SR72 An investigation of 62 coastal subfloors for fastener corrosion (2007)

A total of 61 houses were inspected for corrosion of their subfloor fasteners on William Street, Petone and The Parade, Paekakariki. These streets were chosen for their established housing and proximity to the sea.

From the houses on William Street, which runs perpendicular to the coast, it was concluded that, although sea salt undoubtedly contributed towards fastener corrosion, no correlation was evident between the exact distance from the sea and the extent of corrosion.

By analysing case histories where fasteners had either performed unusually well or unusually badly (from the houses on both William Street and The Parade, which runs parallel to the coast), useful insights were gained that provide information as to what measures are necessary to ensure that structural fasteners have a useful life of 50 years as required by the New Zealand Building Code.

Excluding sea salt from the subfloor is very important in coastal locations but not at the expense of all ventilation, as dampness will accentuate salt corrosion problems, as well as causing other dampness problems in the house. For houses on very dry ground well above the water table, ventilation is less important.