# Ceiling for workshop



## ObservantGround28 (28 Apr 2020)

I wanted to cover the exposed joists in my workshop by insulating with 10mm of Polystyrene and the covering it with 3.2mm of plywood.

Anything wrong with my thinking? The joists are on 16” centres, will the proposed ceiling sag? 

Thanks


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## fezman (28 Apr 2020)

I've just done something similar, but as I am on my own for things like this i decided fixing large sheets of ply would be a PITA.SO I went with 8mm T&G internal cladding. My garage workshop was very drafty, and fixing these up and putting some rockwool type insulation has made a huge difference to both the temp and the noise dampening. I used the cladding from wickes and it was ok for this type of work.


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## Steve Maskery (28 Apr 2020)

ObservantGround28":3qjkhzum said:


> I wanted to cover the exposed joists in my workshop by insulating with 10mm of Polystyrene and the covering it with 3.2mm of plywood.



Personally I think that 10mm of polystyrene will have virtually no effect whatsoever.


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## That would work (28 Apr 2020)

Why 10mm thick insulation? That won't do much? Would you not want to go as thick as your joists? (With any allowance for ventilation under the roof covering).
I would use 11mm osb for the ceiling, cut the sheets up into convenient pieces. Those centers are fine, you could add some trimmers if they will make fixing the ceiling easier.


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## MikeG. (28 Apr 2020)

ObservantGround28":3t8oz5li said:


> I wanted to cover the exposed joists in my workshop by insulating with 10mm of Polystyrene and the covering it with 3.2mm of plywood.
> 
> Anything wrong with my thinking? The joists are on 16” centres, will the proposed ceiling sag?
> 
> Thanks



Yep, don't even think about doing this. Polystyrene turns into napalm in a fire and gives off a lethal gas, so should never be used in a buildings construction unless buried behind or under something completely fireproof, such as screed. 10mm is completely pointless anyway. That hasn't got the insulating properties of even an inch of fibreglass/ mineral wool.


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## DBT85 (28 Apr 2020)

If the joists are exposed why only cover them and not fill in between? Seconds (not full sheets, usually from jobs that have too much or its "faulty" pir foam or rock wool would both be fine and do well.

If you really just want to cover it rather than fill the gap, at least use some 25mm pir sheet. Not that it will make that much difference I wouldn't imagine.


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## ObservantGround28 (1 May 2020)

I should have and forgot to mention that I have installed 100mm of PIR boards in between the joists. When we had the extension done, an "error" was made and they had to redo the wall insulation. As a result I had a lot of the 100mm PIR foam in various sizes left over, I've only managed about 1/3-1/2 of the ceiling with complete boards and the rest made up of pieces which was a PITA. I'm going to foam the gaps - not looking forward to that.

My thought on the 10mm was really around an extra layer of thermal decoupling between the finished ceiling and the joists. 

So basically, I'm understanding that everyone is saying that doing this is a) pointless and b) dangerous in the event of fire when used internally. Thanks for the advice.

Moving on from that, what would be a suggested covering? I'm on my own so 8x4's of anything is going to be "fun" (unless I get hold of a suitable sheet lifter). 

Thanks again all.


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## DBT85 (1 May 2020)

Ahh well that changes things substantially! haha.

The foam won't be too bad. Don't go mad with it and for christ sake don't touch it till its dry.

I'd either use some 25mm PIR and then some boards or just some boards. When I do mine I'll just board it with insulation in between the rafters.

Plasterboard or just 11mm OSB would be fine. Could always cut them in half to make lifting easier if you can't borrow a lifter.


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## Inspector (1 May 2020)

When my house was being built covering the walls and ceilings in the workshop was my responsibility. Putting the OSB on the walls was easy but doing the vaulted ceiling alone was not something I was looking for ward to. I asked the drywall boarding crew boss how much he would want to put the 26 or so OSB sheets up on the vaulted ceiling. He said $250 cash and I said yup. He and the 2 other guys came in on a Saturday morning and had them all up in a little over two hours. It would have cost me more to rent a lift for a few days to do it myself and I didn't do in my back. Look into getting some guys to do it.

Pete


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## DBT85 (1 May 2020)

Brandon tools will hire you a lifter for £75 for a whole week. Doubt you'd need it a day.


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## ObservantGround28 (1 May 2020)

DBT85":2xfsf87v said:


> Brandon tools will hire you a lifter for £75 for a whole week. Doubt you'd need it a day.


Googled "HSS lifter" and came across "Hire Services Southern" rather than the expected "HSS Hire". They rent them out for £35 for the week (ex del)! They're pretty local so I'll call them up to see if it's still a good deal with delivery charges.

I'll rope in an extra bod or 2 when things are less socially distanced and pay them with beer, pulled pork and brisket.

Thanks again all and stay safe.


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## Heliotrobe (2 May 2020)

ObservantGround28":3uwki386 said:


> I should have and forgot to mention that I have installed 100mm of PIR boards in between the joists. When we had the extension done, an "error" was made and they had to redo the wall insulation. As a result I had a lot of the 100mm PIR foam in various sizes left over, I've only managed about 1/3-1/2 of the ceiling with complete boards and the rest made up of pieces which was a PITA. I'm going to foam the gaps - not looking forward to that.
> 
> My thought on the 10mm was really around an extra layer of thermal decoupling between the finished ceiling and the joists.
> 
> ...



If I may offer a piece of advice based on having been in the same boat as yourself. If you can, borrow or buy a foam gun from Screwfix or the like. Way more controllable and less wasteful. 

Regards

Heliotrobe


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## ObservantGround28 (2 May 2020)

Thanks Heliotrobe,

Luckily I bought one earlier this year when I was doing some other work.


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## The Bear (2 May 2020)

I use hire services southern regularly as my mate has an account. Very helpful guys. Not sure whether they deliver up to you but if not try Dual tools in Worcester park another good independent up your way
Mark


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