Posted: 5 June 2018
The building consent authority (BCA) received a building consent application for a new gym and learning centre for a school.
The proposal included two different designs for door thresholds – one level and one with a 20 mm change in level. Out of the six entrances, three entrances were to include the 20 mm change in level and three entrances were to be level. The level entrances included the main entry to the gym and were all underneath a canopy. The other three entrances were not covered by a canopy and were designed to have a 20 mm change in level to prevent water entering.
Issues arose between the BCA and the designer regarding the door threshold design with the 20 mm change in level. The BCA believed the 20 mm change in level did not comply with the accessibility requirements of Clause D1 or escape route requirements of Clause C4. The BCA believed the building could be designed so the change in level wasn't required.
The determination considered compliance of this door threshold design with Clauses D1 Access Routes, C4 Movement to a place of safety, and E2 External moisture. It noted the BCA had incorrectly tested the design against its own view of best practice for accessible entranceways, rather than the relevant performance requirements of the Building Code. Building work is not required to achieve performance criteria additional to the criteria prescribed in the Building Code (refer section 18(1) of the Act).
The determination assessed the door threshold design against relevant Acceptable Solutions. Under section 19, Acceptable Solutions are deemed to comply with the Building Code. A BCA must accept a design as compliant when it satisfies an Acceptable Solution.
The three entrances containing the 20 mm level change weren’t required to be accessible, meaning D1/AS1 was the applicable Acceptable Solution. D1/AS1 allows for 'threshold weather stops' provided they are 20 mm or less in height, although it acknowledges height changes at entrances are inconvenient for wheelchair users.
The determination considered the term ‘weather stop’ as used in both D1/AS1 and NZS 4121, 'stepped thresholds' as used in NZS 4121 and 'isolated step' as used in D1/AS1.
The determination considers a weather stop to be a building element that is raised above the level of the outside surface to stop water entering the building. Weather stops are often included in the design of doorsets, projecting above adjacent surfaces, and only used in regard to external doors.
In NZS4121, a stepped threshold is considered as a change in level where one side of a threshold is higher than the other. In D1/AS1 an isolated step is used to describe a change of level.
The determination took the view that D1/AS1 doesn't stop the use of a stepped threshold from being incorporated into the design of a weather stop.
The use of a stepped threshold or projection to prevent water entering a building will have an impact on accessibility. However, NZS 4121 and D1/AS1 acknowledge this, and allow a 20 mm change in level as it will still provide an adequate accessible entrance.
The door threshold design satisfied D1/AS1 and therefore was deemed to comply with Clause D1. The determination also found the design satisfied C/AS1 and E2/AS1.
The design satisfied D1/AS1, C/AS4, and E2/AS1 and therefore complied with the Building Code.
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