Loft insulation

[Robbox]

we just moved into new house and the loft has been fully boarded out by the previous owners. They've used t&g chipboard flooring and just 100mm of rockwool inbetween. Clearly 100mm is not enough. Do I have to lift all the boards lay the extra depth or could I simply lay more on top the boarding? It's a purlin roof, so there is a central section that is full height and we use for storage. If I can get away with laying more insulation on top the boards, I think I would lift the central section and fit 100mmm celotex to keep the storage area usable.
Can this work?

 

[RigidRaider]

Best to do the central area properly with Celotex and hope the boards aren't nailed down with ring shank nails - see the other post on here about creaky T&G boards.

And yes, on the unused areas I would just unroll more glass wool. You can get it cheaper if you look around and avoid the big sheds.

 

[Robbox]

Thanks for your advice. I wasn't sure that more rock wool over boards would be as effective as with no boards. The boards are all screwed down....lucky me! It's still going to be a PIA lifting the boards, messing about with loses wool and cutting Celotex to fit....

 

[alan333]

Not an answer to your question per se, but...
I got a report back telling me that by incresing my 100mm loft insulation by a further 150mm I'd save a whopping twelve quid per year (ok it might've been thirteen or something, I posted the exact figure a while ago on a similar topic). Personally I think that some insulation is much better than none, but loads more insulation is only marginally better than some.

 

[Robbox]

I guess the main point of insulation is a more even temperature as the heating cycles. In our old house, 300 years old, the heat just disappeared almost the moment the heating went off. The current home loses heat much more slowly.