Designers get specific with specs

This Issue This is a part of the Product substitution feature

By - , Build 113

Builders are not designers and yet, for many reasons, they are often making product and detail decisions on site. One answer is for designers to provide more detailed, clear design specifications.

The quality of building consent documentation provided by designers has improved over recent years, with the increase in Building Code and standards compliance requirements and a more rigorous consenting process.

However, designers are still not always clearly specifying the product they want used in a particular situation. Notations on drawings are often non-specific, such as ‘expanding foam air seal’, ‘selected wall underlay’ and ‘continuous protective sealant’. The builder is left to decide what actual product to use, but really they should ask the designer for more information.

Often the notation ‘or similar’ is attached to specified components. Again, this allows the builder to change from the specified product, but has implications contractually and in terms of final Code compliance.

The devil is in the detail

It is the designers’ responsibility to ensure that buildings they design comply with the Building Code and relevant standards. The building needs to be fit for purpose and meet clients’ design and performance expectations. To do this, the designer needs to clearly specify all components that are to be used in construction.

The designer must nominate actual products, not generic product types. They should have the expert knowledge of different products’ performance and suitability to be able to specify those they believe will provide the level of performance required for each situation. This is particularly important for the weathertightness, durability and structural performance of a building, and to ensure a healthy safe environment for occupants.

Concise and specific documentation will also allow the builder to provide an accurate price and, ultimately, contract to construct exactly what the designer has specified, what has been consented and what the client is paying for. It should also speed up the consent process.

Assists building consent process

Detailed consent documentation provides the Building Consent Authority (BCA) with sufficient information to accurately assess the proposed building at the building consent stage and ensures that the building, if built in line with the consented documentation, will be Code compliant.

BCAs should have a comprehensive building consent process in place to identify any shortfalls in product specification. However, accurate assessment does not always occur, and documents that are not entirely specific are often consented when they shouldn’t have been.

Product substitution and builders

Product substitution is quite common in New Zealand construction and is often unauthorised. Sometimes, it may be unavoidable due to unavailability or delays in supply of the specified product. While substitution often results from non-specific documentation, it can also arise due to the:

  • builder’s preferences for other similar products due to cost
  • builder’s desire to use a preferred supplier or subtrade
  • builder not being comfortable using the specified product, for example, they may believe it is not fit for purpose
  • owner changing their mind.

Liability issues

The designer, in consultation with their client, should always make product substitution decisions. If the builder has concerns, they should consult the designer.

If the builder makes substitutions without approval, they may no longer be constructing the building they have contracted to provide or that has been consented, which has potential legal and liability issues. This is particularly important where decisions affect compliance, as it is the designer’s responsibility (as the owner’s agent) to ensure that the completed building will be compliant.

BCA may require new building consent

The BCA also needs to be made aware of product substitution, and in most cases, an amendment to the building consent will be necessary.

With minor substitutions, most BCAs allow the on-site building inspector to decide whether or not to approve the change. Approval is noted on the consent documentation and the building consent file. This generally applies to substitutions where compliance with Building Code performance requirements is maintained.

Where substitution is minor but results in a lower level of performance, the BCA may require the designer to lodge a formal amendment to the building consent to allow them to assess the revised performance and confirm that it still meets Code requirements.

Major product substitution will require a formal building consent amendment to be lodged, and in situations relating to major variations, a new building consent will often be required.

If the BCA is not made aware of product substitutions during construction, the building could potentially be assessed as non-complying at the completion stage, and this may result in the non-issue of a Code Compliance Certificate.

Strive for high-standard documents

Clear and specific building consent documentation allows the BCA to assess compliance accurately and for the builder to construct exactly what the designer and their client require. Designers should therefore be striving to provide a high standard of documentation that ensures the completed building is both compliant and fit for purpose.

For more

The Guide to building consent amendments can be downloaded free from www.dbh.govt.nz/UserFiles/File/Publications/Building/Guidance-information/pdf/guide-to-amendmnts-sept-08.pdf

Download the PDF

More articles about these topics

Articles are correct at the time of publication but may have since become outdated.

Advertisement

Advertisement