Here are some options for floor construction from CAT's eco-building experts:
Either: a suspended, well-insulated timber floor of homegrown soft or hardwood joists and floorboards. Good draught-proofing of the floor and ventilation of the underspace are vital. The underfloor space sealed with a recycled polythene membrane and covered in local granular fill or recycled aggregate.
Or: a solid limecrete floor using recycled aggregate, laid on insulation. Lime can be used to stabilise earth or hemp as a floor base and finish, but should not be covered with an impermeable material (such as linoleum). A damp-proof membrane of polythene or bitumen.
These are in preference to concrete (joists and slab, with plastic foam insulation) or chipboard (above concrete slab, etc).
First preference for homegrown soft or hardwood tongue-and-groove timber floorboards on homegrown softwood joists with timber lath & lime plaster or plasterboard underlining. Second preference for a similar method but with plywood board or OSB (oriented strand board) floor.
These preferred to a concrete beam and block floor or chipboard.
Timber flooring is sustainable as long as new trees are planted to replace those that are used. The best guide at present is the FSC certification mark, which shows that the wood has been sustainably harvested. Most flooring is of hardwood (from deciduous trees), but some 'softwood' (from evergreens) can be more durable than some hardwood, so could be suitable for flooring.
Another sustainable option is reclaimed timber flooring, which could come from old schools, chapels, etc. You could look for local suppliers of salvaged/reclaimed materials, or use websites such as www.salvo.co.uk or www.communitywoodrecycling.org.uk
Using timber in your house could even help fight climate change! In their natural cycle trees absorb carbon dioxide during their lifetime and this is released as the wood rots away (or is burnt). By using wood in buildings we are locking up this carbon and preventing it from re-entering the atmosphere.
This information about existing floors may also be useful:
Older homes may have solid floors (stone, tiles, etc) laid directly onto soil or cinders that depend for insulation and dryness on the earth underneath them being kept dry. To work, the ground level outside needs to be lower, with good drainage around the house. These floors can fail when an impermable finish (e.g. linoleum or plastic) is added, trapping moisture underneath and negating the insulation value of the soil. Suspended ground floors may have had joists built into the external walls, causing the ends to rot if the walls became damp. An unventilated underspace could also lead to damp damaging the joists.
More recent homes are likely to have a solid concrete slab, laid on a DPC of polythene and hardcore fill, with insulation from a 'floating' floor of polystyrene with chipboard flooring or a sand/cement screed. Suspended floors of either timber joists on steel hangers with insulation suspended between and chipboard or timber floorboards, or of concrete joists & blocks.