room, Summerhouse or Shed

Garden room insulation is the key to transforming your garden room, summerhouse, or shed into a comfortable, year-round living space. Whether you’re creating a serene retreat, a productive home office, or a cosy guest room, proper insulation helps maintain a consistent temperature while reducing energy costs. Without effective insulation, these outdoor structures can become unbearably cold in winter and stiflingly hot in summer.

In this guide, we’ll walk you through the best insulation methods to maximise comfort, efficiency, and usability in your garden haven. For a comprehensive overview of planning and building your space, explore our detailed garden room construction guide.

If you are here specifically to learn how to insulate a garden room, check out my latest in-depth guide here:

Why Insulate a Shed, Summerhouse, or Garden Room?

Insulating your garden building turns it into a comfortable, year-round space you can enjoy in any season. Good insulation keeps your garden room warm in winter, cool in summer, and more energy efficient, helping to reduce heating and cooling costs.

It also adds soundproofing and protection against damp and mould, creating a quieter, drier, and healthier environment. Whether you’re building a garden office, hobby room, or relaxing retreat, insulation makes your space more practical and enjoyable.

What’s Included in This Free Guide

In this guide, you’ll find real examples of insulating a shed and a garden room log cabin, plus advice on insulating summerhouses with multiple windows. We cover the best insulation options, step-by-step installation methods, and cost-effective ways to insulate garden buildings.

Whether you’re creating a garden office or a cosy retreat, this guide shows you how to get the most from your outdoor space, and if you’d rather use a professional, companies like Your Choice Builders can design and build insulated garden rooms to your exact needs.

My garden room office (pictured above) was purchased from Garden Buildings Direct. It’s a prefabricated garden room (log cabin) with loads of potential for modification and insulation for year-round use.

For more detailed information about how I built and insulated this building, read more here:

The Key Benefits of an Insulated Garden Building

Insulating a garden building improves thermal efficiency, helping heat stay inside during winter and reducing heating costs. At the same time, insulation reflects external heat in summer, keeping your shed, summerhouse, or garden room cooler.

Heat loss in a garden building is similar to that of a house, with warmth escaping through the walls, floor, roof, and windows. Understanding where heat is lost helps you target insulation more effectively for maximum performance.

• 25% through the roof
• 35% through the walls
• 10% through the windows
• 15% through the doors
• 15% through the floor

Heat is lost in all directions, so it’s important to insulate every part of your garden building, especially the walls.

This guide covers three key topics: how to insulate a summerhouse, how to insulate a shed, and how to insulate a garden room. You’ll start with a general insulation method suitable for most garden buildings, followed by more specific guidance for each structure type.

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Insulating the roof and walls

You may be limited with the thickness of insulation you can use on your walls and roof. The slimmest insulation available can be as small as 3mm, but this isn’t going to be effective. If possible, use a 25 – 50mm insulation board or wool. I’ve used both before and either can be effective. The wool insulation can also provide an acoustic barrier which can be good if you are using your space for music production, DJing or using noisy power tools.

Read on below to see the different types of insulation I have previously used in my garden buildings.

Insulating the windows and doors

There are a few key ways to improve thermal insulation in your windows and doors.

1. Replacing the doors and windows for double-glazing units is the best way to insulate your building. You can easily fit house-quality (uPVC) windows and doors into your garden building. I have fitted these windows and doors to my really simple shed.
2. Enhance your current windows and doors with secondary glazing, a cost-effective solution that you can install yourself. It can be customised to fit any window or door shape and can boost thermal efficiency by up to 65%.
3. I’d recommend using rope caulk to help seal any gaps in the window and door frames. This will help prevent heat from escaping through obvious spaces in your building.

Insulating the floor of your garden building

This can be tricky if you are unable to access underneath the building. If this is the case the only real option is to insulate on top of the existing floor. This will mean raising the floor which can also create a problem. The best way to approach this is to lay a thin (but good insulator) 3-4mm underlay and put a reasonably thick floorboard down. I have previously used a gold standard thermal underlay before which is perfect for this situation.

If you can access underneath the building, then the best idea would be to install a thick 100m foam board insulation sheet. These can fit in between rafters, or a small sub-base can be built to house the sheets. It doesn’t have to be 100mm, but the thicker the better.

Here is an image of my garden room build. I installed an extra layer of foil-covered bubble wrap underneath the floorboards for an extra layer of insulation. This extra layer of insulation is great, especially in the wet and cold British climate, and these voucher codes can save you a bundle on it too!

