Questions about improving the insulation in my loft

[Rob Horton]

My loft has a minimal amount of insulation that was probably put in about 20 years ago. The house was built in 1984 and the loft is pitched, unheated and ventilated.

Not sure of the correct terminology, but I refer to joists as the horizontal wooden beams in the loft that the ceiling is fixed to and what you actually walk around on. Rafters are the sloping wooden beams that the sarking and tiles are fixed to.

(1) I want to add more insulation. Current regulations say 270 mm for glass wool, 250 mm for rock wool, or 220 mm for cellulose. Are there any other rollable insulation systems that have a higher level of insulation thus needing less height?

(2) If I need to add height to my joists, (it's a small house and need to use the loft for storage) can I lay wood strips (of the same dimensions as the existing joists) on top of the the existing joists? How do you fix them in place, glue and the occasional nail or screw?

(3) I have electrical cables in the roof, although these are for ordinary electrical lighting. Is it OK to have these covered by the insulation? The cables are already covered with insulation by the previous insulator/owner.

(4) Although it is an unheated and ventilated loft, will I get any benefit from adding insulation between the rafters? I want to use some thing that is enclosed in an aluminized bag so that it will (hopefully) reflect some heat away during the summer.

Thanks.

[Stuart Noble]

Not rollable. Celotex between the joists would be the alternative, but more work, and a lot more money.

Rockwool slabs between rafters works well if you use the loft enough to make it worthwhile. Nobody seems to have much faith in the aluminium/bubblewrap sandwich stuff you see in the sheds

[David Hansen]

On Thu, 15 Mar 2007 10:36:04 +0000 someone who may be Rob Horton wrote this:-

You can do. A better strategy is to top up the existing level to the top of the joists and then lay rolls of insulation material at ninety degrees to the joists around the edge of the loft, leaving a central core that does not have this extra insulation or adding boards above just the central core if this does get extra insulation.

Lightweight items can be stored on top of the insulation and heavier items stored in the central core.

Remember not to insulate under water tanks.

Probably. Make sure there are only lighting cables though as the cables of other circuits don't have as much capacity in reserve.

[John Rumm]

Yup, that would be my understanding also.

Not that I am aware of. You would normally need to go to the rigid foam board systems like celotex etc to get more insulation in less space.

If you don't need to store stuff in the space, then insulation just laid counter to the exiting (i.e. across the joists rather than between) will actually work better. No need for extra joist depth.

If you do want to floor it, then you can extend the joist height (screws would be my favoured fixing since there is less chance of damaging a ceiling with hammering). Alternatively you can use a roll insulation between the joists, and a foam board over them, with the floor directly fixed through it. If you only do a section like this is is not as expensive, and it is quite easy to do.

FFFFFFFFFFFFFFFFFFFFFF insulation? The cables are already covered with insulation by the

Lighting cables usually have sufficient spare capacity that the derrating effect of the insulation is not a problem (assuming your lighting circuits are protected with a 5/6A Fuse/MCB). Take care that other circuit cables are not buried though.

Depends on whether you want have a "warm loft" - it may make for more stable environmental conditions for things stored up there.