Office Shed build: shed is up but what next?

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rich1983

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I had a shed built a couple of years ago (12x12) and I put a bugger load of celotex type insulation in and then boarded over it. Depth of cavity between timbers is 70mm for walls and 150mm for ceiling.

I had huge problems with damp and condensation and was told that I should have done the following (in order from the actual wooden wall)...

- 10mm batton strips to make an air gap behind the insulation.
- breathable membrane (over batton?)
- 60mm celotex (or similar)
- plasterboard

- similar for ceiling but circa 140mm insulation? Would I need to membrane the ceiling considering the roof (sealed felt) isn't breathable anyhow?

Does this sound correct? I was told that my damp problems were probably due to the fact that the shed walls would become damp and perhaps let a little moisture in which wasn't then escaping as there was no cavity. I have been told that the batton coupled with the membrane will allow any moisture that gets in the shed to evaporate outwards, as opposed to going to the highest point in he shed roof (being the front wall and ceiling as it's just a pitched roof running down to the back gutters).

I don't want to bugger this up again and have to shell out for all the kit again. To be honest tho only some of the plasterboard was buggered (but I checked it all) and the insulation I had was given to me from Freecycle. It was 100mm depth and I had to cut it down the middle (one of the shittiest jobs I have had to do) but will just buy some proper stuff this time to make sure it's all good.

Can anyone give me any further tips or advice? I'm literally back to the woodeb boards now.
Office Shed build: shed is up but what next?
Office Shed build: shed is up but what next?


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rich1983 said:
I had a shed built a couple of years ago (12x12) and I put a bugger load of celotex type insulation in and then boarded over it. Depth of cavity between timbers is 70mm for walls and 150mm for ceiling.

I had huge problems with damp and condensation and was told that I should have done the following (in order from the actual wooden wall)...

- 10mm batton strips to make an air gap behind the insulation.
- breathable membrane (over batton?)
- 60mm celotex (or similar)
- plasterboard

- similar for ceiling but circa 140mm insulation? Would I need to membrane the ceiling considering the roof (sealed felt) isn't breathable anyhow?

Does this sound correct? I was told that my damp problems were probably due to the fact that the shed walls would become damp and perhaps let a little moisture in which wasn't then escaping as there was no cavity. I have been told that the batton coupled with the membrane will allow any moisture that gets in the shed to evaporate outwards, as opposed to going to the highest point in he shed roof (being the front wall and ceiling as it's just a pitched roof running down to the back gutters).

I don't want to bugger this up again and have to shell out for all the kit again. To be honest tho only some of the plasterboard was buggered (but I checked it all) and the insulation I had was given to me from Freecycle. It was 100mm depth and I had to cut it down the middle (one of the shittiest jobs I have had to do) but will just buy some proper stuff this time to make sure it's all good.

Can anyone give me any further tips or advice? I'm literally back to the woodeb boards now.
Office Shed build: shed is up but what next?
Office Shed build: shed is up but what next?


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What insulation are you using?
 
That's what I'm aiming for with regards to internal finish. Did the list I put up (the order of things etc) miss anything other than polyurethane?

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It had 50mm celotex flush with the timber on ceiling with 6inch square gaps for down lights. 50mm celotex flush with timber inside then polythene walls with 8in overhang stapled to the ceiling. Run cable for sockets on top of wall joist then cut plasterboad strips to pack out to cover cable and then board on top. I chose to tape and joint with paper tape because i was worried about skim cracking. Those photos were taken tonight, it's 18 month's old now.
 
Sorry Mr theshed, but I don't quite follow...

Should I use the membrane as I described? Plus the polythene you suggested?

I was going to put the electrical cable horizontally through the frame, drilling through the uprights to cater for it. Same for the ceiling, was just going to drill through the beams for the ceiling light cable.

Also you didn't skim: just tape and fill and then painted?

Finally did you do anything for ventilation
? I see there are loads of double glazed windows in that she'd. Did they have vents in? I was thinking about putting a small square vent in front and back to create a draft to keep moisture down, especially if I end up sealing it up (fill and tape or skim).



