Underfloorboard insulation -polystrene?

[Lusi83]

Is it safe to use polystyrene sheet insulation under a suspended wood floor?

Looking to insulated under floorboards in my living/dining room in new house ...have done so in current house and find it makes a big difference if you have laminate flooring (which I am going to have). I used netted up roll insulation attached from underside -but have large crawl space.
Problem is there is less crawl space in new house - would be really uncomfortable if not impossible so was thinking about using celotex or similar but even at seconds prices would be a hefty bill...(£300+) more than I would like to spend on this...its not that big a difference...

I have used Polystyrene sheets before -but that was behind plasterboard - it is much cheaper but I'm worried about the fire/safety aspect for under the floor ...(it will be under floorboards/fibreboard laminate insulation and laminate.) In the Wickes description they say suitable for any wall or ceiling ...no mention of floors...
B&Q sell 'Jablite floor insulation' which is thicker and more expensive but is just described as polystyrene....

 

[mointainwalker]

Polystyrene is safe under the floor. Why not use fibre-wool ? This has the same insulating properties as polystyrene, is cheaper and easier to fit between the joists although you have to tack/fix netting across the joists to retain the fibre-wool.

 

[Lusi83]

Thanks -
I thought it would be harder to tack up in the limited space (would need to be lying on my back with wool a couple of inches from face) and also it anyone needs to crawl under there in future they will be brushing against it in a reduced crawl space...
However have worked out it might actually be harder to get boards in snuggly
Still not sure what to do - thinking I might go down the fibrewool path but fixed up with polythene film ...so at least some kind of barrier from the scratchiness...did look at space blanket but that seems like an expensive option!
Alternatively it might be easier/less labour intensive to actually lift the boards and do it from above...skirtings are coming off anyway for laminate...