Precast concrete piles were available in the 1930s. Original concrete piles may still be in good condition (Figure 1).
If recent repiling work has been carried out, the replacement piles are likely to be H5-treated pinus radiata, square piles. These should be braced to meet the requirements of NZS 3604.
Wire ties connecting piles to bearers should be checked for corrosion and and where there is evidence of corrosion, the ties must be replaced. Where there are no connections between piles and bearers, ties must be installed.
If new work is to be carried out, particularly if an additional floor is to be added, the foundations must be checked to ensure they are adequate for the new loadings and that there is sufficient lateral bracing in the piles (see Inadequate foundation bracing).
If piles must be replaced, they can be installed:
- from underneath the floor if there is sufficient working space (minimum 450 mm clear)
- from above the floor by cutting holes through the floor (approximately 450 mm square) or removing floorboards.
When repiling into soft ground, it may be necessary to install deeper piles in order to reach solid bearing ground. This can be done with small diameter steel pipe piles that are coated to resist corrosion. They are driven or augured down to the required level and then a concrete pile is cast around the top.
In extreme cases where the house is built on deep unsuitable ground, it may be necessary to remove the roof so that long piles (such as railway iron) can be driven down to firmer ground.
If the floor is out of level, employ a firm experienced in repiling and levelling work to jack the settled parts of the building back to as near level as possible. Piles and/or damaged subfloor framing must also be replaced to maintain the building in the level position.
This process may result in damage to external and internal wall linings and doors and windows, in which case remedial work may be required after levelling.
If additions or alterations were made to the building after the floor settled, an assessment should be made of the effect of levelling the building on the additions and alterations including fittings and services that were added after the floor settled. If levelling is not practical, or will cause too much damage to existing finishes, the floor may be:
- left as it is, if acceptable to the owner
- overlaid by a new timber, plywood or particleboard floor, packed to make it level
- where there is a ‘hump’ in part of the room due to settlement around, for example, a fireplace, it may be able to be levelled by reducing the height of some of the piles and allowing the floor in that area to settle – sometimes weighting is necessary to force the floor down.