Garden Outbuilding - Is this right?

[J4mes]

Building an outbuilding which will be a gym, so it will be used occasionally for an hour or two per day. We have planning approved, dimensions 3m x 4.8m overall height 3.65 with a pitched tiled roof.

 

I think I may be going overkill with the building specification so wanted to see if anyone can advise. It will be under 30sq meters so doesn’t need building regulation approval.

 

Been quoted for a slab base 300mm thick with reinforced steel mesh and fibers. The quote for the walls is for double skin blockwork 7N outside and thermalite inside. Outside will be rendered and painted.

 

Pitched roof will then be added and it will be tiled with Redland Concrete tiles to match the house.

 

Regarding the walls, could these be single skin? Or would that cause issues with condensation / damp. I would be happy to insulate the inside if it meant I could have a bit more space, at the moment I will be losing around 600mm plus paster board width, so the room ends up being 2.35M wide ! 

 

Any advice would be really appreciated.

Regarding the walls, could these be single skin? Or would that cause issues with condensation / damp. I would be happy to insulate the inside if it meant I could have a bit more space, I will be losing around 600mm plus paster board width, so the room ends up being 2.35M wide ! 

 

Any

[markocosic]

That's garden shed size...

 

I would timber frame something that small to avoid the loss of space whilst retaining some insulation.

 

You can still use render board on the outside and render it for visuals/fire. You can still put tiles on the roof.

 

45*95 studs would work at that size. So walls 15 mm plasterboard, air barrier/vapour retarder, 95 mm wood with mineral wool insulation between, roofing membrane to shed water, 25 mm roofing battens to create a drainage plane, say 25 mm render board and render and allowance for wobbles. Gives 160 mm total for similar insulation value (95 mm of insulation)

 

145*95 studs would be toasty. Or probably better stick with 95*45 studs but put a 50 mm layer of foil backed and seam taped PIR/PUR on the inside.

 

Ridge beam and cathedral roof to give impression of space? Windows?

[gc100]

Surely in something that size you don’t want any insulation if it’s usage is a gym?? 
 

[Chanmenie]

Save yourself a fortune and as previous comments, build with timber frame and consider cladding instead of render. 

[JohnMo]

I would buy a garden room something like 70mm log building. Some insulation in the roof and floor. Only requires a simple foundation. Everything required in a single package.

[joe90]

  On 20/09/2023 at 07:30, JohnMo said:

I would buy a garden room something like 70mm log building.

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I have just put up a log effect garage, 44mm timber and it looks really good, pretty in fact which is nice when it’s in your garden, I can recommend “quick garden” and I am contemplating a garden sun room next year. Also I will be using ground screws for mine, no foundations. Even the 44mm timber has some insulating factors and as said above why would you insulate a gym, you will be working up a sweat. Here is an example.    https://www.quick-garden.co.uk/summer-house-clockhouse-4m-x-3m-13x10-ft-44-mm.html

[Andehh]

Forget extra insulation, just stick in cheapest air con unit you can find!

[J4mes]

  On 20/09/2023 at 05:57, markocosic said:

That's garden shed size...

 

I would timber frame something that small to avoid the loss of space whilst retaining some insulation.

 

You can still use render board on the outside and render it for visuals/fire. You can still put tiles on the roof.

 

45*95 studs would work at that size. So walls 15 mm plasterboard, air barrier/vapour retarder, 95 mm wood with mineral wool insulation between, roofing membrane to shed water, 25 mm roofing battens to create a drainage plane, say 25 mm render board and render and allowance for wobbles. Gives 160 mm total for similar insulation value (95 mm of insulation)

 

145*95 studs would be toasty. Or probably better stick with 95*45 studs but put a 50 mm layer of foil backed and seam taped PIR/PUR on the inside.

 

Ridge beam and cathedral roof to give impression of space? Windows?

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Thanks for the reply. Originally we were going to go with prefabricated timber summerhouse but in the style we wanted it was coming out around £12k which seemed a lot for a timber building that would deteriorate and need yearly painting. I thought something built of blocks with a tiled pitched roof and UPVC double glazing would be more of a long term investment and we could match to the house etc. Looking like £15k would get me almost there… 

 

Maybe we are over engineering it though, especially if we end up losing 300mm on each wall. 

[J4mes]

  On 20/09/2023 at 07:20, gc100 said:

Surely in something that size you don’t want any insulation if it’s usage is a gym?? 
 

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Well we thought if it’s brick built with tiled roof, UPVC windows etc then might as well insulate and then could be used as an office etc in the future if we needed to. 

[markocosic]

  On 21/09/2023 at 16:42, J4mes said:

seemed a lot for a timber building that would deteriorate and need yearly painting.

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How often do you paint your roof timbers?

Never. They're dry under the tiles.

 

Ditto a timber stud wall with cladding that isn't timber.

 

Sheds with a timber finish do need painting and can't be heated without composting the roof if that's underneath the felt.

 

There's a difference between these and something built more like a house though.