5, 15 or 50 years: B2 durability waterproofing explained

“How long should it last?” is one of the first things homeowners ask us. The Building Code has its own answer, and it isn’t one number. B2 durability waterproofing rules set minimum lives of 5, 15 or 50 years depending on how hard a part of the building is to reach and replace, and how easily a failure would be noticed. Here’s what that means for the waterproofing in your home.

What clause B2 actually says

Clause B2 is part of the Building Code in Schedule 1 of the Building Regulations 1992. We checked the wording on the official New Zealand Legislation website. Clause B2.3.1 says building elements must, with only normal maintenance, keep meeting the Code for the specified intended life of the building, if one is stated, or for:

• The life of the building, being not less than 50 years, if the element gives the building structural stability, is difficult to access or replace, or would fail without anyone noticing during normal use and maintenance.
• 15 years, if the element, such as the building envelope, is moderately difficult to access or replace, or a failure would go unnoticed in normal use but be easily found during normal maintenance.
• 5 years, if the element, such as services, linings, renewable protective coatings and fixtures, is easy to access and replace, and a failure would be easily noticed in normal use.

The clock starts when the code compliance certificate is issued. For a non-consented small stand-alone dwelling, such as a granny flat built under the exemption, it starts when the building work is completed.

Where common waterproofing sits

The Code doesn’t give a table of products. It sets the tests, and the designer, the manufacturer’s documentation and the building consent authority work out which period applies to each element. As a homeowner, a useful way to think about it is to ask the same questions the clause asks.

Tanking behind basement and retaining walls

Tanking on the outside of a buried wall is about as hard to reach as waterproofing gets, and a failure might not show for a long time. That points towards the 50-year end of the scale. Our below-ground waterproofing post covers this in more detail.

Membranes under tiles

A shower or balcony membrane under tiles can’t be reached without lifting the tiles. How a particular system is assessed depends on the design and documentation, so ask your waterproofer what durability the system is documented for.

Exposed deck and roof membranes

An exposed membrane on a deck or flat roof is part of the building envelope and can be inspected and maintained. Topcoats and protective coatings that are designed to be renewed are a different case from the membrane itself.

Why “normal maintenance” matters

Every B2 period assumes normal maintenance. For a deck or roof, that means keeping outlets clear, keeping pot plants and furniture from damaging the surface, and renewing coatings when the manufacturer says to. A membrane that’s never looked after won’t be judged the same way as one that has been.

Code durability and warranties are different things

B2 is a minimum performance requirement under the Building Code. A warranty is a promise from a manufacturer or installer, with its own terms. They don’t measure the same thing, so don’t read one as the other.

For example, we use ARDEX WPM 300 HydrEpoxy for basement waterproofing, applied to the inside (negative side) of the wall. On HydrEpoxy jobs, ARDEX gives a 10-year product warranty, and Auckland Waterproofing Experts gives a separate 5-year workmanship warranty. Those warranties are a separate thing from the Building Code durability periods.

How Auckland Waterproofing Experts approaches durability

We choose systems with manufacturer documentation for the job, prepare the substrate properly, follow the manufacturer’s instructions and photograph each stage. That gives you, your designer and the council a clear record of what was installed. See our waterproofing membranes page and our guide to waterproofing retaining walls.

Questions we get about B2 durability

Does the 50-year period mean my membrane will last 50 years?

No. It is the minimum the Code requires for that type of element, assuming normal maintenance. Real-world life depends on design, installation, exposure and upkeep.

Is a warranty the same as Code durability?

No. A warranty is a separate promise with its own terms. Code durability is a legal minimum performance requirement.

Where can I read clause B2?

The full wording is in Schedule 1 of the Building Regulations 1992 on the New Zealand Legislation website.

Want waterproofing that’s built to the right standard?

Talk to us about your basement, deck, roof or bathroom. Call us at Auckland Waterproofing Experts on 022 630 6434 for a free site visit. We’ll explain what we find in plain English and send you an itemised quote. You can also read our waterproofing FAQs.

Email aucklandwaterproofing@gmail.com. We’re available 7am to 7pm, Monday to Saturday, based in Castor Bay and working across Auckland and the North Shore.