Loft insulation - help!

20 Aug 2019
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United Kingdom

The house I've moved into has about 100mm loft wool inbetween joists and is boarded out above this. I'd like to improve the insulation as I believe 100mm isn't enough.

Can I lay Kingspan directly on the boards or is this a prepostorous idea? I'm totally new to this and would be grateful for some help. I would like to improve the loft insulation without wool etc if possible but not sure how to go about doing it. Thanks!
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How are you going to get it into the loft?

Wool is better suited to lofts for a number of reasons.

I have a large loft hatch with pull down ladders. I would like to still use the loft for light storage; even if it's just a small area.
Its probably going to be cheaper to lift the boards and increase the wool insulation, then add lifter joists or a system and rebourd. You do have to be mindful of the extra weight the joists will add.

or try something like this
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Leaving the boards in underneath an extra layer of insulation will increase the weight of the roof, which isn't ideal. On the other hand it also supports the Kingstown boards which is probably good.

The main things to watch out for are gaps. Any gaps will allow warm air to escape, bypassing your new expensive insulation.

Right or wrong I've got a section in the middle of the loft with 100mm in between the rafters, 100mm of kingspan above and then 3mm hardy board on top to protect the insulation. It seems to work and building control were out last week and didn't object.

Around the edges of the loft I've got standard rockwool to 300mm depth as it's not worth wasting Kingspan on areas that aren't suitable for storage.

The boards motorbike king linked to seem popular, but they use polystyrene insulation which isn't as good and I'm not sure it'd be good enough with just 100mm insulation underneath to meet regs. They also seemed very heavy to me. Far tougher than my choice but my loft is used for bulky stuff rather than heavy.
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You could do it. 100mm would be required to meet current standards.
What about " spaceblanket" I think its called fixed to the rafters.
What about " spaceblanket" I think its called fixed to the rafters.
If you mean the reflective foil, nope. Very good at reflecting radiative heat, if applied with a continuous air gap it's reasonable at reducing convective heating and, utterly pants at preventing conductive heat transfer.

Also quite tricky to walk in it without putting a foot through it.
There is a special multi layer blanket, you may walk on the joists, bit difficult on the rafters.
Can I lay Kingspan directly on the boards or is this a prepostorous idea?
yes, just lay it on the joists and board over with chipboard. I would recommend getting the stuff designed for cavity walls, it's a bit more expensive but easier to deal with. I think we got 75mm thickness at a decentish price which I think with the lath and plaster ceiling, chipboard above and 4 inch joists with wool between it was pretty much on the required u value.
Nowadays foam insulation is more expensive, so if you're not feeling flush and you have decent headroom then the loft legs and normal wool would be a better bet.

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