Loft Insulation

[Broadie451]

Hi There I would like to renew my existing loft insulation. At the moment we have a granular type insulaton which was ok but we've since had an extension to the house and I would like to renew the old stuff. The problem is the joists in the original part of the house are only 75mm (3") deep. I would also like to lay loft type floor boards over these 3" joists to keep the loft clean and make getting the Christmas decorations as easy as possible (I'm getting too old to keep on with my Indiana Jones impressions as I try and cross the loft to the decorations)
Would a solid foil backed insulation board such as kingspan be a better solution instead of using a fibreglass type blanket.

[mrknowall]

This doesn't answer you question but might help with the costs

You may well be eligible for a grant of 30% - 70% for your home insulation - whatever your income - and for a 100% grant if you are on certain benefits or tax credits.

[heathfield]

Hmm. It sounds like your joists are merely ceiling joists, only there to support the ceiling. At just 75mm, they don't sound like they're sturdy enough to take a floor.

Maybe Buildersmate could confirm this?

[Broadie451]

Heathfield I think you spot on with your answer about the thickness of my joists. I'm not after converting my loft into a living space but I would like to be able to move around up there when I need to, ie to retrive the usual junk.
Having already put a size 9 through a ceiling, I thought this would be the ideal opportunity to board the loft out and prevent any further need to install another velux in a completely random place.
Or do you think the joists would be under sized?

[buildersmate]

You'd be OK to put chipboard floorboards down, but don't go overloading what you put up there - its very tempting to do so.
Kingspan / Cellutex is a far better insualtor than fibreglass - about 2x better, so 70mm thick slabs put in the joists would be equivalent to 140mm of fibreglass. Its more than twice as expensive (for the same thickness), but given you have a fixed depth, that's your best solution. Both products are better than vermiculite - can't remember by what factor.
As to whether you can get a grant, check with LA. I suspect you can't as there's some insulation already up there - unless you clear it all out first?

[Broadie451]

Thanks for the advice, Buildersmate and also Heathfield. You are bang on with the vermiculite, I've mentioned it a couple of times in the past to other people, and they just looked at me with a blank expression. I'm glad to find out its not a good insulator cause I wasn't sure if this was the right direction to going in, when I started shovelling the vermiculite into bin bags. I'll start looking for some 70mm kingspan type insulation on some of the online auction websites. Would you go for the treated or untreated chipboard flooring. Once again thanks for the advice.

[rabbitygirl]

During some previous renovations we used Kingspan to insulate a single skin wall during conversion of an attached outhouse to habitable room. I had seen a material akin to bubble wrap but foiled on both sides claiming to be equivalent of 2" insulation. So I used this as well!. The local build inspector had not seen this before (?!) and I cut him a sample to take away. Confident we have left new owners with additional 2" insulation. Convinced its a great product, reasonably priced, found in Wickes and Screwfix etc and SOoo easy to use - just cut to size with scissors. Kingspan however, great product, but cutting it is messy hard work. Will use my new find in loft of bungalow we move into shortly and top up with a quality thick fibreglass (or similar).

[buildersmate]

The product you refer is a multifoil product that is very thin but is claimed to have amazing properties. It got a Building Regs approval for a time but the Phenolic boys (Kingsapn etc.) kicked up a fuss about it. It may have been withdrawn now because it doesn't work if it gets squeezed.