Materials, Tools and Equipment
Domain 6 tests material selection by exposure and structural role, fixing corrosion, and safe, correct use of the tools that dominate a building site. Expect questions matching a treatment class to a location, or a fixing to a corrosion zone.
Timber and treatment
- Treatment class pairs with exposure: H1.2 for dry interior, H3.1 for exterior protected above ground, H3.2 for exposed above ground, H4 and H5 for ground contact, H6 for marine.
- Cut ends, notches and drilled holes in treated timber need re-treatment with an approved preservative.
- Engineered products - LVL, glulam, I-joists - have their own span tables and manufacturer restrictions on cutting and drilling.
Fixings and corrosion
- The NZS 3604 corrosion zones drive fixing choice: standard galvanised inland, hot-dip galvanised or stainless near the coast and in geothermal areas.
- CCA-treated timber is corrosive to steel; use stainless or heavily coated fixings and a damp-proof course between timber and concrete or steel.
Tools and equipment
Keep blades sharp and guards working; clamp material in the drop saw; use framing nailers with the sequential trigger on site; powder-actuated tools only by trained operators. Electrical tools need current test-and-tag. Cutting fibre cement or concrete requires dust extraction or wet cutting plus a suitable respirator.
Worked example
A deck bearer in ground contact near the coast. Ground contact requires H5 treatment; salt exposure pushes the fixings to stainless steel; and where the bearer bears on a concrete pile, a DPC separates timber from concrete so moisture is not drawn into the timber.
Traps that cost marks
- H3.1 timber used in ground contact.
- Untreated cut ends left exposed.
- Galvanised nails driven into wet CCA timber.
- The wrong blade for the material, or a nail gun bumped rather than triggered.