Subfloor – deterioration of the underside of particleboard flooring

Cause

The particleboard is too close to the ground 

Repair

  • providing greater subfloor clearance through repiling is the best long-term solution, although this may be expensive or impractical. Aim for at least 300 mm space below bearers, or 450 mm minimum (to allow crawl space) or ideally 550 mm for particleboard flooring

  • where achieving the required clearance from ground to flooring is not feasible, consider excavating narrow trenches between the rows of piles to increase ground clearance and airflow, taking care not to undermine piles 

  • lay 0.25 mm thick polythene sheet to cover the ground under the house. Ensure that the ground is shaped so no water accumulates on the polythene. Sheets should be lapped a minimum 75 mm (preferably taped) and tightly butted to foundation walls/piles. Weigh down sheets with bricks or concrete to avoid them being displaced by air movement.

  • ensure that the floor dries out completely. Check the extent of damage to the particleboard – part of the flooring may require replacement.

Cause

The subfloor space is very damp 

Repair

  • identify any leak in a pipe or appliance and make a permanent repair. (Work on waste pipes must by law be carried out by a licensed or certifying plumber)

  • if rainwater gets under the house, divert surface water away from the house by lowering the ground levels around the building and sloping the ground away from the house

  • improve airflow under the house:

    • clear away obstructions such as planting or soil build-up at vents around the house perimeter

    • clear away items stored under the house blocking airflow

    • provide not less than 3500 mm² of clear open subfloor venting (grilles or gaps between baseboards) for every 1 m² of floor area

    • spread vents evenly around building perimeter for cross-ventilation

  • where necessary, create new ventilation:

    • replace/refix baseboards to allow space for air movement

    • install new ventilation grilles in sheet cladding/bracing 

  • cut additional ventilation openings in concrete or concrete masonry foundation walls and installing surface-mounted proprietary grilles. Take care that openings are not formed in the top course of the blockwork and that reinforcing is not cut 

  • lay 0.25 mm thick polythene sheet to cover the ground under the house. Ensure that the ground is shaped so no water accumulates on the polythene. Sheets should be lapped a minimum 75 mm (preferably taped) and tightly butted to foundation walls/piles. Weigh down sheets with bricks or concrete to avoid them being displaced by air movement.

  • ensure that the floor dries out completely. Check the extent of damage to the particleboard – part of the flooring may require replacement.

Cause

There is a water leak from within the house

Repair

  • identify the source and location of the leak. Make a permanent repair, or call a licensed or certifying plumber to make permanent repair. Work on waste pipes must by law be carried out by a licensed or certifying plumber.

  • establish whether the leak is likely to be a one-off problem or stems from old deteriorated pipework or a design or materials fault that may recur. If the latter, discuss potential long-term solutions with a licensed or certifying plumber or NZIBS building surveyor

  • if the leak comes from a fixture or appliance that is very old and a permanent repair is difficult, consider replacing the fixture/appliance

  • ensure that the floor dries out completely. Check the extent of damage to the particleboard – part of the flooring may require replacement.

Cause

There is a leak through wall cladding leak if the cladding is damaged  

Repair

  • first locate the leak in the wall cladding and make a permanent repair. If you cannot locate the leak or you find significant rot in the wall framing, consult a registered building surveyor

  • ensure that the floor dries out completely. Check the extent of damage to the particleboard – part of the flooring may require replacement.