New attic insulation sitting on top of old?

v638sg7k1a92bx

I want to out a floor in my attic but wondering what to do with the insulation? There's insulation already rolled out in the attic but it sits in top of old insulation that's between the joists. Could anyone suggest what to do with this, leave as is or remove the old stuff and put the newer insulation between the joists and the put the flooring on top?

https://imgur.com/a/PAY54hA

Lumen

Leave the insulation in place and fit some loft legs or make your own to raise the floor over it.

v638sg7k1a92bx

Lumen wrote: »

Leave the insulation in place and fit some loft legs or make your own to raise the floor over it.

But you lose precious head height doing that...

looksee

You basically can't have it both ways. The main aim is keeping heat in the house, losing a bit of head room in a place used for storage is a minor consideration.

Calibos

Why does no one recommend loft roll between the joists and insulated tongue and groove fibre board attic flooring with the foam insulation glued to the back of the flooring?? 95% of the insulation efficiency gains is in the first 150mm of insulation anyway and beyond that is a case of rapidly diminishing returns from what I've heard. ie 100-150mm of loft roll between the joists depending on the depth of the joists then another 50mm of foam insulation on the back of the attic flooring boards. Why does everyone seem to chase the 300mm of insulation under stilts if need be when you are only gaining that last 5% of efficiency?? I don't understand it??

Lumen

Depends what you're using the attic for. Insulated walkboards directly on the joists between and around hatch and tanks are normal detail even in attics insulated using rolls.

You'd want to be careful with detailing if using insulated boards over joists, because if there's any gap between the underside of the boards and the loft roll, there's going to be a draught channel from the eaves which will negate the benefit of the insulated boards.

Car99

Put solid insulation kingspan or similar between the rafters then the ceiling hoist insulation wont be needed .

v638sg7k1a92bx

Car99 wrote: »

Put solid insulation kingspan or similar between the rafters then the ceiling hoist insulation wont be needed .

But then you'll just have a warm attic/storage room? Is it not better to keep the heat in the downstairs of the house?

dathi

Calibos wrote: »

. Why does everyone seem to chase the 300mm of insulation under stilts if need be when you are only gaining that last 5% of efficiency?? I don't understand it??

because 300mm of insulation is the simplest way of complying with the building regulations requirement of a u value of 0.16 w/m2k part L TGDs section 2 existing dwellings