Loft flooring/Insulation - Condensation issues

[andrew5235]

Hello,

I would like to floor my loft, I already have loft insulation in place. The problem is that the loft insulation sits about approx 3'' above the 5'' joists. Is it OK just to floor over this and squash it down or will this lead to condensation problems? I will not be flooring the full width of the loft, probably about 65 - 75% of the width

I will plasterboard about half of the loft walls and ceiling but there will be at least 3 or 4 feet all the wall around it for ventilation. Just concerned about the floor.

Should I go for a thinner loft insulation, put a vapour barrier below the existing loft insulation, use rockwool slabs, which I believe are thinner but just as insulating, or some other option?

Thanks
Andrew

 

[masona]

You can but when the insulation is compressed the heat saving would be reduced. It's best to add an extra joists to allow for the thickness of your insulation. You should batten out the joists to accommodate the extra insulation thickness and should have a gap under the floorboards to prevent any condensation under the floorboards. If you don't want to add the joists thickness then you could use 4" insulation which will give you approximately 1" air flow as your ceiling joists is 5". Insulation slab are 2" thick or you could use loose-fill insulation. What I normally do if the insulation is flush to the top of the joists is to use 3"x1" batten in opposite direction then boards on top of that so it will give you a cross air-flow and no need to notch out the joists for the cable or pipe.

 

[anna preet]

Hello. ive bought loads of glass fibre insulation to top up my insulation but now found that the joists are not tall enough to fit anymore insulation in. Ive read about putting battens on top of the joists to increase the height, but i dont understand what a batten is.
Do they come in all lengths and sizes and do i just screw it ontop of the joists in the same direction?
I read in one of the posts that someone couldnt increase the height of the joists cos it would be too dangerous on the plaster and lathe beneath. How do i find out whether this is the same for my house? Do i need to just tear out my old insulation, give back the top up insulation to the shop and buy the same paper insulation that the other guy bought?

 

[masona]

Hello. ive bought loads of glass fibre insulation to top up my insulation but now found that the joists are not tall enough to fit anymore insulation in.

Doesn't matter unless you want to board the loft.

Batten is normally 2"x1" timber and it's also carpenter laungage!

 

[anna preet]

i do want to put some flooring down so i can start storing stuff up there and so i can easily paint the beams with anti rot stuff. Theres a lot of white mould appearing on most of the beams.

any help would be muchly appreciated.