Fixing Kingspan with Expanding foam?

[leew2]

Hi, building a new garage and I am at the stage of adding the roof. I am thinking of using 100mm Kingspan between the joists of the flat roof. I insulated by existing garage with kingspan by carefully cutting pieces to the exact width between the joists and even then there were some gaps. This was very time consuming, made worse as none of the joist spacings were the same and some were not even parallel. I was wondering it would be easier to cut the boards slightly smaller, say 10mm all round then fill the gap with expanding foam filler. Will that work and the filler not react with or damage the kingspan?
The reason I want so much insulation is because I will being using it for composites work occasionally which will mean I need to maintain it at 20-25c.

Also do I need a vapour barrier? Roof will be fibreglass over OSB3 decking then 50mm air gap ventilated at eves then 100mm kingspan then 9.5mm plasterboard ceiling.

Many thanks.

 

[freddiemercurystwin]

Also do I need a vapour barrier? Roof will be fibreglass over OSB3 decking then 50mm air gap ventilated at eves then 100mm kingspan then 9.5mm plasterboard ceiling.

Use foil backed plasterbaord for your Vapour Barrier. Ply would be better for the roof although more expensive.

BTW even though you are not building to the regs 100mm Kingspan would not meet the regs nowadays so not really overkill. Maybe consider upping it some more, you'll only spend more on heating if you need to maintain that temp for long periods.

Also I recall 9.5mm boards are recomended for a maximum joist centres of 450mm even then it may sag so if more than that go for 12.5mm boards.

 

[ajrobb]

How much height do you have?

I think there are options:

• 'warm roof' insulation over non-vented timbers
  'cold roof' insulation under vented timber
  insulation between timbers with 50mm ventilated gap above

If building regs call for 250mm of mineral wool, that is equivalent to 150mm of PIR (Celotex/Kingspan). However, the difference between heat lost though 100mm and 150mm of Celotex is minimal and probably a waste of money.

It might be easier to fit insulated plasterboard under the joists. If you have wiring above, you probably should avoid polystyrene insulation (it degrades PVC electrical insulation) and go for something like Kingspan K18.

Another alternative is to fix Celotex below joists with battens. You then have the choice of fitting plasterboard or using the foil surface to reflect work light.

Have a look at http://www.british-gypsum.com/liter...ing___soffit_systems/sb_timber_joist_pdf.aspx

 

[leew2]

I am building it without planning permission, which means to stay within PD, I need to keep the overall height under 2.5m. I want as much ceiling height as possible which is why I want to place the insulation between the joists rather than above or below despite the extra difficulty fitting it and thermal bridging though the joists. I was thinking of using 20x20mm battons on the sides of the joist and sitting the plasterboard and kindspan ontop. This means the bottoms of the joists will be exposed making it easy to put hooks etc into them to hang things up.

 

[ajrobb]

If you are going to expose the joists, why bother with plasterboard? You could fix Celotex between the joists using Celotex Insulation Clips nailed to the bottom of the joists.

 

[geraldthehamster]

Hi, building a new garage and I am at the stage of adding the roof. I am thinking of using 100mm Kingspan between the joists of the flat roof. I insulated by existing garage with kingspan by carefully cutting pieces to the exact width between the joists and even then there were some gaps. This was very time consuming, made worse as none of the joist spacings were the same and some were not even parallel. I was wondering it would be easier to cut the boards slightly smaller, say 10mm all round then fill the gap with expanding foam filler. Will that work and the filler not react with or damage the kingspan?
The reason I want so much insulation is because I will being using it for composites work occasionally which will mean I need to maintain it at 20-25c.

Many thanks.

Answering your specific question, yes, you can fix it with expanding foam, and it will be fixed firmly with no gaps. I've done this several times, in a stud wall, in a sloping roof, and between joists in a suspended floor. It won't react with the kingspan because it's the same stuff.

Cheers
Richard