A new patio or carport roof catches all the rain that used to soak into the lawn. In a South East Queensland summer storm that is a lot of water in a short time. Where it goes is part of the design, and getting it wrong shows up fast: water against the house, a soggy corner of the yard or an unhappy neighbour.
How much water?
Every millimetre of rain on a square metre of roof is a litre of water. A 6 × 4 m patio is 24 m², so 50 mm of rain in a storm puts about 1,200 litres off that roof. A double carport sheds about the same again. The gutters and downpipes have to carry it at the peak of the storm, not just on average.
Where it can go
- Into your existing stormwater line, which runs to the street kerb or a council drain. This is the usual answer.
- Into a rainwater tank, with the tank overflow connected to stormwater.
- In some cases on larger lots, to a dispersal point well away from buildings and boundaries, if the council and certifier accept it.
What it cannot do is run onto a neighbour’s land or pool against your house slab. Queensland calls the accepted outlet a lawful point of discharge, and the building approval checks it.
Who connects it
The gutters and downpipes come with the patio. Connecting a downpipe into the underground stormwater is plumbing and drainage work for a licensed plumber. We tell you before the build where the downpipes will land, so it can be booked for the same week.
Gutter size and placement
- Gutters and downpipes are sized for the roof area and South East Queensland rainfall. A long patio may need a downpipe at each end.
- The gutter goes on the low side of the roof, with enough fall to the downpipes.
- Close to a boundary, the gutter keeps the water on your side.
- Gutters near trees need a leaf guard or more frequent cleaning.
The flyover gap
A flyover patio sits above the house gutter, which keeps that gutter open and easy to reach. It also means two gutters: the house gutter under the gap and the patio gutter at the outer edge. Both need to drain. Leaves that blow into the gap end up in the house gutter, so check it with the patio one.
Attached under the eave
An attached patio fixed under the house gutter often has its own gutter at the outer edge and drains away from the house. If a design drains back towards the house, the house gutter and downpipe have to be big enough for both roofs. We check that rather than assume it.
Council pipes in the yard
Many yards have a council stormwater main or an easement running through them. Footings near a council stormwater pipe are assessed under the Queensland Development Code: about 1.2 m from a pipe up to 375 mm, and 3 m from a larger one. If a post must go closer, it becomes a referral to the owner of the pipe, which in Brisbane is council, with a 2026-27 fee of $900.
Keeping it working
- Clean the gutters at least twice a year, and before storm season.
- Check downpipe joints and the connection at the ground after big storms.
- Hose out the outlets if water overflows the gutter in moderate rain.
- Keep mulch and soil away from where the downpipe meets the ground.
- Watch for staining down the posts, which often means a blocked outlet.
Signs of a problem
Water spilling over the front of the gutter in an ordinary shower, puddles forming under the roof, or water running towards the house all point to a blocked or undersized gutter or downpipe. Clear it first. If it keeps happening, the design may need another downpipe.
In our quotes
Every patio and carport we quote includes gutters and downpipes sized for the roof, and the plans show where the water goes. If you would like the water to go to a tank, tell us at the measure-up and we plan the downpipes to suit.
Rainwater tanks
A patio or carport roof is a good catchment for a tank, because it is often close to the garden. The downpipe runs to the tank, and the tank overflow connects to stormwater so heavy rain still has somewhere lawful to go. Tell us the tank position early, as it changes where the downpipes go.