Our 1926 bungalow came with a concrete tile roof that somebody had put on in the late 1970s, over rafters that were never designed for it. You could see the result from the street once you knew to look: a ridge line with a gentle dip in the middle, like a hammock. Three roofers came through. Two quoted tile for tile. The third put a level on the ridge, went into the roof space with a torch, and came back out asking whether we had ever had the framing looked at. That conversation cost us an extra fortnight and saved us a structural problem.
The weight difference is the whole argument
Concrete tile weighs in the order of 45 to 55 kilograms per square metre installed. Long-run coated steel is around 5 to 6. On a 140 square metre roof that is a difference of roughly six tonnes sitting on framing that, in a 1920s bungalow, was originally sized for corrugated iron and maybe a shingle underlay.
Going from tile to steel therefore removes load, which is almost always structurally welcome and is one of the reasons older houses that were re-roofed in tile are so often re-roofed back to steel a generation later. Going the other way — steel to tile on an old bungalow — needs the framing assessed, and often needs new purlins, battens or additional support. Anyone who quotes tile on a 1920s house without going into the roof space is guessing.
Noise, condensation and the things you live with
The standard objection to steel is rain noise, and it is real but overstated. A modern long-run roof over a well-insulated ceiling with a proper underlay is not loud in a habitable room; it is loud in a lean-to with a lined ceiling and no insulation. Tile is quieter under heavy rain by a noticeable margin, which matters more if you have a room in the roof.
Condensation is the reverse trade. Steel is a cold surface and moist air from the house will condense on its underside if the roof space is not ventilated and the underlay is not doing its job. A tile roof breathes through the laps almost by accident. A steel roof needs the underlay, the ventilation and the ceiling insulation treated as one system — this is the single most common defect I see on re-roofs done cheaply.
Three budgets, not one
People compare the roofing material and ignore two other lines that often decide the job.
- Materials and install. Long-run coated steel on a straightforward bungalow roof commonly runs somewhere around $120 to $190 per square metre installed. Concrete tile is broadly comparable, often $110 to $170, with pressed metal tile sitting above both.
- Strip-out and disposal. Removing six tonnes of old concrete tile is a skip-and-labour exercise that can add several thousand dollars. Old corrugated iron is lighter and, if it predates the 1980s, may need testing before it goes anywhere.
- Everything that gets exposed. Rotten fascia, undersized purlins, missing dwangs, a chimney that needs flashing properly for the first time in a century. On a bungalow, budget 10 to 20 per cent contingency for what the strip-out reveals.
Lifespan in a West Auckland setting
Under the bush canopy in the foothills the pressures are different from the coast. Leaf litter and constant shade keep the roof damp and encourage lichen, which sits on the surface and holds moisture against the coating. Salt is a factor closer to the harbour but is not the dominant one inland. A quality coated steel roof kept clear and washed should give 30 to 45 years; concrete tile can outlast that structurally while needing the surface coating redone every 15 to 20 years and the ridge bedding checked far sooner than most people do.
We went with long-run steel in the end, partly for the weight and partly because the profile suited a 1920s roofline better than the tile ever had. We used the team that handled ours on the strength of the one thing the other two did not do, which was look at the framing before quoting the covering.
Frequently asked questions
Does re-roofing need building consent? Replacing a roof with a comparable material generally falls within the exemptions, but changing material type, changing the roof pitch, or work that alters the structure can require consent. Confirm with the council before the scaffold goes up, not after.
Can I re-roof over the existing tiles? Battening over tile is done, and it hides everything you most need to see. On an older bungalow the strip-out is where the structural problems surface, which is the main reason to do it.
How long does a bungalow re-roof take? Typically five to ten working days for a straightforward 140 square metre roof, plus scaffold up and down. Rain days are the variable; a good contractor will only strip what can be closed in the same day.