Another garden office AKA posh shed!

23 Jul 2015
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United Kingdom
Hi all. Reader for a while; first post! I'm 'sure' you would all love another self-build garden office thread so here goes...!

I've been researching the building of an office/rec space with attached shed at the end of our garden, since my wife and I found out the amazing news that our first child is on the way. (Being booted out of my current man cave in the house!)

There's an existing concrete slab from the old shed, which I can see is 80-100mm, in good condition and level. I'd like to use this base and continue outwards, and could lay a new slab (joining appropriately, etc) or use 'pad' foundations. I favour the latter as we're mid terrace with no easy access, I've never laid concrete (probably not that hard mind) and pads wouldn't be much different cost-wise.

On the image below, the top/right/diagonal black border is the fence, and the existing concrete slab is show in blue.

Red outlines the proposed structure. The shed area will be on the left, and office on the right with access via sliding glass upvc doors, plus a high slit/lozenge window on the 3m office wall at the top giving light over the 6' fence. Shed will hold my hand tools, garden power tools, few other bits and pieces... nothing too heavy. Office will be desk, IT stuff, small filing cabinet, etc. Again nothing too drastic.

Bit of an awkward shape and pushing up to boundary as much as possible, just leaving enough access to attach cladding, etc. As such the max height will be 2.5m to keep under permitted development. The office side will be the usual PB > vapour barrier (or foil backed PB) > timber frame with insulation > breather membrane > battens > cladding plus EPDM roof.

A few questions:

- Any problems foreseen having a timber framed floor starting on the concrete slab (counter battens underneath for ventilation, DPC tape under battens) then continuing on to something like EasyPADs: ?

- Height inside the 2.5m structure will be at a premium on the office side (6' 2" myself) so planning on level internal ceilings and top plates, etc then firrings to get pitch. This would seem to lean towards a cold roof system over the office area with plenty of ventilation via soffits?

- Should I wrap the whole structure in breather membrane? It should be dry due to the EPDM, and BM around the exterior walls... but some moist air would inevitably enter the shed area though a 'shed' style door and other gaps. Not direct rain, but still...

- Alternatively, I could BM the entire structure but also the office wall inside the shed ensuring that it's well lapped and taped to the external BM?

Thanks again! :)

[Edited 27/07]
Last edited:
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If I'm asking the wrong questions, or the right questions in the wrong way, do say... :)
The post is so convoluted I wouldn't know where to start advising. And the description of what you are actually proposing is not clear and neither is your drawing.

So in short re-do it, make the drawing clearer and ask less but more specific questions.
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Thanks for the feedback FM and fair point! Have pretty much discounted some the thoughts above so I'll edit the post shortly. Will do a proper sketchup model soon too...
As a follow-up to the edited original post, with reference to joist sizes (and having looked at span tables) if it were possible to use 2x4 in the floor rather than 2x6, this would add precious mm of additional internal height.

Mostly leaving aside the shed portion (2x4 being way over-speced for a bog standard shed) I am thinking of doubling a couple of 2x4s along the 3.6m length between office and shed, giving extra strength for the internal wall above it. EasyPADs as linked above would be placed at each end of the 3.6m, plus one in the middle at 1.8m ... a little less than the ~1.9m max span for a 2x4.

Then two more EasyPADs on the other side of the shed, and on the diagonal corner. Maybe one more in the middle of the lower shed area.

With 18mm OSB on top, and at 400mm centres, would this be sufficient to prevent 'bounce'?

I suspect it may also be better to increase the width of the 3.6m joists (to increase the max span) and instead place the EasyPad at the point where the shed comes across to meet the office, 2.1m from the top?

Thanks in advance.

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