When insulating a garden building floor. try and add several layers of insulation for the best results. Warm air will be trapped between each layer for better thermal efficiency.

Read all about the different types of shed bases here to get an idea of what is possible when trying to insulate your shed base.

How to insulate a shed floor

A shed floor will differ slightly from my garden office build. You might not have access underneath, so the only option is to insulate on top of the floor. You can do this effectively, but the floor’s thickness will need to increase. This will mean a step up into your shed, which can be fine if you’re ok with a little less headroom.

In the above image, I’ve also used a slightly cheaper insulation bubble roll under the floorboards. Foil-backed insulation rolls are perfect where space is tight. I’ve used these insulation rolls as an addition to other insulation boards. They also help create a vapour barrier to prevent moisture from rising up through the floorboards.

It’s also a great idea to install a good thermal underlay if you are planning on installing laminate flooring in your shed, summerhouse or garden office. I decided to use this gold foil-backed thermal underlay which is a great insulator. It’s a bit more expensive than other types of underlay but it’s worth spending the extra for that additional thermal insulation.

This thermal gold underlay will cost you about £75 for 15m² and is thicker than a standard 3mm underlay. This one is 5mm thick and covered with a gold foil moisture-proof barrier. Laminate flooring can be installed directly on top without the need for any adhesive.

Now my garden office has two layers of thermal insulation which is ok for most of the year. If you have the option to install the foam boards before your garden building has been constructed then I would highly recommend it.

What Type of Insulation is Best for a Garden Building?

Garden buildings typically have thin wooden walls and are therefore not great insulators. To help improve this, we can make them thicker, add foam or wool insulation and create a watertight, airtight barrier. Here is a cross-sectional view of a well-insulated garden building.

I have successfully insulated two garden builds now. I used different insulation for each project based on research into the best types to use in each situation.

For my first project, I needed an insulation that could provide both thermal and acoustic insulation. The best product for this application is a Rockwool RW45 insulation slab. These come in 3 different thicknesses: 50mm, 75mm and 100mm. You will need to decide which is best for your project. How much interior space are you willing to sacrifice to insulate your building?

Here is an image of the 50mm Rockwool RW45 shed insulation being installed in my DIY garden shed.

The second project was to insulate my BillyOh Kent garden office. For this, acoustic insulation wasn’t a big priority so I decided to go with a 25mm Celotex insulation board. The thinner 25mm insulation was selected because I didn’t want too loose much of the 4x3m interior space.

The other great thing about this board is that it also acts as a vapour barrier, preventing moisture from reaching the inner walls, which in this case was a 12.5mm plasterboard.

The walls for each project were covered with plasterboard and plastered for a perfect seal and smooth finish. If you don’t go with the foil-backed sheet insulation, then it’s a good idea to seal your walls with a vapour barrier, which will help prevent mould and moisture from building up behind the plasterboard. This should be installed on top of the insulation before the plasterboard is fitted.

How to Insulate a Garden Room

I’ve written a comprehensive guide here for those who want to know everything: How to Insulate a Garden Room Properly: Vapour Control, Materials & Best Practice

Read on for a good detailed overview.

A garden room or garden office is usually built to accommodate thicker insulation in the walls, floor, and roof, making it easier to insulate than a shed or summerhouse.

Garden room walls are typically constructed with 89mm timber battens, allowing more insulation options. For best results, use a combination of foam board insulation (such as Celotex) and Rockwool. This provides strong thermal performance from the foam board and effective acoustic insulation from the wool. In most cases, you can fit a 50mm foam board and 50mm wool insulation within the 89mm cavity.

Starting from the interior, here is a list of materials that make up the walls of a well insulated garden room:

1. Paint on 12.5mm plasterboard
2. Timber frame constructed from 89mm C16 timber
3. Within timber frame – 50mm Rockwool RW45
4. Within timber frame – 50mm Celotex boards
5. 18mm OSB 3 boards
6. Breathable membrane
7. Furring strips
8. Cladding – Ideally a redwood cedar cladding at least 18mm thick

The floor should be similar to that listed above with a timber frame housing 100mm foam boards, topped with 18mm P5 flooring chipboard. P5 boards are ideal for this application due to their moisture-resistant qualities.

A garden room roof could take many different shapes, sizes and styles but here is a look at a well insulated pitched roof.

Further insulation can be added to the interior but this will depend on the overall look and feel of your personal project.

How to Insulate a Shed

Sheds are typically constructed from panels made out of a thin cladding, fixed to a thin timber frame. This can make it tricky to insulate. My advice would be to bridge this gap with a thicker timber batten and create a larger gap that can house the insulation boards.

