Where possible, crawl right under the house, taking a large torch to examine the ground, piles, fixings, bearers and joists. If there is insufficient space to gain access, consider digging a narrow access trench between rows of piles; but if you do this, take care not to undermine the piles.

If foil insulation sheeting has been stapled under the floor, take great care. In some cases steel fixings have penetrated a subfloor cable, making the foil electrically live. Several people have died from electrocution as a result of this. Repairing or retrofitting foil insulation has been banned.

You can check for rot in timber piles or other timber with a screwdriver. Try to push it into the timber - with timber piles, do this just below the ground surface – and if the screwdriver easily enters the timber, then the timber is rotten.

Besides rot, check for:

  • high levels of ground moisture or water ponding
  • mould or fungal growth
  • pipe or cladding leaks
  • water droplets on the timber or concrete foundation walls
  • materials stored under the floor restricting air movement
  • borer attack of subfloor timbers
  • missing or corroded fixings between piles and bearers
  • lack of bracing between piles and bearers or joists
  • loose timber wedges between piles and bearers
  • piles that have been undermined by excavation
  • damaged or missing subfloor insulation.

Where there is no effective insulation, new insulation designed specifically for subfloors should be installed. Proprietary products include polystyrene friction-fitted between the joists, and segments such as polyester, glass wool or sheep’s wool that come with tabs for fixing, or are held in place by strapping. Make sure the insulation is pressed firmly against the floor so there is no air movement between insulation and floor. Exposed subfloors may require sheet material fixed under the insulation to hold it firmly in place. Repairing or retrofitting foil insulation has been banned.

The other problems on the list generally fall into one of three categories: subfloor moisture, subfloor ventilation or subfloor structure.