Pre-line walk reveals a suspect lintel, a notched I-joist and missing bracing
Framing is up on a single-storey 180 m² house in Tauranga and the pre-line inspection is booked for Friday. On your walk you find three things. First, a 4.2 m wide opening between the living area and a covered portico in an external wall carrying a tiled roof; the lintel installed is a single 190x45 SG8 with about 60 mm of bearing at each end, and the load width above it is roughly 1.8 m. Second, a 240 mm deep engineered I-joist in the floor has a 45 mm deep notch cut into its top flange where a plumber ran a 40 mm waste pipe, about 800 mm from a bearer. Third, two diagonal bracing elements shown on the bracing plan in the north wall have been removed to fit a 2.4 m wide sliding door and nothing has replaced them. The builder says the engineer 'over-designed it' and that the bracing plan is only a guide.
1. For each of the three items, state whether it complies, the technical basis, and the consequence if it is left.
Read the worked answer
Lintel. The span, load width and roof type must be read off the NZS 3604 lintel tables (or a specific design). A 4.2 m span with about 1.8 m of load width under a heavy tiled roof is well beyond what a single 190x45 SG8 will carry - you would normally be looking at a 240x45, a built-up member or an engineered beam. Bearing is also wrong: NZS 3604 expects a minimum 90 mm bearing at each end of a lintel unless specifically designed otherwise, so 60 mm concentrates load and risks crushing and splitting at the support. Left in place: excessive deflection, cracked linings, a bouncing floor line, and a structural element that does not comply with B1. This is a fail at inspection.
I-joist. Engineered I-joists are proprietary, and the manufacturer's span and hole charts are the compliance path behind their producer statement. The flanges carry the bending forces; a 45 mm notch in the top flange cuts the compression chord and creates a stress concentration at exactly the point of highest moment near the bearer. Flange notching is prohibited. Holes are permitted only in the web, within the chart's size and location limits, including minimum distance from bearings. Left in place: a sagging floor, squeaks, and a floor that cannot be signed off.
Bracing. The bracing plan is part of the consented documentation and NZS 3604 requires bracing demand to be matched by bracing capacity on each line and each level, with continuity through to the foundation. Removing two elements for a 2.4 m slider reduces capacity on that line without reducing demand. 'Over-designed' is not a call a builder can make. Left in place: a house that may rack under wind or earthquake load, and a failed inspection.
2. What do you tell the builder, and how do you sequence the fixes so Friday's inspection is not wasted?
Read the worked answer
Tell the builder in writing, on the day, and take control of the inspection booking.
- State the three items, their locations, and that no linings are to be installed until each is resolved. Photograph each defect with a location tag and record it in the site diary.
- Raise an RFI to the designer for the lintel (correct member and bearing detail) and for the bracing (relocated or alternative bracing to restore capacity). Contact the I-joist supplier or engineer for a repair detail - options are typically a proprietary plywood side-plate repair fixed to their specification, or replacement of the joist. A nailed-on patch is not a repair.
- Reroute the 40 mm waste pipe rather than keeping the notch - through the web at an allowed location, or below the joist in a small bulkhead.
- Rebook or postpone the pre-line inspection. Letting the inspector find these wastes everyone's day, and the council can issue a notice to fix under the Building Act 2004 for work that does not comply with the consent - which stays on the property file and delays the Code Compliance Certificate.
- Order the replacement lintel and joist immediately and tell the client what has happened, why the lining date moves, and who carries the cost. Replacement of a framing member found before lining is cheap; the same defect found after lining is a demolition job.
- Re-inspect and photograph each fix before the linings go on, and record the designer's written confirmation with the consent documents.
3. After the bracing is changed, how would you demonstrate that the wall line is still adequately braced?
Read the worked answer
By doing the numbers again against the standard, not by judgement.
The process:
- Establish the bracing demand for the line from NZS 3604 using the wind zone for the site, the roof type and pitch, the storey height, the cladding weight and the subfloor type. Demand is not a single number for the house - it is calculated per line and per level.
- Establish the capacity of each remaining bracing element from the manufacturer's published ratings or the section 5 tables: sheet bracing (plywood or gypsum bracing systems with their fixing schedule), metal angle bracing, or a rigid air barrier system. Capacity depends on the fixing pattern, sheet size and edge distances, so the installed pattern must match the rating being claimed.
- Sum the capacities along the line and compare with demand. If the two removed diagonals leave a shortfall, the designer relocates bracing - for example into the wall returns either side of the slider, into an adjacent wall on the same line, or by upgrading the remaining elements to a higher-rated system.
- Check continuity: bracing must transfer load down through the dwangs, the bottom plate fixings and the subfloor bracing to the foundation. Adding a sheet at the top of a discontinuous line achieves nothing.
- Record the calculation on the bracing plan, have the designer issue the amended plan, and confirm with the council whether the change sits inside the consented scope or needs an amendment. Then keep the signed plan and photos on site for the inspector.