Unbraced underfloor framing.
This house collapsed after an earthquake due to unbraced underfloor framing

Are your jack studs and your wall framing braced?


Jack studs and wall framing under a floor are vulnerable to sideways motion and need bracing to prevent them from moving in an earthquake.

To check

  • Is your under-floor framing properly braced?
    Check that you have at least one of the following:
    • Your floor has a bracing sheet fixed to the inside of the frame (see the diagamxxx)
    • Your exterior cladding is a sheet material.

If your exterior cladding is a sheet material, make sure it’s in good condition and well-fixed to the framing to provide under-floor bracing.


To brace framing under a floor, either nail a bracing sheet to the inside of the frame, or replace the existing exterior cladding with a sheet cladding that also acts as a bracing sheet.

Are the timber frames that support the floor in good order?

Due to the hills around the region, many houses are built on a slope and use timber frames to support the floor.


A damaged under-floor frame has greatly reduced strength and can collapse in an earthquake.

To check

You should see piles, then a timber frame, and then your floor joists.

  • Does the timber frame for signs of damage, rot or borer infestation?

You can test the strength of the timber with a knife or screwdriver.


If the timber is soft or breaks easily under the blade, the frame must be strengthened or replaced.

If the frame has borer holes, you can treat the timber with insecticide, preferably injected into the flight holes, to stop the attack.

Always consult a professional before dismantling, repairing or replacing any part of the under-floor framing.

Are the poles supporting your house braced and in good condition?


With split-level houses or those built on sloping ground, you’ll find a large - often open - area below the floor where the house is supported by a pole structure. Damaged, or poorly designed or constructed pole structures can twist and collapse in an earthquake, causing severe damage to the house and potentially causing it to collapse.

To check

Is your pole construction braced? You should see diagonal bracing timber bolted in place between adjacent poles.

As a guide, if more than one side of the space is open, you will most likely need bracing put in place.

  • Are your poles and braces all in good condition and well connected, with no broken or split timber and no missing or corroded fasteners?
  • Is the timber in the ground also in good condition?


If you find problems, ask a building professional or engineer to inspect your house and advise you on the best bracing option for your situation.