Original roof cladding was generally corrugated iron. Most villas have been reroofed, also in iron.
Generally, short-run corrugated iron sheets, typically 8’ (2.4 m) long, were used in original installations, with heavy galvanising – 800 g/m2 (double that of current material). Galvanising was heavier on the exposed face than on the back face.
However, there are a number of villas, particularly in the more expensive suburbs, that were constructed with Marseille clay tile roofs (from 1901), with stone slate/shingles (slate was common in Otago where a source of good material existed) or occasionally with asbestos cement (from 1900).
Corrugated galvanised iron was available from the 1860s, imported from England in lengths from 5–10’ (1.5–3.0 m).
Material for use in New Zealand was nominally 26 (Birmingham) gauge – 0.18” (4.5 mm) – but in reality was 20% thinner than British standard. New Zealand manufacture started around 1886 but a significant amount was still imported. (Original iron may have been stamped on the back, identifying the manufacturer.) Also, the material was not consistent in depth or pitch as it was sourced from a number of individual manufacturers’ profiles.
Old iron roofing was rolled with eight symmetrical corrugations to give two corrugation side laps, but in New Zealand the material was laid with 1½ side laps, which meant alternate sheets had to be reversed. Given that back and front faces had different weights of galvanising, roofs were commonly seen where every second sheet was more corroded, even under a paint coating.
Galvanised iron ridging and hips were generally lead-edged to allow dressing to the profile. Flashings to complex junctions such as hip/ridge junctions, pipe and chimney penetrations and curved verandas were also done in lead. Some early flashings, if still remaining, may not have the lead edge.
Valleys were formed with galvanised iron flat sheet (see Figure 1), but there are instances of rolled lead being used.
Original barges were detailed using a flat timber cover board laid over the roofing, often replaced with galvanised iron barge roll or, in more recent reroofs, a folded flashing.
Tiles were often laid without tying to the structure. Where present, ties were vulnerable to corrosion.
Few villas are likely to remain with their original short length iron. Most would have been replaced with either later short-run iron or long-run corrugated iron fixed over underlay, most likely bitumen impregnated kraft paper.
Some examples of reroofing with metal tiles exist. Villas with clay tile roofs are likely to have the original roof intact.
Matching new cladding to original
Dimensions have changed for corrugated iron cladding, while matching clay roof tiles are unlikely to be available. There are several ways to deal with these problems. Read More.