Workshop Design

[kdampney]

Ok, here's our garden, my current workshop design - please feel free to critique - and lots of questions!
[N.B. also posted on the UKW site]

Our garden, perhaps 30m long and 7.4m wide. The hedges at the back and the small shed need to go. There's also a slight slope down the garden, perhaps 1:15. The workshop will fit at the end, just the other side of the whirlygig clothesline.

A difficult corner to navigate around - no mini-digger's getting round that! And probably no loaded wheelbarrow either.

Or something similar. Only some cladding is shown, and I may be able to get some 2nd hand UPVC doors which will change the front layout. Around 3.7m high, 18m2, and keeping 1m away from the boundaries. Will need PP, but won't need BR.

Following Mike G's original design, though this probably leaves a cold zone around the bottom of the OSB as there's no insulation there. Any ideas on how to prevent that? A 2nd skin of thermal blocks? No brickwork at all?

I've literally guessed at the roof, so trusses or a ridge beam? I'd like some storage up there if poss, and there should be 2.3m height underneath, so plenty of headroom.

Questions:
1. Does the slab look sufficient? The soil's fairly firm but not too clayey. There may be hedge roots underneath.
2. Any thoughts on insulation of the bottom part of the walls? A 2nd skin of thermal blocks would mean everything else has to move... Or should I just have the mud sill straight onto the concrete?
3. Are the housewrap, DPM and DPC all in the right place?
4. How do double-glazed (probably UPVC) windows and doors fit into the framework?
5. The roof... Any thoughts on structure?
6. Best choice of roof tiles/EPDM? Which is most cost-effective/easiest to do/most durable?

I'm an enthusiastic DIYer, but have no great knowledge of barn-raising other than what I've read on forums!

Many thanks.

 

[Mike G]

Hi Kes.

Nice drawings!

You'll need 100mm of concrete, not 75, and 1200 gauge polythene on your slab (well, you don't need any at all, but if you put it there, it will need to be thicker). Your OSB only needs to be 9, 10 or 11mm, (see what's available in your area).

The difficulty of trying to have a DPM above a concrete slab is that even a single grain of sand left on the concrete will push through the plastic, so you have to put something down underneath the plastic as a cushion. There are some fleece-type fabrics used by timber floor layers which look like they might do the trick, but I've never used them, and avoid this detail if I can. The DPM under the concrete does a perfectly good enough job, and no matter that this isn't a detail you would use on a house, I would suggest you simply omit the problem by leaving out your second piece of plastic. You can also omit the battens, and just have T&G boards (glued together) floating directly on top of your Celotex floor insulation, held down by skirting.

Don't worry about the cold bridge at the brick plinth. The brick is what makes this building last, so don't even for a second contemplate sitting the sole plate straight onto the concrete. You'll be building a new shed in 10 years if you do. The little bit of cold bridging is unimportant in the scheme of things (although obviously this isn't a detail you could use on a house), but I avoided it on my workshop with a 50mm thick insulating block, and the sole plate sitting flush with the inside face of that. So long as the edge of your slab is a couple of inches or so above the surrounding ground level you won't need to run the DPM up the face of the bricks, either, but as I said, just leave that 2nd piece of plastic out altogether. You can if you have it if want, of course, but you'll find this detail a nuisance, particularly trying to fit the OSB over it, and of course, you'll breech it every time you put a fastening in, such as screws to hold a skirting in place.

For the roof, just give me the span and the angle, and let me know what's on the roof (tiles/ slates/ felt?), and I'll design it for you. One thing I would point out is that it's all very well having a roof void for storage, but unless you have easy access to it you won't be able to use it. So you can consider doors in the gable, or leaving out 2 or 3 joists to give you plenty of room to get up there with long stuff (which is the approach I took).

You're going to have fun building this if you can't get access for building materials. I can't imagine how you'll do the concreting, without hiring an expensive pump.

Anyway, looks good. We'll have fun watching you build this.

What's UKW?

 

[kdampney]

Hi Mike,

Thanks for the detailed response!

If the OSB is thinner, will it still be strong enough to hang things off? I'll probably plasterboard the inside (I'd like it to be good enough quality to be a thought of as a home office or garden room, if we move in the future).

