Anyone built an insulated outbuilding /studio?

[Lolly567]

We’re currently looking at houses. Today saw one online that had a detached outbuilding (6x4 m) in the garden that the owners used to use for a gym. It suddenly made me think that such a thing would solve many of our problems (I work from home and have people coming and going, so it would be fantastic to keep all that seperate from our actual house.)
instead of adding that to our criteria when searching for a property (unfortunately this property is already under offer) I thought we could buy somewhere with a big enough garden and build our own.
I’d want to do it as cheaply as possible but also I would want something substantial that doesn’t just look like I’m taking clients into a shed. 5x4m would be big enough, it would need to be insulated and have electricity and heating. I’m thinking wood as it would seem best value. Has anyone built anything similar and have any idea about costings?

Bumping in case anyone can help!

Have a google about garden offices or garden rooms. Look at the planning portal rules too about how big you can have it in relation to boundaries and that an outbuilding is not allowed to be used as another 'habitable' i.e. sleeping room.

Wooden ones seem popular now but from initial investigations they seem to cost as much as building a brick one, which would last a lot longer. Wooden ones stat off looking good value until you add in the extra insulation, electrics etc.

£10k seems a ballpark figure for a 4 by 5 metre garden shed room. but fitout, electrics, build costs all vary.

Or there might be a garage that you can make into a room. You can give it its own entrance and bell.

Yes, I've done many (used to be Director of a timber frame company that manufactured them).

Timber frame insulated with PIR (Kingspan/Celotex) insulation is the way to go, but you need to decide how far you want to go with longevity vs. cost.

On a 'proper' timber frame construction, you have a ventilated gap behind the external cladding, then a 'breather membrane' (basically a breathable waterproof fabric) on the outer face of the sheathing on the timber frame itself.

Then on the inside of the timber frame, you have a sheet of polythene, called the 'vapour barrier', whose job is to stop any moisture from the warm air inside the building from getting into the wall structure, where it cools down and the moisture condenses out, causing the timber frame to rot.

The extra complication of doing it properly increases the cost substantially, so you need to decide whether it's worth it for you, or whether you're happy to simply accept that the building will have a limited lifespan.

You need to avoid the need for Building Regulations compliance, which means keeping the floor area below 30m2 (so 6x4m. is fine) and at least 1m. from any boundary (otherwise there are complications with using timber cladding, due to fire risk). If Building Regulations kick in, you've got problems... not only will they expect compliance with fire regulations and the moisture-proof construction described above, they'll also require structural calculations to prove that the timber frame is adequate.

If you can, you also need to avoid the need for Planning permission, by sticking to the rules on 'Permitted Development'.

Cost is a piece of string, but depending on design and construction quality, and how much work you put in yourself, could run anywhere from £3k to £30K.