Loft Insulation Question

[gimchee]

Hope someone can help.

I'm going to be doing some wiring work in the loft so I thought it might be a good opportunity to sort the insulation out. Currently there is this very old and dirty looking stuff layed down loosely between the joists. Then there are wires straddling the joists with thin plyboard resting on top. On top of the ply is the modern yellow fibreglass insulation layed out in long strips about 100/150mm deep.

There's a certificate in the loft saying the work was done by a company back in 2000.

If I'm going to be lifting the boards to get to the wiring would it be an idea to clear out the old insulation, do my wiring and pack the newer insulation between the joists? Any guidance would be very welcome.

Tony

 

[masona]

Best to leave the old insulation alone and just top it up, too dusty and messy for no reason otherwise. Ideally the wiring should be on top of the insulation to reduce the heat in the cable. If you want to floor the loft, put down 3"x1" timber flat way and join the boards together on the centre of the 3"x1". This will give you a cross air-flow under the boards and protect the cable above the ceiling joists as you don't have to notch out the ceiling joists for pipe/cable.

 

[gimchee]

Thanks for that Masona.

Does fibreglass insulation lose lots of its heat saving value by packing it tightly beneath boards, rather than layed out losely in the conventional way? The company that insulated the loft really layed it on thick. In some places there are three layers (approx 12-18" thick)!

 

[masona]

I'm afraid 250mm thickness is the new building regs in the UK on new home. I've been told the extra 150mm on top of the 100mm old insulation doesn't make a great deal of difference in heat loss I've used silver foam sheet under the air-flow floorboards above the ceiling joists to help the heat loss.