Many homeowners and developers who want to install poly water tanks on their properties face a common challenge: how to comply with the Building Code requirements for fire safety. The sticking point has been whether a plastic water tank sitting near a boundary is something the fire clauses were ever meant to catch. A determination from the Ministry of Business, Innovation and Employment (MBIE) has now answered that question, and the answer matters to anyone trying to fit a tank onto a tight site.
What Clauses C3.6 and C3.7 require
According to Clause C3.6 and C3.7 of the Building Code, buildings must have features that prevent fire from spreading to other properties or endangering people. This includes having a minimum distance between the building and the relevant boundary, or having fire-resistant construction or protection. The clauses are written about buildings. They exist so that a fire starting on one property does not become a fire on the next one, and the two routes offered, distance or protection, are alternatives rather than a checklist to satisfy in full. The question that arises on site is which structures the clauses actually apply to.
How the clauses were being applied to tanks
Some consenting authorities have interpreted these requirements to apply to poly water tanks as well, even if they are not part of the building structure. This means that some consenting officers would not allow a poly water tank to be installed within 1m of the boundary, arguing that it could pose a fire hazard or compromise the fire separation distance. The practical result was inconsistency. The same tank, on the same kind of site, could be accepted by one consenting officer and refused by another, depending entirely on how the clauses were read. If you are working through whether your tank needs a consent, this is where it tends to bite.
Why this hurts detention tanks most
This interpretation is particularly difficult for detention tanks in tight subdivisions where there is no space to set the tank 1m back from the boundary. A detention tank is rarely optional on those sites. It is usually the thing making the stormwater design work in the first place, and on a small section the boundary is where the space is. A 1m setback applied around a small site can remove the only viable tank position, which leaves the owner needing a tank they have nowhere to put. Slimline tanks on new builds run into the same geometry.
What an MBIE determination actually is
A determination is a legally binding decision made by MBIE on matters of doubt or dispute about the Building Code compliance of a specific building project. It is the formal way of resolving exactly this kind of disagreement, where the rule itself is not in dispute but its application to a particular thing on a particular site is. In this case a determination was applied for in relation to a site with a poly tank specified within 1m of the boundary, so the question put to MBIE was narrow and concrete rather than theoretical.
What MBIE determined
MBIE have released the determination and concluded the following:
"In accordance with section 188 of the Building Act 2004, I determine the stormwater tank near the boundary of the property is not required to comply with clauses C3.6 and C3.7 of Clause C3 Fire affecting areas beyond the fire source."
That is the operative wording, and it is worth reading exactly as written rather than as a summary. The tank was not found to comply with the clauses by some alternative route, and it was not granted an exemption from them. It was found not to be required to comply with them.
What this means in practice
This means that poly water tanks can be installed directly on a boundary without a setback, without consent issues going forward. MBIE found that the risk of fire spread from a poly water tank to another property is very low, and that the tank does not form part of the building envelope or affect the fire separation distance. MBIE also noted that the tank is designed to withstand the effects of weathering and UV radiation, and that it has a self-venting lid that would release any pressure build-up in case of fire. The determination sets a precedent for future applications involving poly water tanks near boundaries, and provides clarity and consistency for homeowners, developers and consenting authorities. It sits alongside the wider question of whether poly water tanks are safe.
The limit: council planning rules still apply
This determination is specifically in relation to building consent. Some local councils may have a unitary plan requirement for the tank to have a setback due to aesthetic reasons. This determination does not override local council planning rules, and is specifically in relation to the Building Code clause. Those are two different instruments, and clearing one does not clear the other. Before you site a tank hard against a boundary, check the district or unitary plan as well as the Building Code, because a planning setback imposed for appearance is untouched by anything MBIE has determined about fire.
Where this leaves your tank
For anyone weighing up a poly tank on a constrained site, the determination removes one specific obstacle: the fire clause argument against a tank within 1m of a boundary. It also supports the use of water tanks as a sustainable and efficient way of managing stormwater runoff and reducing the demand on the public water supply. If you are a Promax customer looking to install a poly water tank on your boundary, talk to our team about the tank and the site together.