Pent roof workshop/shed planning

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16 Feb 2024
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West Sussex
Hi all, first post after some long-time lurking gathering ideas for a new DIY garden shed/workshop.

My plan is for a 2.8m (depth) x 3.2m (width) building with a single pitch roof sloping front to back. I'm limited for size by the width of the garden (4.0m) and slightly complicated by the end of the garden not being square, so I may end up with a structure that's a little deeper on one side than the other - I'm still undecided about that. Main use will be as a 'clean' shed (so no dirty lawnmower or muddy tools), bike storage, DIY workshop and bike workshop.

Current plan is framing the walls with 2x3, and 2x4 for the floor and roof. Insulated floor, walls and roof, with Kingspan or similar in the floor and fibreglass or other 'soft' material in the walls. I intend to clad the sides and back with corrugated bitumen sheets, and the front with timber of some kind. The roof covering is tbc, but ideally I'd like something with better durability than simple shed felt.

Couple of things I'm still unsure about: depending on how high I want the back wall I can either have a 10 or 6 degree slope on the roof. Is 6deg too shallow to allow good runoff and would I limit myself to certain types of covering?

Also, I still can't work out the best way to layer the walls. Whether to skin the outside with OSB, wrap with breather membrane then clad. Or whether to line the inside with OSB (to act a vapour barrier and just membrane/batten/clad the outside?

I shall keep pouring through threads to harvest advice, but in the meantime any suggestions gratefully received. Thanks

Edit: oh yes, my other question was whether 400mm centres for the wall studs was necessary or if 600mm would be ok if either the inside or outside was being skinned with OSB anyway?
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Can you get SIPs
For a workshop, I'd want sheet on the inside so that I can have a ton of shelves for vertical storage.
SIPs give you inside and outside skins plus insulation all in one rigid panel.
Just add battens and cladding on the outside.

EDPM rubber for the roof. One piece. No seams to leak.
I’ll sheet the inside anyway. My preference would be something other than OSB on the inside purely for aesthetics, but it’d get painted anyway. If it’s ok to just have cladding>membrane>insulation then I’d probably go with that.
I would just build it all with 4 x 2`s this way you can get 100mm cavity batts in the void (way cheaper than Kingspan and good sound insulator ).
That roof pitch is fine I have recently done an EPDM one and a metal over osb one. I think for a single pitch I prefer the metal sheets, very quick and easy to do and no sticky glue involved.
I would not use corrugated bitumin sheets because they are pretty fragile.
The very cheapest cladding material per M2 I found was regular galvanized corrugated iron, just screw it on with roofing screws, the advantage here is it will add some stiffness to the walls where I doubt the onduline will.

If you are going to insulate then from inside to outside it is. Ply/osb, vapour barrier, stud wall with insulation, breathable membrane, battens, cladding.

As Ollie78 said, Rockwool batts are much nicer to deal with than kingsman/ PIR insulation. Also PIR insulation value is heavily reduced by poor fitting, use gapotape if you go the kingspan route.

With anything below 14degrees you’ll have to go with a continuous membrane/sheet roof solution. The flatter you go the greater the likelihood of rain being blown over the other three edges, just factor this risk in to the placement of the shed. EPDM is my flat roof membrane of choice but only as I’ve used it happily a number of times. Others advocate for GRP or metals sheet and I’m sure they also work well, the secret is say is as much good fitting as a good system.

If I were to be building any garden building now, I'd either use the SIP's as previously suggested, or I'd go with the metal insulated panels like they use on industrial buildings. They come in a range of colours as well as insulation depths so you can get decent insulation with decent strength. The internal finish is clean and requires no additional painting so thats time saved. They're also really solid and can span considerable lengths for the roof. Cost wise, when I priced it up, it worked out as cheap as building a roof and then retrospectively adding insulation, battons, boarding etc. And the time saving would have been considerable. Cladco was the website I'd used to get the price. I only priced it up as a concept for a friend so I didn't use them. However I've seen a number of YouTube videos using them and they "seem" relatively easy to use
For the roof, I would go for either metal, insulated panels or GRP (Flexitec 2020) on T&G osb. Both options much more durable than felt or EPDM.
Check and see if you have a supplier of profiled sheet material locally. If you have, they will run off wall sheets (reverse of roof sheets) to your precise length. Much superior than Onduline.
Thanks all, solid advice and much to contemplate.

I’m guessing there are no benefits from using planed framing timber over rough sawn other than it’s nice to handle. (I’m assuming sawn will be less expensive than planed profiled framing timbers.)
currently building mine (you can see my progress on my thread)

Im using 18mm OSB for inside and outside sheathing, probably could have gotten away with thinner but there was much price difference where I am, also like that I can mount storage anywhere on the inside with the OSB

Ill be doing a EPDM roof, you can buy offcuts of the rubber sheets from ebay, my roof is 5m x 3m and I got a 7m x 5m EPDM offcut saving me about £100 . I bought the rest of the materials for it from permaroof in a kit and told them to remove the rubber as not needed

sawn or planed doesn't matter, just preference, its all the same wood, depending if you get c16 or c24. I wouldn't have like to build with sawn though, splinters galore!

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