Guidance on garage classification
The Department of Building and Housing has moved to clarify the classification of freestanding, uninhabited garages.
Classification of these garages had been ambiguous, as they are not explicitly mentioned under any importance level. The Department now considers that such garages should be classified as Importance Level 1 (low consequence of failure).
Building importance levels reflect the balance of a variety of factors, including consequences of failure and the cost of designing buildings to withstand applied loads. This guidance is issued under Compliance Document B1/VM1 and AS/NZS 1170: 2002.1
This Standard, like the previously referenced NZS 4203, differentiates buildings based on the risk that their failure would present to the safety of people, as well as any social, economic and environmental consequences that might arise.
The importance levels which express this differentiation include:
Level 1 (low consequence of failure)
This level is defined as low risk of loss of human life, and/or small or moderate economic, social or environmental consequences. It covers minor structures where their failure is not likely to endanger human life. Examples include structures smaller than 30m2, farm buildings, isolated structures, towers in rural situations, fences, masts, walls and in-ground swimming pools.
Level 2 (ordinary consequences of failure)
This level is defined as medium risk of loss of human life, or considerable economic, social or environmental consequences. Examples include single-family dwellings and car parking buildings.
After considering each of the criteria used to establish the importance level, the Department has concluded that the collective economic, social and environmental consequences of freestanding, uninhabited garage failure are lower than those of a dwelling.
The Department has considered the risk of loss of life in this context, recognising that, while cladding materials could be blown around in an inhabited area in very high winds, the level of risk is still low.
The Department considers that the low risk posed by the failure of these garages does not justify the added cost of constructing them to Importance Level 2.
Therefore, in the Department's view, freestanding, uninhabited garages should be classified as Importance Level 1 for the purpose of applied design loads.
1 This advice is issued as guidance under section 175 of the Building Act 2004. AS/NZS 1170 came into effect in December 2008 as a cited reference in the Compliance Document B1/VM1 Structure.