Insulating loft on top of existing chipboard

The previous owner did a very thorough job of boarding the loft in our house. Every bit is covered, however hard it is access, each board is fairly small and has several screws in it which makes them a pain to remove as I found out when doing some rewiring.
The boards are directly on top of the ceiling joist so there is nowhere enough insulation up there, if I was to just lay an extra 200mm on top of the boards would that be OK, I thought I’d heard somewhere that it was not recommended but I don’t see why?
I’d still need some storage in the loft so I’d either raise an area or just leave that bit with no extra insulation.

I just bought 140mm kingspan from ebay, factory seconds. got 24m^2 for £170 delivered. You could easily walk on top of the stuff, just lay that down on your existing boards and tape the seams. 140mm of kingspan = 280mm of rock wool or what ever else. Search for “insulation boards seconds” on ebay or google should get a few suppliers.
I’m laying it straight on top of the joists and then laying board on top of that. (obviously got 100mm of rock wool between the joists)

Remember you’ll need to get it into the attic so depending on the size of your hole :O you might need to cut it down.

We had British gas out to look at our loft insulation. They reckoned we’d save about £12/year on our gas bills by going from the 100mm we’ve got to the 250mm (?) that’s recommended now. So not really worth doing.

We’re in a mid-terrace with an A rated boiler, so probably fairly low on use, but you might be in a similar position. Obviously, you might be doing it for ‘green’ reasons rather than for the ££ saving.

The boards are directly on top of the ceiling joist so there is nowhere enough insulation up there, if I was to just lay an extra 200mm on top of the boards would that be OK, I thought I’d heard somewhere that it was not recommended but I don’t see why?

I did this, made a big difference.

The main risk is over-insulating electrical cables as it reduces their capacity to safely carry current. I know what cables are where in my house as it was all re-wired so I can avoid/mitigate this.

The previous owner did a very thorough job of boarding the loft in our house. Every bit is covered, however hard it is access, each board is fairly small and has several screws in it which makes them a pain to remove as I found out when doing some rewiring.
The boards are directly on top of the ceiling joist so there is nowhere enough insulation up there, if I was to just lay an extra 200mm on top of the boards would that be OK, I thought I’d heard somewhere that it was not recommended but I don’t see why?

My parents had the same situation: they just laid the insulation over the top, but used the stuff that comes in foil/ plastic wrap so there was less mess. They left one area without insulation for storage, and always have the option to move the insulation bags around as needed.

All this was done a few years ago and I’m not aware of any problems.

They reckoned we’d save about £12/year on our gas bills by going from the 100mm we’ve got to the 250mm

Really, is that all?! Our ceiling joist are only 75mm though so I guess it would be more, still the payback would be over 10 years.

The main risk is over-insulating electrical cables as it reduces their capacity to safely carry current. I know what cables are where in my house as it was all re-wired so I can avoid/mitigate this.

Only ceiling lighting cables to worry about and all are LED bulbs so I don’t think it will be a problem.

Really, is that all?

Apparently so, topping up the insulation doesn’t do as much as you’d hope : http://www.energysavingtrust.org.uk/domestic/roof-and-loft

More info:
Current Insulation level / Savings/year by Increasing to 270mm / ROI based on cost of £300
None £173 2 years
12mm £111 3 years
25mm £71 4.5 years
50mm £44 7 years
75mm £29 10 years
100mm £13 23 years
150mm £7 43 years

Maybe I wont bother

The BG man told us we were better off just boarding the loft with t&g board to minimise drafts. He said he’d done the same in his loft.

I put a couple of 100mm kingspan boards across the rafters in ours. In doing so I discovered that it had previously been topped up with another layer of rockwool already but then squashed down by overboarding, so pulling the top-up stuff out meant I got a load more rockwool to use on other bits of the loft. Win… 🙂