A stock shortage can trigger a product change, but availability is only the start of the assessment.
The specified product will not arrive in time. A supplier offers an alternative that is in stock and appears similar. The programme is under pressure, so ordering it immediately feels like the practical response.
Before doing so, separate the purchasing problem from the design and approval decision. The alternative may be suitable, but that needs to be established by the right people using the right information.
Put the comparison in one place
MBIE’s product-substitution guidance says a proposed replacement for a product in a building consent needs evidence of how it meets Building Code requirements. The building consent authority determines the appropriate consent process. Similar appearance or a supplier’s general reassurance is not the same as that assessment.
Give the designer a clear comparison: the specified item, the proposed replacement, the reason for the change and the supporting technical information. Identify related components and interfaces that may be affected. Avoid describing a product in isolation when it forms part of a system.
Client expectations also matter. Performance, appearance, maintenance and warranty arrangements can influence whether a substitution is acceptable commercially, even when compliance can be demonstrated.
Keep the two approvals distinct
A customer agreeing to a different colour or price does not itself resolve the consent implications. Equally, a technical assessment does not automatically authorise a change to the agreed contract price. Record the appropriate decisions separately and communicate them to the people ordering and installing the product.
Check whether the proposed change really protects the programme. Additional assessment, revised details or different installation requirements can reduce the apparent time saving. Make those steps visible before describing the substitution as a shortcut.
Once agreed and appropriately authorised, replace or clearly supersede the relevant instructions. The site team should not have to reconcile the original specification with a loose email while work is underway.
A useful substitution record explains why the change was made, who assessed it, what was approved and which documents now apply. It also provides the owner with a more accurate handover file. The immediate supply problem may be short-lived; the installed product will remain in the building much longer.