Insulating an outbuilding

[Adrian]

We've finally got a new roof on the studio building - corrugated metal sheet replacing asbestos cement. It's a reasonably large outbuilding, about 5m x 9m, and split into two rooms internally. The roof is currently plasterboarded on the inside of the slope, roughly 2.5m to eaves, 4m to apex. The walls are all block construction, and it probably dates back to the '60s. There's power and water, and a woodburning stove at one end.

The roof's insulated with the usual fluffy stuff, fairly well-packed but not absolutely rammed in. It's probably contemporary with the rest of the building. We'll be replacing the plasterboard currently forming the ceiling, probably with wood t'n'g. The new roof has four translucent sheets, full length from apex to eaves, for light.

So... what would you do to insulate it all? We'd like it to be fairly usable all year round, but won't be living in there.

The render on the front wall (south facing) needs patching, the others are still in scratch-coat, but we'd ruled out external cladding anyway, and now the roof's done, there's not really enough overlap. The walls on the inside need plenty of TLC, so everything's in play there. The woodburner's flue is fairly close to that wall - not much space to put anything behind it.

Budget is not unlimited, obviously.

[meow2222]

If you're not sleeping in there and escape's easy, expanded polystyrene is very cheap, easy to apply and works well. I wouldnt use it where people are sleeping though, its nasty stuff in a fire. Plasterboard over it will give plenty of time to escape in a fire before the plastic produces toxic gases .

NT

[Adrian]

My knee-jerk reaction is a "Thanks, no thanks" - there may be occasional sleeping-over in there, plus there's the woodburner in the "far room", with an internal door to the other room where the external door is.

[John Rumm]

I did my workshop (5.2 x 3.6m) with 50mm PIR foil faced foam boards, covered with 12mm shuttering ply. Simply screwed through the ply into the brick / block wall and used 5" screws and wall plugs. Did the slope of the roof as well (did not bother with the ply for that). It works well and can be kept warm easily. The PIR cost about £350 IIRC from a local supplier of "seconds" insulation boards.

[Tim Lamb]

In message , Adrian writes

Pity you can't go outside. Pallet of feather edge about £750.

75mm PIR seconds secured with 25mm softwood battens screwed to wall using plugs and adjustable screws. Finished with plasterboard or shuttering grade ply.

[JimK]

Nah just fo screws like John did & ditch the battening & void creating hassles.

Jim K

[RJH]

What method did you use to mate the 5" screws and wall plugs?

[Tim Lamb]

In message , JimK writes

An alternative put forward by TNP was to use horizontal 75mmx50mm and infill with PIR foam.

Would give stronger fixing points for shelving etc.

[JimK]

Screwdriver?

Drill hole, put plug in hole, insert screw, tap with hammer til home, turn with screwdriver?

Jim K

[Tim Lamb]

In message , JimK writes

Alt. Carbide tipped drill through batten, PIR and into wall. Start plastic plug on end of screw. Push home and tighten screw with impact driver, drill, what have you. Adjustable screws have star heads so not suitable for hand tightening.

[RJH]

Bit tricky to ask as you snipped the context - drill through the 60mm, then? Bearing in mind these are 6'x4' sheets, I'm just curious as to the best method to match up the hole in the wall with the hole in board.

I'd drill through the in-place board, score the wall, remove the board, drill and plug the wall, refit the board and hope it all lined up. Hoped ;-)

[RJH]

Wouldn't the hole required to push the plug through the board be too big? I don't think battens were used in the snipped example.

[Tim Lamb]

Depends on the plug. You don't want the ones with a shoulder:-)

I've got some left over adjustable screws if you want to practise:-)

There is another way, unmentioned as yet.... You can buy PIR foam sheet with a plasterboard finish. Dot and dab to your blocks. I have never used them because of the difficulty in securing shelving etc.

Have a dig in the Kingspan site.

>

[John Rumm]

a 6" long 7mm Bosch multimaterial drill bit - offer insulation and ply up against the wall, drill through the lot and about 2" into the wall with the drill. Twist plug onto end of screw and offer into hole, tape home with hammer until the plug is seated in the wall, and only 2" or so of screew remains protruding, and then drive that home. Used 6 fixings per 8x4' board.

[JimK]

Wot I said (& John detailed further)

Jim K

[RJH]

Well, er, yes! Just thought that with the softness of the material you'd want as little wiggle as possible.

You're very kind :-)

Yes - familiar with it. Alas when I did a similar project I had plain foil backed insulation board, and faced it with a separate sheet of plasterboard. In the end I screwed it into battens. I'd rather have simply screwed it into the wall, but couldn't work out the best method.

In the event the small cavity has proved useful to route some wiring I've now decided I need.

[RJH]

Ah, gotcha, thanks. I had thought of that, and have some slimish plugs - but they were uncomfortably close to the diameter of the screw head. My case was fixing to plasterboard - a lot softer obviously than your ply. And I was concerned about the 'wiggle' between board and screw.

But thinking about it the load (that matters) is really compression, against the wall, rather than holding anything up. I'll know for next time!

[Adrian]

She's just discovered "Expanded cork board" - and is thinking it could be good, left unfinished.

Anybody used this stuff or similar before?

[meow2222]

bit steep. Cork was once a fashionable insulator, but there are cheaper better performers now.

NT

[John Rumm]

and more cold bridges and hassle etc.

I find for most normal fixing, screwing to the ply is more than adequate (remember its sitting on the floor - all the screw are doing is stopping it pulling away from the wall).

For heavier loads I just use long screws and repeat the ply fixing trick bu screwing into a plug in the blockwork.