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loft insulation guidance please

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markppearson:
For your trusses, I used polythene sheeting to keep any chance moisture penetration out, then used foil backed 12.5mm gyproc (foil facing roof tiles) and taped it up and then painted over it.

For the flooring, the full thickness is a legal requirement except on new builds where possible.  25mm, boards would be best to give you stability and strength. If you want to compensate for the loss of insulation, then you could again use 12.5mm gyproc under the boards. These will also provide you with a bit of sound deadening if you are planning to use it a 'room'.

carbore:
I recently had a lot of work done on my house and would say the following.

Insulation is the most cost effective (fastest retun on investment) way to save money/be green. Forget about ground source heating/solar etc unless you can wait 7-10 years. Good insulation is has a very quick payback, so what im saying is its worth investing in as much as you can afford (and then some).

Secondly, id never take any risks re fire safety as mentioned.

There are often grants for lof insultaition, but they come with strings attached, it may be worth looking around as much as possible to see if you can get some money towards it, but unfortunatley its usally schemes where people fit it for you, as opposed to DIY.

Thirdly, remember that Energey efficiency is part of the HIP (Home Inspection Pack) so again its worth doing properly to make your house better on this scale.

Im sure you only want to do this once, so take all advice going before proceeding.

Also re products, we used various including a silver blacket type thing that went in the studwork. better than traditional fibregalss wool.

winchman:
I was going to buy pannels of polystyrene loft insulation that was half the thickness of wood so air can still get between the felt and polystyrene and put hard board up to hold the poly in place. Mum was talking to a friend the other day who said I should use thin boards that are covered in silver foil each side and lay them 90 degrees to the trusses. Which way is best?

Stop now!!
If you insulate the loft floor and the bit under the felt you may get condensation under the felt.
I know I have done this but only got a small bit done before we found the problem.
I will post more detail later when I have more time

T30CDB:
Not wanting to throw a spanner in the works but firstly what size are your ceiling joists ( the emphasise is on the word ceiling not floor joists ) as older houses only had sufficient sized timbers to carry the weight of the ceiling not a floor. If you wish to add extra insulation in between the ceiling joists and then board it i would recommend enhancing the existing ceiling joists with another timber of equal thickness to provide extra strength and ensure that it gets as close as you can to the external wall plate as possible and fixed to the jack rafter as well as finishing on top of any structural walls. so if you only have 3 inch x 2 inch or 75mm x 50mm timbers these will definitely need doubling up. Don't nail your boards down as any electrician in the future that needs to get them up will curse you for ever and a day.

muddyjames:
I have a mid 90's built house. I did think about the weight but there used to be a water tank but that was removed when the combi boiler got installed. also my house isnt very big either so the stud work in my 2 walls up stairs are about a 1.3 of thr way in from each end of the house giving some support to the ceiling joists. I know they arent supposed too but not a huge amount of weight has been added with the removal of the water tank.

So if I dont insuklate the rafter space then, can I just board it over with hard board to keep drafts out and to act a bit like insulation but not? I only want to board out the top half of the trusses.

cheers

james

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