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Just put the membrane under the plasterboad on the walls. By running the cable on top of the wall joust, polythene over the top and then plasteroard the joist gives you enough room to fit plastic drywall boxes for sockets. My mate used second hand double glazed windows £30 each and second hand door off of ebay. I would never polythene the ceiling.
 
You don't need the battons just celotex across and board straight on top. You could vent each bit with a couple of holes if you wanted. Forget the polythene the celotex does that job, aslong as there are no leaks it should be fine, maybe get a hose on it just to check? What you doing with the floor?
 
rich1983 said:
Celotex board type stuff I figured maybe polystyrene but celotex appears to be about 20% more effective.

Do you have any suggestions?

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I'd go with the polystyrene slabs.

The wood breathes so you won't get any condensation and unless you have heating, you aren't really insulating anything because there's no heat to keep in. You're just keeping the wind out.
 
Sorry for absence of responses...

Floor is already polystyrene between the timbers. No membrane. This was installed as part of the shed order.

RE insulation and heating: I will be hearing the shed with electronic blower or oil filled radiator or a halogen but it won't be gas powered or anything like that. I want to use it in the winter and last winter it was bloody freezing with no insulation.

Thanks very much for all your posts and tips guys.

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rich1983 said:
Sorry for absence of responses...

Floor is already polystyrene between the timbers. No membrane. This was installed as part of the shed order.

RE insulation and heating: I will be hearing the shed with electronic blower or oil filled radiator or a halogen but it won't be gas powered or anything like that. I want to use it in the winter and last winter it was bloody freezing with no insulation.

Thanks very much for all your posts and tips guys.

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We use electric radiators from a maker called haverland they are great...

Halogen heaters are not really ideal in my opinion it would be like being in a massive toaster :-)

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I'll defo do breathable. I'm not sure if the current felt is breathable...

I'm not entirely sure what sort of heater I'll use (presently got a small electric blower thing) by point was more to get feedback on such types, particularly if any is more prone to causing moisture.

RE a loft conversion: Do you mean the sarking felt needs to be breathable as most loft conversions are tiled, obviously.

At this point I'm skint so it's all on hold but with all the tips I've received I will be more confident that I'll not have any problems. I did however discover that you can buy surplus celotex and similar which are reclaimed when a job over orders which should suit me fine.

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rich1983 said:
I'll defo do breathable. I'm not sure if the current felt is breathable...

I'm not entirely sure what sort of heater I'll use (presently got a small electric blower thing) by point was more to get feedback on such types, particularly if any is more prone to causing moisture.

RE a loft conversion: Do you mean the sarking felt needs to be breathable as most loft conversions are tiled, obviously.

At this point I'm skint so it's all on hold but with all the tips I've received I will be more confident that I'll not have any problems. I did however discover that you can buy surplus celotex and similar which are reclaimed when a job over orders which should suit me fine.

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the roofers have not used felt on roofs for years. it is all Tyvac a breathable membrane. polythene was never used on timber framed housing. it was for years vapour barrier plasterboard now Tyvac.
 
Tyvac in place of sarking felt yeah? Doesn't so much apply to the shed build as it's got roofing felt which i figure is different?

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rich1983 said:
Polythene between the plasterboard and celotex or the shed walls and celotex?

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breathable felt is a waste of time in a shed especially if you are cutting the insulation tight between the battens. It would be appropriate for a tiled roof where there is an allowance for air movement but the shed roof above the insulation will effectively be sealed. You should put a small ventilation gap a either end (I use 25mm air gaps usually). The insulation itself is sufficient to form a vapour barrier assuming its foil backed. If you do put a membrane in I would use 1200gauge polythene and put it on the inside of the insulation before the plasterboard. This will also improve heat retention very considerably. I would also get the filler gun out and fill the gaps between the board where you can see daylight in the pics.... A vent in the door would not go amis either as its a shed when all is said and done and will trap moist air which overnight in cold weather will condense. IN terms of heater use electric or infra red. Don't use anything that burns fossil fuels as this produces moisture itself.
 
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