BillyOh garden office interior

How to insulate your BillyOh garden office log cabin

In my previous post, I described in detail how to build a BillyOh Kent garden office log cabin. Now I’ve made progress on the building and it’s ready to use as a fully insulated garden room, complete with electrical sockets, lighting and heating so that it can be used all year round in comfort. Read on to see how to insulate your BillyOh garden building.

This specific building is the BillyOh Kent Garden Office.

BillyOh Log Cabin Garden Office

The BillyOh Kent garden office is a great building designed and produced by Kybotech Ltd. based in the UK. It is a customisable garden building available in a number of different sizes at a very reasonable price. That’s what makes it so appealing. We wanted a workspace in the garden but the costs of a professionally built garden room was a bit too scary. So I challenged myself to build my own for a fraction of the cost. In total this build has cost us about £5800 whereas a similar size build from a garden building company would cost in the region of £20,000.

Visit my BillyOh Kent building post to see this build from start to finish. I have included links to all the materials used within this project. (links will open in a new tab)

How to insulate your BillyOh log cabin

For my building I decide to use a 25mm Celotex insulation board. These boards provide a good level of insulation, are easy to work with and are cost effective. You can get thicker boards but I wanted to retain as much of the interior as possible. Another good alternative is this Recticel Instafit Polyurethane Insulation board.

Firstly I fixed some 25x50mm battens around all the corners of the building. This is where the plasterboards would be fixed to. Make sure you run these around the whole interior edge. See below image. (50mm side flat on the surface) This timber from B&Q is also suitable.

log cabin interior 25x50 batten

For the wall corners you will need to put two lengths next to each other so that there is a fixing point on both walls. Here is a cross section view for the corners timber frame.

cross section wooden frame recess

This will create a 25mm deep recess in which the insulation boards can be fitted. The insulation boards can then be cut to size using a sharp knife. I used a utility knife for this. I measured up the height of the recess, marked it out on the board with a pen and cut with the knife.

celotex insulation board for garden office

Save any off-cuts at this point as they will be required later on.

I continued around the room with the same process. Measuring and cutting to fit in the recess.

celotex insulation boards log cabin

The boards are not fixed to the wall at this point. The plasterboard will hold them in place later.

I worked around the main incoming electrical cable. This was a thick cable. I cut out some pieces of Celotex to fit around the cable making it as neat as possible.

celotex insulation around cable

I continued fitting insulation boards all the way around the room. Cutting sections to go around the windows and door frames.

You will notice that the window and door frames are about 20mm thick which isn’t going to work when fitting the plasterboard. Therefore I cut some 5mm strips of wood to go around the frames to bring them up to 25mm. (The same as the rest of the recess framework.)

I also cut another piece of wood (25x30mm) to fit around the frame which would create a barrier for the plaster to sit up against. These pieces were nailed into place with some thin lost head nails.

windows frame insulation

Fitting the electrical cabling

I decided to fit the electrical cabling for the sockets after the insulation boards were fitted. This would be easier, rather than trying to measure and cut the insulation boards around the cables.

A channel was cut into the insulation board using a sharp utility knife. The socket back boxes were then measured up and cut out using the same knife.

wiring sockets garden office

All cables ran back to the main fuse box. (Consumer unit)

main fuse box garden office

I have a lot of off-cuts left over from the insulation boards so I decided to fill the ceiling with these. There was almost enough to cover it all.

Fitting the plasterboard

Before you go any further it’s a good idea to fit a vapour barrier to all the walls. This will prevent moisture building up behind the walls which can cause issues with the plasterboard.

With all the insulation fitted, cables run and frames modified it was time to move onto the plasterboard. Measuring and cutting the plasterboard is similar to cutting the insulation boards. However, you won’t need to cut all the way through a plasterboard sheet. Simply cut one side and then snap the board along the cut line.

fitting plasterboard

The plasterboard is fixed into place using drywall screws. I used 35mm screws around the edges, were the boards sat up against the wooden frame. I then used 50mm drywall screws to fix the centres of the boards. It’s important to make sure all the boards are fix securely. Any movement can crack and crumble the plaster once skimmed.

cut plasterboard around window frame

Cutting plasterboard around window frames was a little more difficult. As in above image I had to cut all the way through the board. i couldn’t use the cut and snap technique as before.

Light switch and socket back boxes can then be measured and cut into the plasterboard.

light switch back box installation
plasterboard finishing
plasterboard around window frame log cabin
plasterboard finish around window frame

Plastering the interior

With all the plasterboard now fitted it’s time for skimming the walls. I hired a professional for this as they can do it to a high standard much quicker than I can. The cost for this was £250 for all the walls. It took him about 6 hours to complete the whole lot.

It’s important to let the plaster fully dry before painting. This can take about 5-7 days depending on the weather. Don’t get impatient and paint it before this or it will likely crack. The first two layers of paint should be done with a watered down emulsion (50% water /50% paint)

Here it is after one day. Drying slowly.

plaster drying

With the plaster fully dry it’s time to get on with the painting.

dried plaster

Painting the walls

Following on from the plastering I applied two very wet coats of paint and two normal coats. The first two coats of paint were 50/50 water and white emulsion paint. This prevented the paint from drying too quickly and cracking.

wet paint on plaster

Fitting the laminate flooring and thermal underlay

The underlay I am using for this garden building is a special thermal underlay to add some further insulation to the room. I already had a layer of insulation under the floorboards so this is an extra layer for further thermal protection.

garden room floor clear

After sweeping and vacuuming the floor it was time to roll out the thermal underlay. To help out I used a staple gun to hold the pieces in place.

garden office thermal underlay laminate floor

This roll includes a 100mm overlap so you can create a good vapour barrier. No need to add any extra barrier.

thermal underlay in garden office

With the underlay in place it was time for the laminate flooring. We opted for a thicker laminate board for that bit of extra insulation.

laminate flooring garden office

The final stage was to add skirting to seal the gaps around the lanimate flooring.

garden office skirting

Insulating and finishing the ceiling

As mention before the ceiling is mostly insulated with the same boards as the walls. I did however run out. Rather than buying another board I decided to fill the other areas with recycled insulation materials. This is a great money saving and environmentally friendly approach. I used polystyrene sheets and other packaging materials for this purpose.

recycled insulation material

The whole ceiling was then cladded with a spruce tongue and groove timber. Each piece was cut to length and nailed to a retaining timber runner that ran down the walls and rafters.

