Earthquake Retrofitting: What Actually Helps an Older House

Many New Zealand homes were built before today's bracing and connection rules existed, so when people talk about "earthquake-proofing" an older house, the honest answer is that you can't make it earthquake-proof - but you can make real, measurable improvements. Research from the Natural Hazards Commission (NHC, formerly EQC) and BRANZ points to a handful of upgrades that consistently reduce damage and risk. Here's what the evidence actually supports.

Start under the floor: foundations and bracing

Older piled foundations are consistently the weakest link in timber houses, particularly pre-1940s homes that rely on ordinary piles or soil friction rather than proper bracing. BRANZ research on sloping sites found that many of these subfloors lack a solid connection between the timber frame and the piles at all.

Practical fixes that have been tested and shown to work include:

• Fixing bearer-to-pile and bearer-to-joist connections where they're missing, using wire, bolts or brackets
• Replacing rotted or deteriorating piles
• Adding diagonal bracing between piles, especially where the subfloor clearance is more than 600mm
• Casting infill concrete walls between existing piles on sloping sites - BRANZ testing found this very effective at stabilising isolated pile foundations
• Nailing plywood bracing to jack stud walls, with galvanised brackets at stud-to-plate joints

Because the strength of old bracing walls is often unknown, BRANZ has also developed tested bracing ratings for older systems, which gives an engineer a real number to work with instead of a guess.

Chimneys: the highest-risk item above the roofline

Unreinforced brick or concrete chimneys, common on pre-1970s homes, are one of the most dangerous features in an earthquake because the section above the roofline can fail and fall. The options, in order of how much they help: remove an unused chimney to floor level (most effective), replace the hazardous upper section of a working chimney with a lighter metal flue, or - as a lower-cost option - add bracing in the roof space between ceiling joists, which helps protect occupants from falling debris but won't stop the exterior collapsing.

Quick wins worth doing regardless

Not every improvement needs a builder. NHC's QuakeSafeYourHome guidance highlights several low-cost items that genuinely reduce damage and injury risk:

• Hot water cylinders: strap them to the wall framing - two straps for cylinders under 200 litres, three or more for larger ones
• Header tanks: block and tiedown strap them to the roof framing, or remove if unused
• Tall, heavy furniture: screw to wall studs with angle brackets
• Gas bottles: secure on a level pad and chain to the house
• Solid fuel burners: check restraints against the manufacturer's instructions - poor installation can also affect insurance cover

If you're already renovating, it's the cheapest time to do this

Trade guidance consistently makes one point: bundling seismic upgrades into renovation or repair work already underway is far more cost-effective than doing it as a standalone job. If wall linings are coming off anyway, that's the moment to upgrade bracing - brittle lath-and-plaster linings can be replaced with modern plasterboard bracing, and older timber bracing can be assessed and counted toward the building's overall rating.

When to bring in a professional

Some of this is genuinely DIY. The rest needs a licensed building practitioner or a structural engineer, particularly:

• Chimney removal or replacement
• Assessing and strengthening pre-1950s masonry or pre-1930s lath-and-plaster walls
• Foundation bracing decisions, especially where the perimeter foundation isn't continuous or subfloor clearance exceeds 600mm
• Retaining wall assessment where there's cracking, bowing or drainage issues

If you're planning a renovation on an older home, or just want to know what a retrofit would realistically cost and achieve, get in touch with Fil Engineers - we can tell you which upgrades will make the real difference on your specific house.

Sources

• Natural Hazards Commission - QuakeSafeYourHome guide (2025)
• Wellington City Council - Earthquake resilience checklist
• BRANZ - Retrofitting timber house foundations on sloping sites
• PlaceMakers Under Construction - Always look for quake improvements
• Natural Hazards Commission - The adequacy of existing house foundations to resist earthquakes

This article is general information only and isn't a substitute for site-specific structural engineering advice. Every house and site is different - talk to a professional before carrying out any structural work.