Framing and Structural Carpentry
Domain 3 tests timber framing to NZS 3604: choosing members from the tables, assembling walls and floors correctly, and protecting the bracing that keeps the building standing. Questions often give a span, a load width and a wind zone and ask for the right member or fixing.
Member selection
- NZS 3604 is the compliance path for timber-framed buildings; member size and grade come from its tables and depend on span, load width, wind zone and roof mass.
- SG8 is standard structural framing; a lintel must match the table for its load width - never "the same size as the old one".
- Match treatment to exposure: H1.2 for dry interior framing, H3.1 for exterior walls protected from weather, H4 or H5 where timber contacts the ground.
Assembly rules
- Studs at 600 or 400 centres, with trimmers and jack studs beside openings and dwangs to stop stud twist and support linings.
- Bottom plates are anchored at the spacings in NZS 3604 tables, with extra fixings at plate ends and bracing elements.
- Bracing elements are designed, not optional. Cut a service hole through a plywood or plasterboard bracing element and you have reduced the building's earthquake and wind resistance.
Worked example
A plumber wants a 100 mm waste through a floor joist near mid-span. Check the joist depth and the NZS 3604 limits on hole size, position and distance from edges. If the hole falls outside those limits, reroute the pipe or obtain specific design - do not drill and hope.
Traps that cost marks
- Notching the bottom (tension) edge of a joist or bearer.
- Cutting or altering trusses, or failing to brace them temporarily during erection.
- Removing dwangs to fit a pipe.
- Using nails where bolts or anchors are specified, or framing with untreated timber in a wet area.