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During your build you may decide you want to substitute a component or product for a similar one.

You may want to do this based on price, lack of availability, or pressure from the building owner to use an alternative.

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

No matter how small these changes may appear, it is critical to clearly assess the impacts of potential changes to specified building systems and products. Especially so where they are ‘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 versus the intended performance level in your consented documents or under the building code.

Product suppliers and manufacturers are responsible under the Building Act for ensuring their products comply with the building code – assuming they are installed as per specifications. This means product manufacturers and suppliers should have documentation available to prove compliance claims.

If you are the builder, accepting verbal assurances on face value may potentially increase your exposure to liability in the future.

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”.

Therefore if you substitute, the buck stops with you.

In practical terms, if you choose to substitute a specified component then the responsibility lies with you to verify that the building system component is suitable for use (in all respects).

This means you should:

  • make sure it meets the required performance levels from the supplier (ie that the component performs the same as the original specification)
  • check with the building consent authority that they will accept the change
  • see if there are any implications around warranties provided by the original manufacturer or supplier of the specified system if you are switching components in specified building systems.

Managing your risk if you substitute products or materials

  • Check what materials/systems are specified on the approved consented plans and use them – as long as you follow manufacturer’s instruction, the responsibility for performance of the specified material(s)/systems is transferred to the designer(s)
  • If the product will be used in structural building work, check the manufacturer/supplier has provided evidence of 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 ‘x product or equivalent’ – then ensure that your choices of materials are supported by guarantees from a reputable supplier or manufacturer (preferably with 3rd party certification credentials)
  • Make sure your client is informed in writing of your choice of materials/systems – and send copies of material guarantees to them before doing the work.

Get it approved

If you or your client want to substitute a product – make sure you get this change approved by the building consent authority.

Depending on the product being substituted this could be either via a:

This way the information will be captured on file and become part of the approved consent documentation for the project – and provides you with better protection from potential claims in the future.

More information is also available on the MBIE website.

A product substitution guidance document aimed at BCAs, designers, contractors and building owners is available from the MBIE website.

More information on specific product substitutions