Are you thinking of converting an existing garden building into a functional space that can be used all year round? That’s exactly what happened to me and I’ve decided to document the process and share my experiences with you. I insulated a shed a couple of years ago and more recently my garden office log cabin. The process is quite straight forward and most will be able to accomplish a much warmer, functional living space that can be enjoyed all year round.
By adding insulation to garden rooms you will accomplish two things. Firstly, you are going to help improve the thermal efficiency of the building. Any heat within the building will be trapped inside and will seep through walls, floors and ceiling much slower. This will help keep heating bills to a minimum. Secondly, this process works in reverse. During the summer heat from the sun will be reflected away from the building keeping the interior cooler. I think that’s pretty clever.
Within a normal house, heat is lost through the different areas of the house. A garden building is quite similar to this. Here are the percentages you could expect:
- 25% through the roof
- 35% through the walls
- 10% through the windows
- 15% through the doors
- 15% through the floor
As you can see heat is lost in all directions, so it’s important to cover every aspect of your garden building.
Garden sheds are typically made with thin 11mm spruce wood. Not a great insulator! There are however many options for increasing the thermal efficiency of even the thinest of sheds.
In this article I’m going to cover: How to insulate a summer house, how to insulate a shed and how to insulate a garden room. Basically you will be able to insulate any garden building with these techniques.
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 use noisy power tools.
Insulating the windows and doors
Replacing the doors and windows for double glazing units is the best way to insulate your building. Single glazed unit can sometimes be modified with double glazing so you might not need to replace the whole door or window. If you are going all out then you should also be able to fit house quality windows and doors to your garden building. I have fitted these windows and doors to my shed which was really simple.
You can also use rope caulk to help seal any gaps in the window and door frames. This will help prevent heat 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. In the above image you can see I’ve also used a slightly cheaper insulation bubble roll under the floorboards. Foil backed insulation rolls are prefect 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 rising up through the floor boards.
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 section view of a well insulated garden shed I built a couple of years ago.
I have successfully insulated two garden builds now. I used different insulation for each project based on research into what the best types were to used 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?
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 as I didn’t want too lose too much of the 4x3m interior space.
The walls for each project were covered with plasterboard and plastered for a perfect seal and smooth finish. It’s also a good idea to seal your walls with a vapour barrier which will help prevent mould and moisture building up behind the plasterboard. This should be installed on top of the insulation before the plasterboard is fitted.
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 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. Find out more on the Calor website.
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 over compensated for something?)
Bubble wrap can also act as a good insulator. The small bubble 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 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.
That’s all for now. Insulating a garden room, shed or summer house 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.
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