Signs a downpipe is in trouble
The classic sign is spouting overflowing near an outlet while the downpipe below barely trickles. That's a blockage, usually at the top where leaves collect, or at the first bend.
Others are water spraying from a joint in rain, a pipe leaning off the wall because its brackets have let go, cracked or chalky PVC, rust at the base of a metal pipe, and puddles or gurgling where it meets the drain. Dimond recommends three brackets per downpipe, so one hanging on a single bracket is overdue for attention.
If clean spouting still overflows at the same spot every heavy rain, there may be too few downpipes, or outlets too small, for the roof area draining to them.
What New Zealand downpipes are made of
| Sizes and shapes | Worth knowing | |
|---|---|---|
| PVC | Marley's RP80 is 80mm round | If painted, light colours only, Marley says, or the pipe can move and leak |
| Coated or pre-painted steel | Dimond's standard is 80mm round in 3.2m lengths, in ColorCote MagnaFlow or Zincalume | Roofing Industries says downpipes must be compatible with the roof and spouting material |
| Larger or rectangular | Metalcraft makes round 80mm, 100mm and 150mm, plus a 55x75mm rectangular pipe | A bigger pipe takes more water where a large roof area drains to one point |
| Copper | Available from Dimond | Dimond says zinc elbows must not be used with copper, and NZ Steel says water off copper shouldn't reach coated steel |
Downpipes inside walls, and flat-roof outlets
Dimond doesn't recommend running its downpipes through wall or ceiling cavities. When one leaks or blocks in there, the water is inside the house before anyone sees it, and the NZMRM Code of Practice notes the Building Code expects internal gutters and downpipes to last fifteen years, against five for external gutters.
Flat roofs, minimal eaves and complex roof shapes were common on the 'Mediterranean' style homes caught up in the leaky homes crisis, and a flat roof often drains through outlets rather than straight into spouting. E2/AS1 asks for a membrane roof outlet at least 75 mm across, with an overflow or a second outlet. If your flat roof has one outlet and no overflow, get it looked at before the next big rain. Our membrane roofing page covers those roofs.
Where the water goes next
In town, downpipes usually drain to the stormwater system. If water backs up and spurts from the lowest joint, the blockage is often below ground, which is a drainlayer's job rather than a roofer's. A downpipe that just empties beside the house puts water against the foundations, where you least want it.
On tank water, the downpipes feed the tank, and a first-flush device that sends the first dirty water away is worth having. New Zealand Steel says the first 25 mm of rain off a newly installed ZINCALUME roof must be discarded before collecting drinking water. Before the roof is painted, disconnect the tank: Resene says downpipes should stay off until after the first shower of rain on fresh Summit Roof, and Wattyl asks for at least 10 to 15mm of rain first.
Volcanic ash is the other New Zealand case. Auckland and Taranaki emergency management both advise disconnecting downpipes from the spouting and disconnecting rainwater tanks if ash is coming, so it pays to know now how yours come apart.
Old downpipes and ladders
WorkSafe lists downpipes and spouting among the places asbestos can turn up in homes built before 2000, and you can't tell by looking. Don't cut, drill or water-blast an old grey cement downpipe until it's been tested. Clear blockages from the bottom, standing on the ground. Rodding a downpipe from the top means working at spouting height, so leave that to someone with proper access.
What a good downpipe job includes
- Pipe material matched to the spouting and roof, with no copper draining onto coated steel
- The number and size of downpipes explained for your roof area
- Brackets at the maker's spacing, which for Dimond means three per downpipe
- An overflow outlet, so a blockage spills somewhere harmless
- The connection to the drain sealed and tested with a hose
- No new pipes run inside wall or ceiling cavities
- Old pipes taken away, with a plan if they turn out to be asbestos cement
What you can do, and what's for a roofer
You can
- Clearing the bottom outlet by hand or with a hose, from the ground
- Emptying leaf diverters or filters at ground level
- Noting which downpipe struggles in heavy rain
- Checking water runs away from the house
- Knowing how your downpipes disconnect from the tank
Leave to a roofer
- Blockages at the top or inside walls
- Re-bracketing and replacing lengths
- Adding downpipes, outlets or overflows
- Asbestos cement downpipes
What we'd do about a struggling downpipe
We'd try clearing it from the bottom first. If it blocks again within months, we'd look up at the trees and the spouting cleaning routine, because the downpipe is usually just where the problem shows. If clean spouting overflows at one spot in every downpour, we'd ask a roofer about another downpipe or a bigger outlet before anything else. A downpipe inside the house, or a flat-roof outlet with no overflow, we'd get checked soon.
Want a roofer to take a look?
Tell us the job and your postcode. We match it with a Find My Roofer certified roofer who specialises in that kind of work, and they call you to quote. Your number goes to them alone.