It took a while to cut all the pieces but here is the finished ceiling. I’ve also added some more insulation to fill as many gaps as possible.

I’ve now had a good chance to see how this building performs in some real hot weather. I’m happy to say that the insulation is doing it’s job. The garden room stays pretty cool for most of the day. I noticed the temperature creeping up later in the afternoon when the sun was at its hottest. Outside temperature was about 33 degrees whilst inside it reached about 27 degrees. This level of heat was manageable with a 12” desk fan.

Wrap up

So there we have it. How to insulate your BillyOh garden office, shed or log cabin. It goes to show how easy you can transform a garden building into a functional room that can be used all year round. With a little investment, you can achieve this with most of the BillyOh garden building range.

Tool shed side extension

I’ve recently added a small side extension storage tool shed. This provides space for my tools and a few other bits. It’s a great addition and was easy to construct with some 50x25mm timber and some cladding. For the roof, I used some leftover polycarbonate sheets from my veranda build.

My next project will be to install a log burning stove in our BillyOh garden office. Stay tuned for the latest updates.

Here’s a little video tour of the finished building.

Thanks for reading. Please feel free to ask me any questions about this build using the comments section below.

Why not try one of these related posts:

How to insulate your BillyOh garden office


  1. Hi Ben,

    Just looking for a movement and moisture update now you’ve got another couple of seasonal changes under your belt. Anything you’d change if you were doing it again?

    Cheers, Will

    • Hi Will
      Thanks for the follow-up question. I’m happy to say everything is going great with this garden room. Minimum movement both inside and out. There’s been no ingress of moisture anywhere. The plaster around the doors and windows is also holding up really well. I expected these to be the issue areas due to the plaster being finished right up to them but there is only a tiny crack next to one of the windows which can easily be filled.
      There are only two things I would have done differently if I could do again:
      1. I would have purchased the larger 5m x 4m BillyOh Kent. I could do with the extra space.
      2. I would have installed a moisture barrier under the insulation boards. Just for peace of mind. For an extra ~£40 it’s a no-brainer really. (Although the insulation boards on their own are doing a good job of preventing moisture ingress on my build)
      Hope this helps

  2. Hi, really good build project so thanks for the inspiration. One query around guttering, did you install any as part of this to help?

    Also for the roof, did you just use the felt that came with the kit or did you end up replacing this with something better?


    • Hi James, thanks for reading.
      I’ve not installed any guttering yet but it’s in my list of things to do.
      As for felt I just used the standard felt that was provided as it’s quite good quality felt. I will likely end up replacing it with tiles at some point. When the budget allows 👍🏼

  3. This looks great, I’m trying to decide between and log cabin to insulate myself and a fully insulated building from Dunster House. How is the temperature in the winter? Are you using anything to heat it? I want to have it as a recording studio so will be keeping instruments in it. I’m looking at an air source heat pump, but not 100% sure right at the moment.


    • Hi Matt. You’ll need a heating source whatever building you decide to go for. I have a small oil-filled radiator at the moment which is ok for winter but I also have a fan radiator to boost heat output when heating from cold.
      The insulation I used (25mm) isn’t really sufficient for mid-winter but does hold the heat quite well throughout autumn and spring. If I had more space I would have installed 50mm insulation and a layer of Rockwool for sound deadening.
      If you want the best results, you should install this, especially in a recording studio. 50mm Celotex and 25-50mm Rockwool.
      I will be installing a small log burning stove soon as this will be the most cost effective method for heating this small space.
      Hope this helps

  4. Has your cabin had any movement now we’re in Winter? Interested to know if there’s been any water or tanin leaks coming through, or the logs swelling from the wet & cold weather.

    • Hi Karen. Other than a tiny crack in the plaster above the window frame everything is looking great. No issues with moisture anywhere so it’s looking like a good build. Having built a small internal frame to mount the plasterboard I think this has helped retain the shape of the cabin. The insulation boards do a great job as a moisture barrier but you can always add extra if you’re nervous. Hope this helps. Ben

  5. Well done! Great piece of work and awesome final result. What is that foil between roof boards and celotex boards ? Did you use any damp proof membrane in the celling ? Can’t see any. Thanks

    • Thanks Tom. I used a foil backed bubble roll before fitting the roofing boards. This essentially acts as a moisture barrier. The Celotex boards are also a good moisture barrier so I didn’t feel the need to add a damp proof membrane.

  6. This looks really tidy, well done!! I’m curious how are you getting on and how did this cope with the heat this week? I’m looking into options for a garden studio and your posts are a real inspiration for going down the DIY route but I’d want to use it comfortably year round.

    • Hi Alex. Thanks! It been pretty good in the heat. Stayed cool for most the day (with windows closed) but started to heat up a bit in the late afternoons. A fan helped circulate the air for the hottest parts. It reached about 26 degrees at its hottest. I will likely install a mini log burner this autumn in preparation for winter. Shout if you have any more questions and I’ll do my best to answer them. Ben

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