Dry-lining a shed

[Andy Dingley]

The shed refit progresses...

I'm now trying to decide what to do with the inside walls. They're single cement block, cold and damp. Plan is to insulate on the inside with 1" white polystyrene, then dry-line with plasterboard over that. Original blocklaying is somewhat uneven, but the polystyrene will cope with that.

Question is, how to fix it? I'm not keen on dot&dab / tube mastic, especially as it's over fragile insulation, so it looks like I'm going to have to batten the walls out first, then drywall screws into that.

What spacing should I use for the vertical battens (and this is a shed workshop)? 600mm between battens to fit the insulation, then board out the plasterboard butted over this (with the resulting uneven screw locations)? Or trim each insulation board down to a batten's width less than the plasterboard? I'm not battening top & bottom. What size battens should I use? 1" x 1"?

Or is there any easier way?

Floor is solid concrete(sic) with a couple of inches fall from one end to the other. Over this I'm laying the grey foam "high performance" thin floor insulation (allegedly sufficient moisture barrier) and then

18mm OSB2. Plan currently is to lay this between the plasterboard, rather than beneath it.

Thanks for any advice

[Pete Verdon]

Is that not likely to allow damp into the bottom edge of the plasterboard?

Pete

[dent]

The plasterboard needs to be properly supported along the edges, so lay the battens to match the plasterboard widths, and then cut the insulation to suit. Some insulation batts are sold `to fit 600mm spacing', meaning that they are actually undersized to start with to deal with this exact situation.

I would probably put a horizontal batten in at centre height as well to provide a bit more support.

At least as deep as the insulation. 1" width is okay for the battens inside the board, but for the edges you want to go a bit wider. The screws shouldn't be closer than 10mm or so to the edge, so if two bits of plasterboard butt up against each other, then the batten needs to be 20mm wide to accommodate the screw spacing, plus enough extra for the screw to bite into.

Not easier, but using ply/osb may be more durable. I did my workshop in plasterboard, and it it constantly getting dinged by timber falling against it, and so on.

Might be useful to run some conduit for sockets at the batten stage.

dan.

[Bob Minchin]

Andy, I've not been following this project to date but are the block walls you are going to dry line outside walls if so you will need to waterproof them first.

My workshop is single skin blockwork and I sprayed it with synthaprufe bitumen emulsion, then battens, then dust sheet polythene (to stop the bitumen attacking the polystyrene, then 25mm polystyrene then 18mm plywood painted with cheep emulsion. I used tiling battens which are pressure treated on 400mm spacing as I was planning to hang wall cupboards on the ply but 600 would be OK if you don't mind a bit of a wavy surface.

Bob

[mark]

You can get plasterboard with 25mm insulation stuck on the back. This is screwed on to your 2" x 1" battens Consider also fixing horizontal battens at appropriate heights to receive wall cupboards etc.

mark

[JimK]

indeed - especially as polystyrene is permeable....

it's a workout the costs jobby :-

a dryline with another "closed cell" foam (=A3=A3=A3s) that won;t allow vapour to permeate?

b could foam-back plasterboards =A3=A3=A3s be dot and dabbed straight on or is it "wringing" wet? this would save space, be quick to do, more insulation than polystyrene would givee per mm.

c or do the bitumen thing (wickes do their own in various big tins)

d someat else?

cheers JimK

[John Rumm]

I did mine with ply lining and no battens at all. Just used long screws through the ply and insulation and into the wall. Saves any cold bridges, quicker to do, and the ply is much simpler to fix stuff to later.

[Jim]

...apart from the screws. Can you get thermally broken screws?

I'm only joking, really, it's just that you reminded me of the discussion I saw on the greenbuilding forum about thermally broken wall ties.

[John Rumm]

Daft as it sounds, you can of sorts... I have been looking at how to insulate the outside of my house (solid wall), and one of the fixings commonly used seems to be a primarily nylon plug and pin arrangement so as to have no bridging effect.

Got to be into the land of diminishing returns by the time you get that obsessive!

[Andy Dingley]

Hopefully not. The floor ends up about an inch above slab level, so I'm planning on lifting the plasterboard edges slightly above this.

I'm also considering installing skirting boards, because otherwise the plasterboard will get smashed at the bottom edge whether it's on a batten or not. This shed (24' x 8') is going to be used as small workshop, bike store and lawnmower store, so there will be some banging and crashing around in there.

[Andy Dingley]

Thermal bridges just aren't an issue. It's going to be mostly unheated, with intermittent use. That's one reason I'm putting the insulation on the inside, not the outside.