Will Celotex and T&G boards be solid enough flooring for machinery like a planer/thicknesser and bandsaw, without battens? How about with electric underfloor heating running between the two, or is that a bad choice?

I'm tempted to remove the outbuilding just to make it easier to get to the bottom of the garden, but I think that might be a step too far for my wife as we'd lose the tumble drier and freezer. Pumped concrete should be around £550, or I could try making a trolley that can get around the corner, and DIY it...

The roof is around 26 degrees (that can be modified, it's just what I happened to put it at), and the span is 4.8m (length of the top plates). I did leave out a few joists for access, but am not sure what to put on the roof. Are cedar shingles a good choice, or are they very expensive? I haven't got very far with the roof planning!

Thanks so much for all your help.
Kes

 

[Mike G]

Yep, 10mm OSB is fine for hanging light stuff like tools off, and for shelves you just fix back to the studs.

A fully sypported (as this one would be) floating floor is fine for machinery, so long as you use a decent quality insulation such as Celotex, and 22mm t&g chipboard, or, preferably, 22mm t&g ply. Forget the electric underfloor heating. It isn't good enough for space heating (it's main use is to make tiled floors comfortable to walk on in bare feet).

I wouldn't plasterboard a workshop, but each to their own.

Cedar shingles are probably the single most expensive item you can put on your roof, other than thatch. They look great, though. It strikes me that you won't actually see your own roof at all from ground level, so you'd be putting a lot of money up there just for your neighbours' sake , and for the sake of your view from the upstairs windows. I think I'd probably put EPDM up there, or one of the modern corrugated aluminium products, but it's a personal choice.

Just checking....the measurement across the wall plates is 4.8m?

Are your studs going to be at 600 centres? That's as close as they need to be, really, although if you are hanging something massive from the walls you could consider 400 C's. Anyway, rafters should either sit directly above studs, or you should have a double plate at the top of the studwork. The latter allows the rafters to sit anywhere. Again, depending on your roofing material, your rafters only need to be at 600 C's. Assuming this spacing, you can just about get away with 5x2s as rafters, but they cost almost exactly the same as 6x2's, and that would be a better choice.

 

[Wizard9999]

Will Celotex and T&G boards be solid enough flooring for machinery like a planer/thicknesser and bandsaw, without battens?

I have a floating 22mm T&G chipboard floor sitting on that crappy 25mm polystyrene insulation from Wickes. Takes my c.250kg PT fine, even given the fact it is on a moveable base so all the load is concentrated onto four wheels.

Terry.

 

[Doug]

You shouldn't have a problem with planning permission Kes, judging by the monstrosity the council have allowed to be built out of the roof of the house to the right of your photo :shock:

Good luck with your build.

 

[Jimmy Mack]

Great to see more another workshop...(*cough*) I mean garden studio going up! Looking forward to following.

Gook luck,

Jim

 

[kdampney]

Cedar shingles are probably the single most expensive item you can put on your roof...you'd be putting a lot of money up there just for your neighbours' sake.

Very true. We are having a loft conversion soon, so I'll have plenty of free concrete tiles left over, but they're quite heavy aren't they? I was thinking they'd be a bit ugly, but as we won't see them most of the time... They are these type:

Just checking....the measurement across the wall plates is 4.8m?

Yep. That's probably the widest it can be, but if it's excessive from a roofing point of view I can reduce it.

Are your studs going to be at 600 centres?

If that's good enough, then yes, though I suspect concrete tiles would require more...?

I have a floating 22mm T&G chipboard floor sitting on that crappy 25mm polystyrene insulation from Wickes...

Reassuring, thanks Terry.

You shouldn't have a problem with planning permission Kes, judging by the monstrosity the council have allowed to be built out of the roof of the house to the right of your photo

You mean the 3-bed semi, with external insulation, 2-storey side extension, rear extension, loft conversion, and conservatory (recently added)? They're just filling in the corner between the side and rear extensions at the moment. They must have at least doubled the internal floor space (and lost most of the garden) but that's what some Asian families do near us. As the family expands, so does the house. Probably a good arrangement for childcare though!

