Yest another loft insulation question

[Broadback]

I live in a bungalow with no loft insulation at all, also there are no vents in the loft space. Placing an air brick at either end in the gables would be no problem. However being a bungalow all the cables, electric, burglar alarm et al run over or along the joists. This means, I understand that, that some insulation materials would cause a problem with the cabling, also it would be rather difficult to lay. Any ideas on what would be the best way forward please?

[Roger Mills (aka Set Square)]

As far as I know, fibreglass matting shouldn't react chemically with the plastic sheathing on the cables - but the current carrying capacity is less for a thermally insulated cable than for one in free air. It probably isn't a problem, but you need to check that the cables will still be up to the job once the insulation has been fitted.

[David Hansen]

On Thu, 16 Mar 2006 15:40:02 +0000 someone who may be Broadback wrote this:-

Is there enough slack to lay fibreglass roll insulation under the cables? If not then the cables will need to be derated appropriately and checked to see if they are still of adequate size. The lighting cables will perhaps be alright, other circuits will probably not be alright unless the rating of the protective device is reduced.

An alternative might be to use a thinner form of insulation that is just as effective. This might be thin enough to go under the cables. How deep are the rafters?