New insulation over boards in loft

12 Nov 2008
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United Kingdom
I have a question about getting our loft insulation upgraded.

We currently have some old insulation between the joists (only an inch or two thick) and most of the loft has been boarded over (not insulating boards or anything special).

We don't need the storage space, so pulling up the boards and old insulation is still an option, but it is going to be a nasty job, and one that I would prefer not to do!

Can the new insulation (250mm rockwool) be laid over the boards, or should we pull them up and remove the old insulation?

Many thanks.
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No reason why it can't go over, cover the tops of the joists by crossing the insulation at right angles to them. The old insulation will still be doing it's job, dirty or not.
not as well it won't.. once all the air gaps are filled with dust there are no air pockets to trap air.. so you're relying on just the thermal resistivity of the insulating material, not the trapped air..

if you use the solid insulation boards ( kingspan or similar ) then you can board over the top of them again later if you need to for storage..
Thank you for the replies.

It seems there is no definitive answer.

The only thing I can think is that by removing it all, we can't be doing anything bad. If we leave the old insulation and boards, there maybe draughts between the insulation and boards, and that can't help. This might only be a small risk, but I don't want to do it, and then have to start all over again!

Presumably the contractors ought to let me know if there is a risk.

So I am tending towards getting the whole lot up!
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Definitive answer.

The old insulation will still be keeping some heat in, dirty or not it's still better than none. So leaving it in situ will not be worse than taking it up.

If you have no desire to use the loft space in the near future then you can go over all the existing. no point in making work for yourself.
The insulation, being soft can be laid to fill all gaps so there will be no draughts. Any gaps under the existing boards will be beneficial to trap warm air.

Only thing to bear in mind is to not stuff it into the eaves, leave a couple of inches above the insulation where it meets the rafters. This will allow air from the outside to enter the roofspace and ventilate the rafters above the insulation.
You may also need to consider your electrics, as the cables shouldn't be trapped under insulation.

Presumably where the boards are, the cables run underneath. But where there are no boards, you should try to keep the cables above the new insulation.

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