NZS 3604: Lintels, and Importance Levels
Practical experience suggests that where sliding doors are concerned, the lintel deflections under NZS3604 sizings are problematic. Just as NZS3604 floor joist sizings are perhaps going to give unwelcome “bounce”, we suggest that where there is a prospect that a sagging lintel may lead to a jammed slider, you would do well to consider a steel lintel or flitch beam and perhaps with a pre-camber. If shims were provided at installation to take up expected deflection, make sure they are removed to allow for that later deflection to happen!
All public buildings – including simple single storied buildings such as classrooms, libraries and public halls – are designated under NZS 1170.5 as having a BUILDING IMPORTANCE LEVEL (BIL). Most public buildings have an BIL of 3 or greater, and NZS 3604:2014 does not apply to buildings which have an BIL of 3 or greater: so all timber framing will need to be specified by a Structural Engineer as a Specific Engineered Design (SED).