Bracing resilience check

Prototype: illustrative figures

Building codes are designed to save lives.
What would it take to save your home too?

Choose a different path
Site subsoil class

Defaults to site class C.

Enter the total earthquake and wind bracing units your NZS 3604:2011 calculation gives for each direction, summed across the whole house. For the purposes of this page, code minimum is taken as the larger of the wind and earthquake demands you enter below.

Along

Across

The black bar is the baseline target, which considers the latest seismic hazard information released since NZS 3604 was published (see technical basis section for more information). In cases where the latest information suggests a higher level of hazard than accounted for in NZS 3604, the black bar is increased accordingly. In other cases, the NZS 3604 earthquake requirements remain sufficient to account for the latest hazard information, and so the black bar is set off the earthquake bracing unit figure set by the user. The green portion on top indicates the extra bracing that BRANZ SR337 recommends adding to work towards a low damage outcome, rather than only meeting the life-safety minimum targeted by NZS 3604.

Along

Please enter all bracing unit figures above to see this plot.

Across

Please enter all bracing unit figures above to see this plot.

Indicative resilience multiplier

There are two percentages below for each direction of the home, both shown relative to your NZS 3604 governing demand (100% = code minimum). The first shows how much higher that demand becomes once scaled for the latest seismic hazard modelling. The second takes that further, adding the SR337 margin, to show what multiple might be required to achieve a low damage outcome.

Along

Please enter all bracing unit figures above.

Across

Please enter all bracing unit figures above.

Want the technical basis?

The extra bracing shown here draws on two separate sources: BRANZ Study Report SR337 (2015), which found that NZS 3604 homes may need around 50% more seismic bracing to limit damage in a design-level earthquake rather than only meet the life-safety standard, and the 2022 National Seismic Hazard Model, which has since raised our understanding of earthquake hazard across much of New Zealand (as documented in TS 1170.5:2025).

Worked example: Wellington, site class C

  1. NZS 3604:2011 groups every site into one of four earthquake zones, based on the NZS 1170.5 Z factor at that site: zone 1 is based on a Z factor of 0.2, zone 2 on a Z factor of 0.3, zone 3 on a Z factor of 0.46, and zone 4 on a Z factor of 0.6. These are combined with site subsoil class categories to give the following table of demand values - the background of these can be found in the BRANZ Basis of NZS 3604 document:
    Soil classEQ zone
    1 (Z = 0.2)2 (Z = 0.3)3 (Z = 0.46)
    A & B — Rock0.120.20.24
    C — Shallow0.160.240.28
    D & E — Deep to very soft0.20.320.4
  2. Wellington’s real Z factor is 0.40, which falls in zone 3, so its NZS 3604 earthquake bracing demand is calculated at the zone’s Z = 0.46 ceiling, not its actual Z = 0.40. For the purposes of the comparison with TS 1170.5:2025, the actual Z factor is used (Z = 0.40 in this case) in order to make use of any excess already allowed for in the NZS 3604 approach.
  3. For this example, say that zone-3 earthquake bracing demand comes out to 2,400 BU (whole house, along direction) - an illustrative figure for this walkthrough. Say in this example, wind demand doesn’t exceed this, so 2,400 BU is also the code minimum bracing for that direction of the building (earthquake governs).
  4. Calculating the TS 1170.5:2025 demand at Wellington’s real Z = 0.40, site class C, and the relevant other assumptions consistent with the basis of NZS 3604, results in a demand value of 0.37. Comparing this to 0.28 from the table above gives a raw hazard shift of ×1.32 (132%).
  5. Baseline target: 2,400 × 1.32 = 3,168 BU. Against the 2,400 BU code minimum, that’s 132% of code minimum - what this site needs to keep pace with the latest seismic hazard modelling alone, before SR337.
  6. Apply the SR337 low-damage margin: ×1.5.
  7. Low damage target: 3,168 × 1.5 = 4,752 BU. Against the same 2,400 BU code minimum, that’s 198% of code minimum, meaning this site would need about 1.98 times as much bracing as a code-minimum design to work towards a low damage outcome.

Both percentages are floored at 100% of code minimum: if the hazard shift or low damage figures work out lower than what NZS 3604 already requires, the tool shows 100% rather than a number below it, since that’s the current legal minimum regardless of what the hazard model or SR337 suggest.

Reduce the demand instead

Adding bracing capacity is not the only option.

FrontFoot® takes the other pathway: it reduces the level of shaking that reaches your home's structure in the first place, rather than adding capacity to resist it.

Learn about FrontFoot

How does your town or city stack up against others?

Here is a selection of towns and cities across New Zealand, and their relative seismic risk for a NZS 3604 structure - largest first. Dark blue is NZS 3604’s own demand for that town’s earthquake zone; mid blue, where present, is how much higher the latest hazard modelling (TS 1170.5:2025) pushes that for this specific town; light blue is the added SR337 margin on top, considering what might be required to reach a low damage outcome rather than just the life-safety minimum. Figures are unitless - useful only for comparing towns relative to each other, not as bracing units.

Site subsoil class

Defaults to site class C.

Hover over any bar to see which town or city it is

CartertonMastertonFeatherstonGreytownUpper HuttLower HuttWellingtonPoriruaPahiatuaDannevirkeParaparaumuWaikanaeLevinOtakiWaipukurauAshhurstWaipawaPalmerston NorthBlenheimFoxtonHavelock NorthKaikouraCliveGisborneHastingsRenwickFeildingGreymouthHokitikaLake HayesNapierPictonQueenstownTe AnauWairoaMartonAlexandraArrowtownBrightwaterChristchurchCromwellDarfieldKaiapoiKawerauLeestonLincolnLytteltonMotuekaNelsonNgongotahaOhopeOpotikiOxfordPegasusPrebbletonPutaruruRangioraRichmondRollestonRotoruaTaumarunuiTaupoTe PukeTokoroaTurangiWakefieldWanakaWest MeltonWestportWhakataneWhanganuiWoodendAshburtonAucklandBalcluthaBeachlandsCambridgeDargavilleDunedinGeraldineGoreHamiltonHaweraHelensvilleHibiscus CoastHuntlyInglewoodInvercargillKaikoheKaitaiaKatikatiKerikeriKihikihiKumeu-HuapaiMaraetaiMatamataMiltonMorrinsvilleMosgielNew PlymouthNgaruawahiaOamaruOmokoroaOne Tree PointOtorohangaPaeroaPokenoPukekoheRaglanRiverheadRuakakaSnells BeachStratfordTaurangaTe ArohaTe AwamutuTe KuitiTemukaThamesTimaruTuakauWaiheke WestWaihiWaihi BeachWaimateWaitaraWaiukuWarkworthWellsfordWhangamataWhangareiWhitiangaWintonChristchurch
NZS 3604 demandTS 1170.5:2025 excessSR337 low damage marginChristchurch (selected above)

Town / city

Disclaimer

This tool indicates relative demand, not a design specification. Any build requires specific engineering consideration. Preliminary information only, not professional engineering, legal, or insurance advice. Figures shown throughout this page are illustrative placeholders, not final figures. The moderate, high and extreme shift bands are illustrative cutoffs, not final thresholds. Worked-example bracing units for the curated locations, and baseline estimates for every other location, are placeholders too, not location-specific NZS 3604 calculations. The SR337 uplift factor is set from the recommendations in BRANZ SR337 for what it might take to achieve a low damage outcome.