Can someone advise us please. We are building an extension to our kitchen , it will have a flat roof witch will be felted. What insulation should we put between the joists and what thickness? to comply with latest requlations.Thanks.
ceiling insulation to new flat roof
- Thread starter nalle59
- Start date
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it is less fuss to insulate over the joists as opposed to between.
kingspan sell an insulated plywood sheet specifically for this purpose and the required thickness is 97mm.
recently, we were required by b.c. to install a further 25mm between the joists.
you can full fill with kingspan or celotex or partial fill which would require venting.
kingspan sell an insulated plywood sheet specifically for this purpose and the required thickness is 97mm.
recently, we were required by b.c. to install a further 25mm between the joists.
you can full fill with kingspan or celotex or partial fill which would require venting.
oops edited. 
Thanks for your reply ,putting kingspan on top of joists will lower the ceiling somewhat ,does one blasterboard it after? we have an RSJ to box in as well which support the roof , we were hoping to fill the joists with something suitable with air cap of 25mm on top
.The new extension joins on older flatroof extension which we filled with rockwool to required depth and then blasterboarded the ceiling , the front facia has ventilation in the front and under, it is upvc ,we will use this to match our new extension.
The carpenter says that he will use some fireretardant board to box the RSJ in but has not idea what insulation to put between the joists to meet the regulations.
The floor will be concrete with 95mm celotex insulation.
Any more ideas to what we shoud do?
.The new extension joins on older flatroof extension which we filled with rockwool to required depth and then blasterboarded the ceiling , the front facia has ventilation in the front and under, it is upvc ,we will use this to match our new extension.
The carpenter says that he will use some fireretardant board to box the RSJ in but has not idea what insulation to put between the joists to meet the regulations.
The floor will be concrete with 95mm celotex insulation.
Any more ideas to what we shoud do?
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the kingspan plywood sheet sits ON TOP of the joists not below, in other words, it is your roof deck and insulation board rolled into one.
you simply apply the felt covering directly over the plywood top.
simply filling with fibreglass may not satisfy current reg's. if the joists are less than 270mm deep then you will not achieve the required spec. plus, cross ventilation would be needed providing ventilation at BOTH ends of the joist run. if this can not be provided then a series of mushroom vents will be needed.
you simply apply the felt covering directly over the plywood top.
simply filling with fibreglass may not satisfy current reg's. if the joists are less than 270mm deep then you will not achieve the required spec. plus, cross ventilation would be needed providing ventilation at BOTH ends of the joist run. if this can not be provided then a series of mushroom vents will be needed.
how deep are the joists?
We also do not know what insulation the bricklayer is to insert to the brick /block cavity , a builder said rockwool , it is a very small amount of brick/block work 730mm wide 2600 high on either side of the french doors and a small amount on the side.
The whole extension is only 2m deep by 4.50m wide .
Thanks for your help.
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