Loft insulation - replace existing or overlay ?

[mikeyw]

Guys,

I was lucky enough to snap up 18 rolls of 170mm insulation for £18 in the Npower promotion. Tomorrow I have unfortuneately the task of laying it all

My loft presently has insulation between the joists so I was simply planning on laying this new stuff over the top of existing probably giving around 300mm in total.

Is this the best approach or should I simply just replace what's there with the new ? - this will be a ballache having to cut the correct width so rather avoid unless absolutely vital.

Also I've heard you should try and avoid laying over electrical cables on joists - how is this possible if the cable is attached to the joists ?

Is there such a thing as too much insulation ie 300mm ?

 

[Chukka63]

just lay the new insulation on top at 90% to the existing BUT make sure you dont block up the air gaps or you will get condensation problems

 

[mikeyw]

Thanks - what's the best tool for cutting the stuff up in the loft ?

 

[PrenticeBoyofDerry]

You should avoid completely surrounding the cables with thermal, insulation as the heat from the cable can not be dissipated and it will reduce the current capacity that the cable can safely carry, it could quite easily half it.
If your overlaying on to the cable, make sure that the cable is not surrounded.

The cutting tool depends what type of insulation you are using, but a jack saw is usually quite good.

 

[foxhole]

Good old kitchen bread knife, serated edge.

 

[Chukka63]

bare hands

 

[PrenticeBoyofDerry]

bare hands

Teeth