Tiled Roof Over a Sagging Purlin on a 1970s Brick Veneer
You are re-tiling a 1970s brick-veneer house in a coastal suburb. The existing terracotta tiles are removed and the battens are sound, but as you walk the roof you notice a 4 m section of the rear slope where the tiles sat noticeably lower than the surrounding plane. The rafter spacing is 450 mm, and the sagging section spans four rafters. The roof pitch is 22.5 degrees. The homeowner wants the new concrete tiles laid as soon as possible because rain is forecast in three days. The building surveyor has not yet inspected the stripped roof. Your supervisor is off site.
1. What should you do before laying any new tiles over the sagging section, and why?
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Stop and do not lay tiles over the sagging section. A visible dip in the tile plane after stripping usually indicates a structural issue - a deflected or broken rafter, a failed purlin, or a tie-down problem - rather than a tiling fault. Laying new concrete tiles, which are heavier than the terracotta being replaced, would add load to an already deflected member and could worsen the sag or create a safety hazard.
The correct sequence is:
- Barricade or mark the area and keep workers off it.
- Notify the supervisor and the builder in writing, describing the location, the 4 m span and the affected rafters.
- Wait for the building surveyor's inspection of the stripped roof, since the frame is now exposed and this is the point where defects are meant to be identified.
- Only proceed once the frame has been rectified and signed off, and confirm the new tile weight is within the roof's design capacity.
The three-day rain forecast is a scheduling concern, not a reason to cover a structural defect. Temporary weatherproofing (such as a secured tarp) can protect the interior without committing to the final tile lay.
2. The builder tells you the dip is 'just cosmetic' and asks you to pack it with mortar and lay the tiles. How do you respond, and what records do you keep?
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You should decline to conceal the defect with mortar packing. Packing a sagging plane with mortar does not restore structural capacity, can trap moisture, and hides a defect that the surveyor and future owners are entitled to know about. It may also breach your obligation to carry out work in accordance with the plans and relevant standards, and it could expose you to liability if the roof later fails.
Respond professionally: confirm in writing that you have identified a structural deflection, that you are not qualified to certify the frame, and that you will proceed once a rectification has been inspected. Keep:
- A dated written notice to the builder and supervisor.
- Photographs of the dip with a straight edge or string line across it.
- The surveyor's inspection outcome.
- Any written instruction you receive, and your response to it.
If the builder insists, escalate to your supervisor and, if necessary, the surveyor. Documenting the chain of instructions protects you and ensures the homeowner gets a compliant roof.