Options regarding an insulated garden room/workshop?

[kentar]

I'd like to install a garden room/workshop, roughly 4mx6m with a bifold door on the short side. I don't think I need any windows. Not sure what kind of roof style to go with just yet.

I don't want to spend the next 6 months building it, so I was considering a pre fab and knocking it out within a couple of weeks. The trouble is I can't find what I want for what I deem is a reasonable price to performance. Everything I look at seems to be made of 3x2's, whereas I'd want 4x2's at a minimum. 

 

I've thought about buying a shed and then insulating it internally. Here's an example of something I was considering:

https://www.nordictimberbuildings.com/product/20-x-10-pent-garden-summerhouse-with-bifold-doors/

 

£7400 is a ridiculous price considering something just slightly bigger, without aluminium windows and a bifold door is £3.5k. That's almost a £4k difference. I don't get it. 

https://www.nordictimberbuildings.com/product/20-x-12-apex-garden-shed-workshop/

 

I reckon I could build the first option myself with insulation and using 4x2's for £3k. Of course you can build it yourself for less you say... I don't mind paying a fair price, but I feel like i'm being robbed with what's on offer. 

As I said, I don't want to devote a great deal of time to building it myself. Which leaves me with having to buy one pre made, or having someone build one for me.

 

I asked a chippie for a ballpark price and he came back with a figure of £10k. Again, I feel that's taking the piss. I've seen a lot of professional builds on youtube, and they don't take more than a couple of weeks - were talking fancy looking buildings here. I just want a notch above a basic shed.

 

So then I looked at SIPs. I can't find the correct size on the website, but something half the size of what I want is around £3k. So roughly £6k for the shell and a couple of grand to finish it off. That would give me something substantially better than the first option, and I wouldn't have to faff about with spending more time insulating and boarding it.

https://www.simplysips.co.uk/product/4-2m-x-3m-sips-kit/

 

£8k is more than I'd like to spend so I'm interested to hear your thoughts on this. What's my best option? Is there anything I haven't considered?

 

 

 

 

 

Edited Monday at 23:29 by kentar

[Redbeard]

11 hours ago, kentar said:

I'd like to install a garden room/workshop, roughly 4mx6m with a bifold door on the short side. I don't think I need any windows.

 

How will you ventilate the 'shed'? If you might want from  'just a trickle' to 'just a bit more than a trickle' put a small window in. You can't leave a bi-fold a little bit open and go out (AFAIK) with any degree of security.

 

If you think you can build it yourself I would build it yourself. You will get what you want (or what you think you want as you start building, anyway), not just something 'not too far away' from that. Check out the insulation detailing and membranes etc. v carefully and build scrupulously tight.

 

Some will disagree but I see SIPS as sometimes the wrong answer to the wrong question.

 

You could consider building a frame and externally insulating and rendering it. All finished in one go.

[Iceverge]

For speed an insulated metal panel kit is probably the fastest. 

 

https://www.insulatedpanelstore.co.uk/garden-rooms?srsltid=AfmBOoqRKgKk5A49VJzAw4UAI0A1Qrr_WqlDy83VP-C2g0KhavY7zK4x

 

For cost you'll stick frame it on site yourself a lot cheaper. 

 

Liam has some tutorials here. He does a DIY metal insulted panel recently too which looks economical. 

 

https://youtube.com/@thegardenroomguru?si=F75UkGxu67eeS0py

 

I wouldn't use PIR between timbers ever though, too fiddly to get right and lots of waste. Mineral wool is a better option in my view. 

 

 

What people forget to do is. 

 

1. Add appropriate ventilation. I have a dMEV fan in my office. About £70. Same as @JohnMo. I couldn't recommend it enough. 

 

2. Appropriately Airtight the building. 

 

If you do these things you can heat such a small room warm very quickly with a fan heater. 

 

I did a suspended timber floor in my office. Wouldn't do it again, everything rattles. 

 

@Nickfromwales did an insulated slab I believe although it was shrouded on secrecy........

 

 

 

 

[Nickfromwales]

Nah. Gave up on the ground bearing option and it’s on stilts, and uninsulated as I knew it was on ‘borrowed time’. 
 

Outbuilding no.2 will be done better but a couple of fan heaters makes it perfectly comfortable tbh. I just make it very draughtproof so the wind doesn’t blow through it. 

[Iceverge]

I think my next one is going to be insulated slab too with external insulation ( problem rockwool)on timber frame with the sheathing taped as airtighess layer. I should get an exceptional envelope with that. 

 

 

 

[SteamyTea]

On 12/08/2025 at 00:05, kentar said:

^{but something half the size of what I want is around £3k}

That will be a 2m by 3m shed  so an area of 6m²

You are after 4m by 6m, so 24m².  4 times the size, not double.