Salmon Plumbing Guarantee to ARRIVE ON TIME to your scheduled appointment.
In the rare instance that your plumber has been delayed due to unforeseen circumstances beyond our control, we promise to give you a MINIMUM 30-minutes notice of ANY change in arrival time and will offer to reschedule, if that’s more convenient for you
If we don’t give you at least 30 minutes notice in advance, we will happily give you a FREE Hour of Service on your plumbing job.
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Does not apply to quoted jobs.
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Deposits
Deposits are not refundable however partial or total refunds of deposits may be made at the sole discretion of Salmon Plumbing.
Cancellations
Salmon Plumbing reserve the right to charge for lost time as a result of cancellations and or postponement made less than 2 business days from the scheduled appointment time.
Warranties
Salmon Plumbing offers a 6 and half year warranty as per the Queensland Building & Construction Commission (QBCC).
In Brisbane, roof water systems are often treated as a simple part of the build process. In reality, they are one of the most important systems on a property. During high-intensity storm events, a roof drainage system becomes the first line of defence against water ingress, structural damage, erosion, and long-term moisture problems.
An effective roof water system relies on gutter capacity, downpipes, overflow management, roof pitch, and ground drainage working together. If one component is undersized or incorrectly installed, water can back up, overflow, track internally, and eventually find the weakest point in the structure.
As veteran plumbing expert John Salmon explains:
“Roof drainage only works properly when every part of the system is designed together. If one component is undersized or installed incorrectly, the entire system becomes vulnerable.”
Sizing gutters and downpipes for effective drainage
Proper roof drainage design begins with compliance with AS 3500, Australia’s plumbing and drainage code. This standard governs how roof water systems should be designed based on roof size, rainfall intensity, roof pitch, gutter fall, and downpipe capacity.
One of the most misunderstood aspects of roof drainage design is the concept of the ‘one-in-20 storm event’. This does not mean a storm that occurs once every 20 years. It refers to rainfall intensity and the statistical severity of a storm event, particularly how much rain can fall within a short period, often measured over five minutes. It describes the level of rainfall intensity a system should be designed to handle during severe storm conditions.
Why gutter size and installation matters
One of the most common problems affecting roof drainage performance is undersized guttering. Many homes that should be fitted with 175mm gutters are instead installed with 150mm systems. This choice is often driven by cost or appearance. While smaller gutters may be less visually intrusive, they significantly reduce drainage capacity, particularly on larger roof spans during heavy rainfall.
Gutter performance also depends on the correct fall and installation, particularly between the front and rear gutter edges. Unfortunately, incorrect installation is common; gutters are installed level or with the rear edge lower than the front. Under heavy rainfall, this incorrect fall causes water to track internally instead of safely away.
This issue becomes even more critical with box gutter systems. Unlike traditional eave gutters, box gutters can discharge directly into a property during heavy rainfall, making correct design and overflow management critical.
The importance of correct downpipe sizing
Gutters collect water, but downpipes determine how quickly that water can leave the roof system. If downpipes are undersized or insufficient in number, water accumulates within the guttering system faster than it can flow away. Simply increasing gutter size without increasing downpipe capacity often achieves very little. This is why AS 3500 sizing calculations are essential. They ensure roof drainage systems are designed to manage realistic stormwater loads rather than relying on visual assumptions or minimum construction standards.
Managing stormwater after it leaves the roof
An effective roof water system does not end once water reaches the downpipe.
Ground-level drainage is equally important because stormwater still needs to be dispersed safely away from a home or building. If this stage of the system is overlooked, water can accumulate around the property and create entirely different structural problems.
French drains are often one of the most effective long-term solutions because they manage both surface water and subsurface groundwater movement simultaneously and require no maintenance.
Why integrated roof water system design matters
An effective roof water system relies on the overall catchment design, gutter capacity, downpipe sizing, overflow management and stormwater dispersion. If one part underperforms, the entire system becomes compromised.
Book a professional roof water system assessment today with the expert team at Salmon Plumbing to ensure your property is prepared for Brisbane’s severe rainfall conditions and future storm events.
