You can buy a house that appears perfectly sound and inherit a problem you never considered.
Following the 2016 Kaikoura Earthquake, I had a number of inspections to check the state of the subfloor framing.
So what is the general state of piled houses in Nelson?
Older houses, from before the modern Building Code was introduced in 1992, often do not meet current building structural standards.
Some inspections show that pre-1920s houses can be held in place by gravity, with little fixing or bracing, or they may be supported on old tōtara stumps or brick piers, but tōtara piles can look like a tree trunk and be almost completely rotted out immediately under the ground. That will prove inadequate if Nelson is subject to a strong earthquake. That should probably read when.
Houses with substandard subfloor framing may be shaken from their piles. On a sloping site this may endanger lives.
Houses built up until 1992 may have met the standards of their time, and are not actually required to be upgraded to meet current, more stringent, requirements.
These days there are considerable construction requirements to secure a new or re-piled house to the ground. The depth of the piles, the fixing details of piles to bearers, and general sub-floor bracing. Houses built to the current Building Code are much less likely to fall off their foundations in the most severe earthquake.
When repiling, you generally need to raise the house evenly, or the plasterboard can crack and windows and doors won’t open or close.
If a house is low to the ground, access may only be through the floor, which means the carpet has to be lifted, holes cut in the floor, dirt removed, concrete poured, and the floor and covering subsequently reinstated, etc. It’s a messy operation.
So, it’s best to have an experienced repiler for this dangerous work in confined spaces. Unsurprisingly, this is expensive, and costs can be $25k to $45k for an average Stoke weatherboard house where access is good, but may be more than $80k for more difficult or larger houses where access is through the floor, and reinstatement is expensive.
Okay, that big earthquake may not happen in Nelson/Tasman in our lifetime.
Then again, if it does, yeah, it’s a significant issue.