[John Rumm]

When I did mine, the lack of thermal bridges was an advantage rather than a reason for doing it that way. The reason for doing it the way I did was ease of application and cost really. I used 50mm PIR foil faced foam, stuck some dabs of expanding foam on it, and slapped it against the walls. Filled any voids and gaps round the insulation with foam. Then the ply over (12mm WBP shuttering ply stood vertically), and typically 6 screws per sheet. Finally filled the gaps in the ply with decorators caulk and gave it a coat of magnolia emulsion. For the roof pitch I insulated under the rafters (there was already eves ventilation), but have not bother covering the insulation on that as yet

- just left it silver to help bound the light about a bit more.

All in all it made it a nice place to work, much easier to heat and keep dry, lighter, and better sound damping. I toyed with using plasterboard to start with, but I am glad I went with the ply in the end. It makes it easy to hang stuff, and it won't go soggy if any damp gets into it. Big shelves I stuck on long spur style uprights, so most of the load is on the ply in shear. The only thing I have not done yet is the floor. That is still a concrete slab.

I may stick a thermostatically controlled fan heater in there at some point, just to provide an lower limit and control damp. I will also get a reclaimed DG window for it at some point.

[NT]

I wouldnt go with PB on battens, its too weak. But if you do, make sure the battens at the edges of the PB are 2" wide, when you get down to 1.5" the fixings are so close to the edge the pb sheets become weak.

Battens that dont support PB edges can be any old junk, including assorted scrap offcuts stuck on the wall.

NT

[robgraham]

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I go with John - PB seems an unwise solution, if for no other reason than you cannot hang things off it reliably. I used OSB board but perhaps in hindsight I should have looked at shuttering ply.

Mine is a wooden framed workshop and I had the time to go as cheap as possible and I used fibreglass insulation, but it was time consuming to staple into place.

Rob

[David WE Roberts]

Very useful information - I am about to start on my shed project and all this is really good to know.

One thing - you stuck the foam to the wall, then screwed the ply to the foam?

Or did you drill through into the wall and use frame fixings?

I am a bit of difficulty picturing ply held up by 50mm foam with other things then hanging on the ply.

Cheers

Dave R

[David WE Roberts]

Sigh. One day I will learn to read :-(

So the question now is - did you plug the walls, use frame fixings, or what to fix the screws into the walls?

Please ignore previous post!

Cheers

Dave R

[John Rumm]

I used foam to stick some bits - as it was easier to do some bits of foam fettling before worrying about the ply. When doing the big open spaces the foam did not really need sticking as such.

I used 5 & 1/4" No 12 twinthread screws, into a brown plug. Using a 7mm x 160mm long multimaterial bit in the drill, its easy to drill straight through the ply, insulation, and a couple of inches into the blocks beneath. Wind a screw a couple of turns into a plug by hand, poke the end into the hole in the ply, and then hammer in until only a couple of inches remain sticking out. Give that bit sticking out a whizz with the screwdriver/impact driver until it has pulled itself flush with the ply (or preferably a little countersunk).

;-)

[Andy Dingley]

I'm certainly not going to be hanging anything off the plasterboard - I'll be drilling into the cement blocks. It's only an inch deeper.

Electrics will be plastic conduit on the surface, maybe even across the (exposed) joists.

I'm still not sure what this workshop is for anyway, which makes design difficult. It was originally planned to be for foundrywork, smithing and steel fabrication (dirt-chucking mangle grinders), to keep fire out of the other shed full of woodwork. However the roof was rubbish and needed replacement, which has spiralled into a full insulation job. As there's a chance I might actually finish it (the big shed is taking FOREVER) it would be nice to rig it up for jewellery making in the meantime. It wouldn't hurt to put the small lathe in here. Whether it stays that way, quite another question.

[Cicero]

================================================

Since this shed is likely to see further unspecified changes it might not be necessary to *attach* anything to the walls. Fasten insulation to your plywood (use special plastic 'screws')and attach vertical battens to the inside face edges. Screw through the battens on adjacent panels or screw a wider facing covering as connector. Attach your skirting direct to the floor, positioned to hold the panels close to the walls. Add a few horizontal stretchers at the top of the panels and the job's done - a shed within a shed.

Cic.

[js.b1]

B&Q do Knauf extruded polystyrene sheets at the moment.

I recall they are 1200x500/600mm, 50mm thickness, pack of 5, =A319.95. Extuded polystyrene is waterproof unlike "conventional" expanded polystyrene.

They are sold to line lofts with where people want storage. The packet also said suitable for lining sheds etc.

A pity Marmox isn't subsidised in the same way: 50mm costs =A3100+ for extruded polystyrene with a bit of cement & glass fibre mesh on each side. Marmox is very handy for keraflex wall, stick on marmox, skim over. I do not like batons on solid walls, too easy for the dew point to moves out of the wall into the void.