Thanks again everyone.

 

[kdampney]

Further to the above, given that CLS actual dimensions seem to be so much smaller than 'nominal' sizes, should studwork be made from non-CLS timber?

e.g. a 2x4 CLS timber, nominal size 50 x 100mm becomes 38 x 89mm actual size - surely that makes fitting 100mm of insulation between studs a bit tricky?

How long can CLS (or non-CLS) timber and OSB2/3 be left exposed to the elements before it starts warping?

Thanks again

 

[RogerS]

I've had some OSB protecting some stone edging. It went down around last September and so far hasn't warped. However, I did have some spare Cuprinol lying around doing nothing and so sloshed a load of it on top.

 

[Wizard9999]

Further to the above, given that CLS actual dimensions seem to be so much smaller than 'nominal' sizes, should studwork be made from non-CLS timber?

e.g. a 2x4 CLS timber, nominal size 50 x 100mm becomes 38 x 89mm actual size - surely that makes fitting 100mm of insulation between studs a bit tricky?

How long can CLS (or non-CLS) timber and OSB2/3 be left exposed to the elements before it starts warping?

Thanks again

I used CLS and 100mm insulation. But it was the squishy stuff, not the rigid Celotex type so easy to compress as necessary, it might bulg a bit, but as long as the battens are a reasonable size there should still be a decent air gap between the outside of the breather membrane and the inside of the cladding.

Terry.

EDIT: tried to post these earlier, but Photobucket seemed to be down:

 

[kdampney]

Thanks Roger and Terry. I'll probably be using loft insulation for the walls, so that shouldn't be a problem.

I have seen some people saying CLS timber is great, and others saying its horrible stuff and there's no point using it compared to treated regularised timber... any thoughts?

 

[kdampney]

Also, as I'm losing my shed in this process, I need to have some garden tool (and paint tins, kids toys, other junk!) storage. If I have a separate external door for that, what are people's opinions on whether it should it be within the 'warm' insulated area (just a simple OSB wall between storage/workshop) or 'cold' non-insulated area (insulated OSB wall between the two)? Given there won't be heating in the storage area, I wasn't sure if condensation was likely (humidity from the wood and heated workshop.

It's also been suggested that I might want dust/chip extraction to dump to an outside bin to reduce the amount of fine dust getting back into the air (I know that might mean heat is dumped outside too). No need for that to be insulated, I just need to work out how to fit that into the scheme!

 

[Rod]

I used 100mm CLS and 100mm Rockwall insulation in the walls and ceiling without any problems on my shed build.
I also installed the membrane and cladding to make things weatherproof first then installed the insulation from the inside.
I also used EPDM for the roof - it's really easy to lay on top of OSB.

Rod

 

[Jimmy Mack]

Looking good Rod...Fast work!...I've got some catching up to do!

Keep up the good work and piccies.

Jim

 

[Rod]

Huhm - some pics from my shed rebuild project completed last Autumn [emoji3]

Rod

 

[kdampney]

Just trying to nail down some design details in my mind...

Does anyone have any photos or clear instructions (or even better, workshop-build threads!) on how double-glazed windows fit into timber framed walls please? Do they get screwed through the DG frame into the framework, before the glass is fitted? Do they sit directly in the studs, with trim/cladding securing the faces? How secure is that?

Also how does a ridge/rafter/bargeboard setup look if there is an overhang to the roof? What does the last set of rafters sit on - does the top plate extend out beyond the walls to support them? Or does the battens/sheathing just extend out with a barge board fixed to them?

Thanks

 

[Wizard9999]

Also how does a ridge/rafter/bargeboard setup look if there is an overhang to the roof? What does the last set of rafters sit on - does the top plate extend out beyond the walls to support them? Or does the battens/sheathing just extend out with a barge board fixed to them?

Thanks

If you mean hanging over the two ends then I think you need to do a quick internet search for "gable ladder" and all will be revealed.

Terry.

 

[kdampney]

If you mean hanging over the two ends then I think you need to do a quick internet search for "gable ladder" and all will be revealed. Terry

Aha, fantastic, thanks Terry