Loft boarding

9 Dec 2009
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United Kingdom
I'm going to reinsulate my roof space during the current project to board the loft out for light storage.

I know that the recommended depth of the final insulation is 270mm with two layers of insulation laid both ways, but with my strengthened floor joists (new 3x2s on top of existing 3x2 joists, hung at each end from 6x2 purlins) the depth is going to be 150mm, ie 75mm (3") x 2 and then with the loft boards on top.

What sort of insulation do I put down? Just top layer, just bottom layer, two layers on top of each other under the boards, what thickness etc?

What should I be doing for a boarded scenario?
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are you extra joists going across the old timbers at right angles, or on top of them, or what?
Pass :LOL: smoking :LOL:

Only joking mate, this is when I did mine and I just rammed to spaces between the joists with insulation.

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are you extra joists going across the old timbers at right angles, or on top of them, or what?

On top of them, along their length, not at right angles, and then hung from the floor purlins at each end from joist hangers and tied together in the middle both sides with 4-hole long thin repair plates.
then you will have to put the initial insulation between the timbers, as thick as you can get without squashing it down. If there is any suggestion of condensation, leave an air gap under the boards. It may be an advantage to use Space Blanket or similar, which has the plastic wrapper, to prevent any moisture passing through the lowest quilt.

Over the top of the timbers, you can choose any one of:


-extra layer of quilt, laid at right-angles to the timbers to prevent gaps

-extra timbers at right-angles to the existing, with another layer of quilt between them and floorboarding screwed to these cross-battens

-a layer of rigid plastic foam insulating board, with the flooring on top
So when you say "floorboarding" is one of the options over the base layer, are you saying that the boarding itself affords a level of insulation.

Having seen all the answers, my inclination is to put a 100mm base layer between the floor joists, which with two 3x2s on top of each other = 150mm joist depth and 100mm insulation depth leaves 50mm air gap under the boards. Would all that be acceptable?

I truly don't fancy having to put yet another layer of joists at right angles with more insul between them, from both the cost and time point of view.

As this is a light storage project, ie not requiring planning/building regs, I intend to take progress photographs to show anyone who enquires about the loft project when I come to sell.
Simon if you look at my post on R values which is about four down from this it can be done easier with vermiculite granuals if you fancy them .

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