Insulating a flat roof

[Exfarmer]

Just building a conservatory with a fibre glass flat roof.
Rafters are 9x 2 ( 225 x 50 )
My builder wants to put 3 Kingspan on top then a n Actis hybrid mat underneath. This will then need a further 38 mm batten to hold it to the rafter before the plaster board.
I would sooner put 80mm Kingspan TR 26 on top and then afurther 75 mm packed between the rafters to give a U value about .13 before the plaster board is tacked to the rafter underneath. This would give me 38 mm hieght advantage and no problems with using downlighters.
Any one here with knowledge of such matters?

 

[Dry Rot]

Shouldn't we all be using sheeps' wool for insulation?? Yeah, I know!

 

[Exfarmer]

Shouldn't we all be using sheeps' wool for insulation?? Yeah, I know!

Great idea , but sadly not possible in this case

 

[br jones]

Just building a conservatory with a fibre glass flat roof.
Rafters are 9x 2 ( 225 x 50 )
My builder wants to put 3 Kingspan on top then a n Actis hybrid mat underneath. This will then need a further 38 mm batten to hold it to the rafter before the plaster board.
I would sooner put 80mm Kingspan TR 26 on top and then afurther 75 mm packed between the rafters to give a U value about .13 before the plaster board is tacked to the rafter underneath. This would give me 38 mm hieght advantage and no problems with using downlighters.
Any one here with knowledge of such matters?

Flat roofs are different to slopes.what do the regs say .i think that is to big an air gap

 

[How much]

condensation has to be considered we had some flat roofs done on some houses recently and I don't fully understand it but there are effectively hot roofs and cold roofs depending on if the insulation is above the joists or below , above is what we ended up with , with a vapour barrier inside the big advantage was the insulation had no breaks in it and was in in in two layers overlapping with taped joints and void was left for ceiling lighting etc .

 

[br jones]

Warm or cold roof? 150mm in between and 25mm underneath

 

[Exfarmer]

We have to be warm roof as we cannot ventilate it.
This is causing a lot of agro, as I want downlighting, but really do not want the membrane right tight over them. Nor do want the lowering of the ceiling