In most cases, a flat-pack shed will have framed panels constructed with 25x25mm batten timber. If you attach a 25x50mm batten timber on top of this you will seal the gap and create this perfect void on the panel to which you can instal some 50mm foam insulation panels.

Red markers indicate additional batten – Blue indicates where thermal insulation boards are added

Add 25x25mm battens to the existing frame where needed, then cut insulation panels to size and fit them into the gaps. Finish by fixing interior panels over the top to seal the space.

For interior walls, use plasterboard, chipboard, or plywood for added strength and insulation. Thicker boards provide better thermal performance, and leaving a small air gap can help trap warm air and improve efficiency.

Most garden sheds are built from thin 11mm spruce, which offers poor insulation. However, there are several effective ways to improve the thermal performance of even the thinnest shed.

How to Insulate a Summerhouse

A summerhouse differs from a shed or garden office mainly because it usually has more windows and larger doors. Since around 25% of heat is typically lost through windows and doors, a summerhouse can lose up to 50% of its heat if these areas are not insulated.

Upgrading to double-glazed windows and doors will significantly reduce heat loss. Adding draught-proof seal strips around frames also helps stop warm air escaping through gaps.

The rest of the insulation process is similar to insulating a shed. Insulation panels can be fitted to the walls, floor, and roof, then sealed and finished with cladding, timber boards, or plasterboard.

An insulated summerhouse becomes a versatile, year-round space, ideal for relaxing, working, or creating a multi-purpose garden room.

Planning permission for an insulated garden building

Just remember, if you are planning on insulating your garden building to sleep in, you will need to apply for planning permission. Even if you are thinking of sleeping in there a few times a year, you will need planning consent from your local council authority. You can read more about planning permissions for sheds in my other post. Click the button below to view the full article.

How to keep your garden building warm

With the addition of insulation, your garden room will now be able to retain heat much more efficiently. You now have to consider how you’re going to produce the heat in your outdoor building. To do this cost-effectively, you’ll likely want to avoid expensive electric heaters and consider a wood-burning stove or even a gas-fired heater.

If you already have a good source of wood, then a wood-burning stove is going to be a sensible option. It will have the highest up-front cost, but will be inexpensive to use in the long run. The fire might take a little while to get going (15-30 minutes) and will require attendance every hour or so, but it will produce plenty of heat all day long.

A portable domestic gas heater will give you instant heat, which is easy to control. Gas can be sourced locally, and a single bottle will last you many hours. Typically, a 15kg butane gas bottle used on a low setting will last 147 hours and 73 hours on a medium setting.

In comparison, an electric heater will cost more, especially with energy prices as they are now (Jun 2022). You can read more about costs in this useful article.

How Can I Insulate my Shed Cheaply?

If you are trying to achieve this project on a budget, then there are ways to do this. If you are looking to save some money, then consider using packing materials and recycled clothing to insulate your roof or walls. Polystyrene is a great insulator, and if you can save enough, it can be used to pack out the walls and roof cavity. This can, however, be a time-consuming process. Ask friends and family to collect it for you, or look on FB Marketplace for any freebies. You can also look in your loft for any excess insulation. I’ve been in many lofts with way too much insulation stuffed in. (Not sure if builders have overcompensated for something?)

For my garden office, I was stuffing the ceiling void with clothes, packaging, soft insulation and polystyrene from deliveries, which makes for great insulation. We also used some recycled packaging from our frozen meal delivery service, which was amazing. It’s made from recycled jeans. You can just see it at the top of this image.

Bubble wrap can also act as a good insulator. The small bubbles trap warm air, and with a few layers can be very effective. A layer of foil thrown in the mix is also very beneficial, although I’m not sure how many rolls you’d need!

Old clothes can be utilised to insulate your garden room, but they will perform better when shredded. I have previously used recycled packaging materials made from shredded jeans. They are a great insulator and are never in short supply.

What is the best material to line the inside of a shed with?

As you can see, I have converted a shed into a warm workshop and a garden building into a functioning office. So, depending on your desired use, you may wish to have different materials to line the inside.

An office will look best when finished with skimmed plasterboard, but a workshop or gym might benefit from something stronger, like plywood or OSB boards.

That’s all for now. Insulating a garden room, shed, or summerhouse doesn’t have to be complicated or expensive and can give you many returns. I hope you have found this guide useful and will now be able to make better use of that garden building.

Thanks for reading. Check out more great projects.

Further Reading