Loft Insulation

[GlenB]

My loft floor with 8 inch joists is currently not insulated. B & Q have rolls of insulation (200 mm thick) on offer which are marked "top-up". Would these be suitable or do I need to lay a "bottom layer" first and then build it up to the corrrect depth? What is the difference between the two?

[rabbitygirl]

The main thing is to get it insulated asap Glen. You are losing a lot of heat, i.e., money without it. Insulation is heavily subsidised at the moment and never been cheaper, meaning insulating your loft can be done in double figures now instead of treble. Go 200mm initially, then top up with 100. I did a loft in 2 cross layers of 170. Aiming for around 300 is ideal as darren says.

I work in a DIY store and have watched people descend on us in the last few weeks and buy loft insulation and poly veneer for walls etc. It's a shame people wait until now before realising they need to act to keep the warm in and bills down - and it's easy and cheap to do.

[buildersmate]

300mm is now the minimum amount of fibreglass / Rockwool required to meet Building Regulations - if one was building a new house. Older houses have nothing like this amount (unless topped-up), so it shows what additional building standards have been introduced in the last 10 years to try and avoid losing heat.
The 'correct' depth is really 'as much you can afford' - bearing in mind that once it starts splilling over the tops of the joists it gets progressivly harder to handle on installation.
It's all the same stuff - top-up, bottom layer - it really doesn't matter - just pick the least cost brand for the thickness you are seeking.

[moonshadow]

You may be entitled to free loft insulation if you are on certain benefits if not then you may still be entitled to a part grant with free installation, as you have no insulation. All the info is on this web-site:- www.freeinsulation.co.uk

[GlenB]

Thank you all for your comments which are most helpful. In trying to keep my query short I missed out some detail that might have been relevant.
The loft is fully boarded on 8 inch (200mm) joists. To allow for some other work to be carried out I have removed a section of the flooring and am taking the opportunity to put in the 200mm insulation before replacing the boards and hope to complete most of the floor area section by section.
We do have insulation between the rafters already but this needs replacing as there is insufficient space behind it for air circulation so eventually there will be insulation both at the joists and rafters.
Thanks again.