1. What changed
An amendment to the Building Standards Act, effective 1 April 2025, narrows the "4-go exemption" and abolishes the "4-go building" classification altogether. Where wooden two-story houses used to skip structural review at building confirmation, the structural documents must now be submitted and reviewed.
2. What the old "4-go exemption" was
The 4-go exemption allowed small wooden houses (up to two stories, up to 500 m² floor area) designed by a licensed architect to skip structural review at confirmation. It accelerated permitting and reduced paperwork — but the seismic basis was not directly visible to owners or the authority.
3. The new classification: new 2-go and new 3-go
| Class | Scope | Structural review at confirmation |
|---|---|---|
| New 2-go | Wooden two-story; one-story over 200 m²; etc. | Required (wall quantity, floor coefficient, connectors) |
| New 3-go | Small one-story wooden up to 200 m² | Skippable (similar to old 4-go) |
4. Concrete impact on wooden houses
The wall-quantity calculation, N-value calculation and floor-coefficient study used to be kept by the architect as design records. After the reform, they are submitted and reviewed at confirmation. The full set of structural-design rules (foundation, bearing-wall layout, connector hardware selection) is also reviewed.
5. Impact on schedule and cost
- Confirmation duration: from 1–2 weeks previously to 3–6 weeks after the change, depending on the reviewing body
- Design fee: trends upward roughly +5–15% from the extra structural-document workload
- Early coordination: the structural engineer should be engaged before the plan is fixed — not after
6. Existing homes, renovations and additions
Existing houses are not retroactively affected. Extensions and major renovations, however, may bring the work into "new 2-go" and trigger structural review. Existing-non-conforming buildings need an architect's assessment before any work, since the review scope depends on the building's current status.
7. Three things owners should know
- Add slack to the schedule: the confirmation adds 2–4 weeks. Land handover → groundbreaking → handover dates must absorb it.
- Lock the structural strategy early: "two-story or one-story", "what seismic grade" — settle these with the structural engineer during schematic design, not later.
- Seismic performance becomes visible: with structural documents reviewed by the authority, owners gain a third-party check on the seismic basis of their home — a real benefit.
The reform pushes architects, owners and the authority toward making seismic performance visible. The added time and cost are real, but the long-term effect is higher housing quality and stronger asset value. The key under the new rules: bring the structural engineer in early.