Loft insulation thickness

Hi all.
I cleared out all of the old insulation a few months ago.
And I suppose I should replace it but not sure what
thickness of stuff to use.
I also need to lay a few sq metres of loft flooring.
The ceiling joists in my loft are 3" deep so what thickness
of insulation should I choose?
I think I'm just concerned that if I lay insulation more than 100mm
thick it will prevent the floor panels from sitting down.
The whole arrangement is a temporary arrangement as I plan to
convert the loft into a bedroom.
Reply to
You can lay 100mm between the ceiling rafters and when you lay the flooring the insulation will simply compress down - assuming that it is of the simple fibreglass wool type of material.
Now with regards to converting the loft to a bedroom, remember that 3" ceiling rafters are not designed to carry any heavy loading and you will need to install floor joists to at least 7" x 2" (depending upon their length you may have to go 'bigger').
Reply to
Brian G
Dear Arthur If it is temporary, I would not bother to use rockwool or fibreglass as Building regs and commonsense require some 300 mm odd depth now I would purchase (as cheaply as poss - seconds?) TP10 or the like from Kingspan and lay that in between the 3" joists where you want to use it as temp flooring (put acrows in down below to support) and lay the rest in large slabs over the joists ready for cutting up when you do your complete conversion later as the TP10 will have to be 150mm thick in rafters and that means 3" in between (to allow 1" ventilation and 3" inside the line of the rafters to get a decent U value. Chris
Reply to
I would stick with 100mm under the boards for the moment. This won't be wasted as it can be relaid between the larger joists later to improve fire transmission resistance.
If you want more than that, then divert your attention to insulating the slope of the roof since this will also be necessary once you convert the space. Foiled PIR foam panels being the material of choice for this.
Reply to
John Rumm

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