Workshop Roof Internal Insulation

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Dynamite

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Hi all, i was after knowing what you all think about my shop roof plans. It’s a standard garage sized workshop with traditional apex joisted roof. It has a new roof, tiles, soffits, gutters etc done in last couple of years. As you can see, there’s just a membrane between the tile and the shop. I would have got them to felt it but wasn’t planning it being a space I would use as a shop at the time. Nevertheless, it is what it is.

The tile to bottom of the joist is 100mm so I was going to leave 50mm air gap from the tile then put 50mm kingspan insulation then board over with pallet wood rather than plasterboard or sheet wood to save a bit of cost as i have pallet wood already.

Photos below, what do you think?

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IMG_6988.jpeg
IMG_6987.jpeg
 
As you can see, there’s just a membrane between the tile and the shop. I would have got them to felt it...

The membrane will be better than any felt that could have been used.

What does the pallet wood overboarding add? Other than being a bit surdier than Kingspan if you like prodding things into the roof?

To me, it just reduces headroom and offers no benefit. If you have the space to put pallet wood there, put 50mm insulation between the rafters and then 25mm insulation where the pallet wood might have gone. That gives you 50% extra insulation thickness for minimal loss of space.
 
The membrane will be better than any felt that could have been used.

What does the pallet wood overboarding add? Other than being a bit surdier than Kingspan if you like prodding things into the roof?

To me, it just reduces headroom and offers no benefit. If you have the space to put pallet wood there, put 50mm insulation between the rafters and then 25mm insulation where the pallet wood might have gone. That gives you 50% extra insulation thickness for minimal loss of space.
Wood is a pretty good insulator! And allows you to attach things to the ceiling...
 
Careful with the weight covering the insulation with pallet wood will increase the loads on the roof by quite a bit.
 
Why not just use insulation, ie Kingspan or Celotex between joists, either pinned in or expanding foam ( best option IMHO),, then staple thermal insulation foil over that.
 
If the membrane is breathable then skip the air gap and use insulation to the full depth. Insulation effectiveness is considerably reduced by gaps, so think about how well you can fit the Kingspan, Gapotape can help a lot. If your membrane is breathable then I'd go for a 100mm thick rockwool batten, as it will conform to the joist shapes much better!

The main thing you get worried about when insulating is condensation on the cold side of the insulation. This is why you leave an airgap if the cold side is not breathable, such that condensation can evaporate. Batten wood has lots of gaps so I'd suggest you put a vapor barrier over the insulation before you put up the batten wood. However, this is a shed not a house or bathroom, so I expect it'll be cooler and less occupied so interstitial condensation is likely less of a concern.
 
i have used celotex, if unsupported behind with battens and held in at the front face it distorts or bows some 50mm over 1250mm,that was 100mm thick, after a period of time, in my case 2or 3 years. other makes no problem
 
i have used celotex, if unsupported behind with battens and held in at the front face it distorts or bows some 50mm over 1250mm,that was 100mm thick, after a period of time, in my case 2or 3 years. other makes no problem
Thanks for the heads up. I will put battens behind anyway, whichever product choose if I do go ahead with this.
 

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