Product substitution in building systems

Your reasons for wanting to substitute may be valid, but when the product is part of a building system it can have much wider implications.

Probably one of the most common questions received by product manufacturers, suppliers and Building Authorities is “can I substitute a component or product in the specified system for a similar one”. Often price, lack of availability or pressure from the building owner to use an alternative are cited as reasons for wanting to deviate from the specified component.

The Building Act

With the recent amendments to the Building Act it is more critical than ever for builders to clearly assess the impact of potential changes to specified building systems no matter how small these may appear. This is especially true for ‘critical’ building systems such as structural bracing, fire and noise control. Even switching out small components such as fasteners, sealants or adhesives may impact the level of system performance achieved verses the intended performance level in the consented plan or required under the NZ Building Code.

As part of the recent amendments to the Building Act, product suppliers and manufacturers are now responsible for ensuring their products (assuming they are installed as per specifications) comply with the NZ Building Code. For builders, this means product manufacturers and suppliers should have documentation available to prove compliance claims. Accepting verbal assurances on face value may potentially increase the builder’s exposure to liability in the future.

It is more critical than ever for builders to clearly assess the impact of potential changes to specified building systems no matter how small.

As Winstone Wallboards puts it “GIB® plasterboard systems are regularly tested and use specifically named products. This ensures GIB® systems can provide known levels of performance which specifiers and builders can rely on. Unfortunately it’s simply not possible to test all the combinations of products on the market”.

If you substitute, the buck stops with you

In practical terms, if you choose to substitute a component in a specified building system then the responsibility lies with you to verify that the building system component is suitable for use (in all respects). This means not only making sure it meets the required performance levels from the supplier (that the component performs the same as the original specification) but you may also need to check with the local building authority that they will accept the change. Additionally, switching components in specified building systems may also have implications around system warranties provided by the original manufacturer or supplier of the specified system.

Managing your risk

So you well may ask “I’m a tradesman, not an engineer or materials scientist. How do I partially manage my risk around the materials used in specified systems and more generally as part of the wider project?”

  • Firstly check what materials/systems are specified on the consented plans and use them. The responsibility for performance of the specified material(s)/systems is transferred to the designer (as long as you follow manufacturer’s instructions).
  • If the product will be used in structural building work, check the manufacturer/ supplier has provided evidence of NZ Building Code compliance and that the proposed use is within scope.
  • If interior materials are not specified or the consented plans contain words such as ‘ABC product or equivalent’ then the wise tradesperson would ensure that his choices of materials are supported by Guarantees from a reputable supplier or manufacturer (preferably with 3rd party certification credentials). Also make sure your client is informed in writing of your choice of materials/systems and remember to send copies of material guarantees to them prior to commencing work.