A lot of the villas and bungalows around Gonville still have their original corrugated roofs, or a re-cover from decades back, and when the spouting finally gives up it is tempting to treat it as a simple swap: old gutter off, new one on, done in an afternoon. I have pulled enough failed replacement spouting off old Whanganui roofs to know that the pairing between an old roof and a new spouting system matters more than the brochure for the new product ever suggests, and most of the failures I see inside two or three years trace back to a mismatch nobody thought through at the time.
Roof pitch and catchment decide the size you actually need
A standard 115 mm or 150 mm spouting profile copes fine with most modest roof planes, but older Whanganui villas often have a long, low-pitch catchment feeding into a single run, and that changes the sums. The wider and lower the roof plane, the more litres per minute a given length of spouting has to carry in a heavy downpour, and a profile that was adequate for the smaller original roof can be undersized once an extension or a reroof has changed the catchment area feeding it. Sizing should be based on the actual square metres of roof draining to each downpipe, not on what was there before, especially on a river-flat section where storm events tend to arrive as short, intense bursts rather than steady rain.
What is usually rotten behind the old spouting
On houses built before the 1950s, the spouting typically hangs off a timber fascia board, and by the time the spouting itself is failing, that fascia has often been sitting wet at the back edge for years without anyone seeing it. I rarely take old spouting off a Gonville villa without finding at least a metre of soft or rotten fascia somewhere along the run, usually near a downpipe outlet or a valley where water sat longest. Fixing new spouting brackets into rotten timber is a false economy; the brackets pull free within a season or two, and the same job has to be done twice. Any quote for new spouting on an older roof should include an allowance to replace suspect fascia, typically $25 to $45 per linear metre for timber and labour, because that number is very hard to estimate accurately until the old spouting is actually off the wall.
Continuous runs against sectional lengths
Continuous spouting, rolled on site from a coil, has far fewer joints than sectional lengths bolted together every three metres, and fewer joints means fewer places for a leak to start ten years from now. On a long, straight run typical of a villa roofline, continuous is almost always worth the extra cost over sectional. Where continuous isn’t practical, such as around a complex hip roof with a lot of short runs and corners, sectional lengths with properly sealed and riveted joints are the more realistic choice, and the joint sealant is the part that needs checking every few years rather than the metal itself.
Mixing metals is where quiet corrosion starts
The failure I see most often on an older roof isn’t the new spouting itself, it’s what happens where the new spouting meets old fixings, old downpipes, or a roof that was never the same metal to begin with. Galvanised steel spouting fixed with the wrong fastener, or run hard against a copper downpipe left over from an earlier era, sets up galvanic corrosion that eats away at whichever metal is less noble in that pairing, usually the galvanised steel or aluminium. Colorsteel and aluminium products need to stay away from direct contact with copper or bare galvanised offcuts left in place from a previous job, and any dissimilar metal junction needs an isolating washer or a compatible transition fitting rather than a straight bolt-through connection. It is a slow failure, showing up as pitting and rust streaks two or three years after the new spouting went up, by which time it looks like a bad installation rather than the metallurgy problem it actually is.
Getting the sizing, the fascia condition and the metal compatibility right before a single bracket goes up is really a roofing decision as much as a spouting one, which is why on an older Whanganui roof it is worth having a Whanganui roofing contractor look at the roof and the spouting together rather than pricing the gutter as a stand-alone job.
Frequently asked questions
Can I fit new aluminium spouting straight onto an old galvanised steel roof? Not in direct contact; dissimilar metals in contact with running water set up galvanic corrosion, so the junction needs an isolating washer or a compatible transition fitting.
How do I know if the fascia board behind old spouting needs replacing? Soft or spongy timber, dark staining running down from behind the spouting, or brackets that have already pulled loose are the usual signs, and it is common on villas built before the 1950s.
Is continuous spouting worth the extra cost over sectional lengths? On a long straight roofline it usually is, because fewer joints means fewer places for a leak to develop over the next ten to fifteen years.