Insulating / boarding loft --- best compromise?

[mike]

I'd like to partly board the loft for storage but also beef up the insulation.

Currently there's fibreglass between the 2"x3" joists - so < 75mm insulation.

The celings below are 1930's lath-and-plaster meaning the effective depth between joists is probably reduced to 60-65mm, and I don't want to do anything to jeopardize them because I think it's only the vinyl wallpaper the previous owner installed that's holding them together.

I don't want to spend a fortune and end up waiting decades for pack back, and I don't want to start a major engineering project either.

Current plan is to board over the central area and lay either 170mm or

2x100mm at right angles to the joists over the unboarded area.

I've thought about putting Celotex/Kingspan under the boarding but I'm not sure the extra cost is justified.

I realise insulation/storage/cost will always be a compromise but does the above seem like a reasonable plan?

And do the lighting cables have to be extended to be above the fibreglass to supply a modern low-energy CFL?

Thanks for any advice.

[Phil L]

If your ceiling joists are 80 year old 3X2's, i wouldn't risk putting anything up there

[NT]

sounds ok. You can also put some insulation atop your boarding, and jsut peel it back where boxes are placed.

In practice they never are. If theyre resting on the plaster that can conduct enough heat away. Its when theyre surrounded on all sides that things can get hot.

Loads of old lofts are on 1.5-2 x 3-4. As long as the spam isnt excessive, and it normally isnt, they can be loaded up fairly heavily. Such joists bend long before they fail.

NT

[John Rumm]

Depends on how much you want boarded. You could have 10 sq m of 50mm PIR foam for under £50 - combined with the existing 70mm of wool, that would give you the equivalent of say 170 - 200 mm of fibreglass.

Not usually - they are sufficiently overrated for a 6A MCB anyway.

[mike]

Thanks for the replies.

Is it acceptable to put Celotex across joists, board over the top and screw through?

[John Rumm]

Yup.

[mike]

Thanks!