13.1 NZ Building Code Architecture: Clause G13, Clause E1 & Compliance Pathways

Building Code architecture and compliance pathways

The Building Act 2004 establishes the legal system, the Building Regulations contain the Building Code, and MBIE publishes compliance documents and guidance. Section 17 of the Act requires all building work to comply with the Building Code, even when the work is exempt from building consent. Consent status and code compliance are separate questions.

Performance-based Code

The Code states objectives, functional requirements, and performance criteria. For drainlayers, Clause G13 addresses foul water and Clause E1 addresses surface water. Other clauses may matter, including B1 Structure, B2 Durability, E2 External Moisture, G10 Piped Services, G14 Industrial Liquid Waste, and provisions for access and safety.

A performance requirement describes the outcome. It does not automatically supply a pipe size, grade, test, or material. The designer chooses a compliance path and assembles evidence that the proposed system meets the performance.

Acceptable Solutions and Verification Methods

An Acceptable Solution is a prescribed means of compliance. Work that falls within its scope and follows it completely must be accepted as complying with the covered Code provisions. A Verification Method is a prescribed test or calculation method. Scope and limitations are important: an industrial discharge excluded by G13/AS2 cannot be brought inside its scope merely by copying a pipe-size table.

G13/AS2 covers certain below-ground non-pressure foul drains up to DN150 and excludes industrial, chemical, or toxic liquid wastes needing pretreatment. G13/AS3 cites AS/NZS 3500.2:2021. These are separate paths. If AS3 is chosen, apply the cited standard and AS3 modifications. Do not combine the most convenient values from AS2 and AS/NZS 3500.2 and label the mixture an Acceptable Solution.

E1/AS1 provides prescriptive surface-water provisions within its scope. E1/VM1 provides calculation and test methods, including field soakage investigation and pipe leakage tests. Territorial-authority infrastructure requirements can add conditions for connection to a public network, but a local detail does not silently rewrite the national compliance document.

Alternative Solutions

A proposal outside an Acceptable Solution may be submitted as an Alternative Solution. Evidence can include engineering calculations, product appraisal, testing, comparison with compliance documents, expert opinion, and demonstrated performance. The BCA decides on reasonable grounds whether the proposal meets the Code.

“Specific engineering design” and producer statements can support that decision, but neither phrase is automatic approval. Define assumptions, design life, installation limits, inspection, commissioning, and maintenance. If site conditions change, review whether the evidence remains valid.

Versions and dates

The applicable consent and compliance-document versions matter. The examination guide states that legislation is examined as at 1 January of the examination year, while supplied compliance documents and standards are identified in the candidate material. On real work, use the versions applicable to the consent and transition provisions. Do not update one table in an approved design without reviewing the complete pathway.

Determinations

MBIE’s determination process resolves specified Building Act disputes and questions. A determination is a binding statutory decision for the matter, subject to the Act’s appeal route. It is not a court judgment and should not be described as a “judicial ruling.” Published determinations can be persuasive learning material, but facts and applicable document editions must be compared carefully.

Scenario

A designer uses the G13/AS2 access spacing, AS/NZS 3500.2 vent sizing, and a manufacturer’s unverified reduced gradient. That package has not followed one Acceptable Solution. It must be revised to one full pathway or presented as an Alternative Solution with evidence addressing every departure. The certifier should identify the issue before installation and obtain an approved amendment where required.

Independent source-check exercise

For 13.1 NZ Building Code Architecture: Clause G13, Clause E1 & Compliance Pathways, practise answering from evidence rather than recall. Write the controlling source, its edition or effective date, its scope, and the exact paragraph, table, figure, or manufacturer instruction that supports the decision. Then state the site inputs that can change the result. In this section those inputs include All building work must comply with the Building Code whether or not consent is required.; An Acceptable Solution is one way to establish compliance; an Alternative Solution may also comply when supported by adequate evidence.; G13/AS2 and G13/AS3 are distinct foul-water compliance paths and must not be mixed selectively..

Build a four-column check: proposed condition, source requirement, evidence observed, and action. Test the answer with one changed assumption. A different pipe size, discharge-unit load, ground condition, licence status, authority, compliance path, or consent condition may produce a different result. If it does, explain why; if it does not, show which requirement remains controlling.

Finish with a field-verification plan. Name what must be inspected before concealment, what instrument or record demonstrates it, who has authority to accept a change, and what appears on the as-built or completion file. This exercise turns an open-book fact into certifying-level judgement. It also exposes accidental mixing of standards: if the source for a dimension differs from the source for the test or approval, either return to one complete compliance path or document the proposal as an Alternative Solution. Do not promote an example value into a national rule.