Do I Need Larger Gutters for My Central Coast Home? A Gutter Sizing Guide from AWS Roofing

You probably need larger gutters if yours spill over the front in heavy rain, if a big section of roof drains into one downpipe, or if you are putting a new metal roof on and the old gutters are already tired. Australia’s National Construction Code sets out how eaves gutters on a house are sized for the local rainfall and the area of roof each downpipe drains.

This guide from AWS Roofing explains how gutter size is worked out for a Central Coast home, what larger gutters and extra downpipes change, and how to tell when your gutters need replacing rather than another patch.

Key takeaways

• Eaves gutters must suit the 5 minute rainfall intensity for the area, set at a 5% annual exceedance probability in the ABCB Housing Provisions, Part 7.4.
• Part 7.4 does not list a Central Coast town. The closest listed localities are Newcastle at 225 mm/h and Avalon, Sydney, at 210 mm/h.
• Each downpipe can serve no more than 12 m of gutter.
• Rusted, sagging or overflowing gutters are a sign it is time for new guttering.

What Are the Advantages of Larger Gutters and Downpipes?

Larger gutters and extra downpipes let your roof drainage carry more water before it spills. The Housing Provisions size a gutter by two things: the design rainfall intensity and the area of roof that drains into each downpipe.

• More water carried away: a larger profile holds more water, so less of it spills over the front of the gutter.
• Less roof per downpipe: adding downpipes means each one drains a smaller area of roof.
• Water kept away from the house: when gutters are sized properly and have overflow measures, the water is directed away from the walls and fascia instead of running down them.

How Do You Decide If You Need Larger Gutters?

Start with what your gutters do in heavy rain. If water pours over the front edge, runs down the walls or pools along the house, the gutters or downpipes are not keeping up. Then look at the roof itself. A long roofline or a large section of roof draining into one downpipe puts more water into that gutter than a small, well-served section does.

If you are planning a new roof, it is a good time to look at the gutters as well. You can read more about this in our guide to larger gutters and gutter replacement for heavy rain.

How Is Gutter Size Worked Out for a Central Coast Home?

Gutter size for a house is worked out from the local 5 minute rainfall intensity and the roof catchment area per downpipe. Under the ABCB Housing Provisions, Part 7.4 Gutters and downpipes (NCC 2022), eaves gutters must handle rain falling at the intensity listed in Table 7.4.3d for a 5% annual exceedance probability. Overflow measures are designed for a 1% annual exceedance probability. NCC 2022 is the edition in force in NSW until NCC 2025 takes effect in NSW on 1 May 2027, and the Part 7.4 values in this guide are the same in both editions.

Table 7.4.3d does not list a Central Coast town. The closest localities it does list are Newcastle to the north, at 225 mm/h for a 5% annual exceedance probability and 316 mm/h for 1%, and Avalon, Sydney, to the south, at 210 mm/h and 287 mm/h. Table 7.4.3a then matches the gutter size to that rainfall intensity and to the area of roof draining into each downpipe.

The same part of the Housing Provisions also sets how eaves gutters are installed:

• Fall: not less than 1:500.
• Brackets: fixed at stop ends and corners, and at not more than 1.2 m centres.
• Overflow: overflow measures that send water away from the building so it does not pond against it, enter it or damage it, even if the stormwater drainage is blocked.

Box gutters are treated separately. The Housing Provisions note that AS/NZS 3500.3 may be used to work out their minimum sizes, falls and overflow, and you can read more in our guide to types of guttering, fascia gutters and box gutters.

Roof Size, Downpipes and Larger Gutters

Roof size matters because gutters are sized by the area of roof each downpipe drains. The Housing Provisions say a downpipe must not serve more than 12 m of gutter length and should sit as close as possible to valley gutters. They also note that insufficient and poorly located downpipes are a frequent cause of poor roof drainage.

On a long roofline or a home with several roof levels, adding additional downpipes or increasing their size gives the water somewhere to go, so the extra volume reaches the stormwater system instead of backing up in the gutter.

Leaf Litter, Gutter Guards and Blocked Gutters

Leaf litter matters because even a correctly sized gutter only works when it is clear. The Housing Provisions say eaves gutters are designed to remove water from a 5% annual exceedance probability rainfall event provided they are not blocked. If your home sits under gum trees or other large trees, check the gutters after heavy leaf fall.

Leaf litter and standing water left in a gutter also speed up rust. If your home gets a lot of leaf fall, larger gutters together with gutter guards will help the water keep moving. Gutter guards can be fitted when we install new guttering on your home. Our guide on how blocked gutters can damage your home explains what happens when the water cannot get away.

When Do Gutters Need Replacing Rather Than Another Patch?

Gutters all rusted and beyond a patch or repair? We install new guttering. Salt in the coastal air eats at metal, and once guttering starts leaking at the joins or sagging between brackets, patch repairs tend to fail again within a season. That is usually the point where new gutters, sized for your roof, make more sense than another round of repairs.

It is usually time to replace your gutters when you notice:

• Rust or holes: water weeps through even when the gutter looks intact.
• Sagging or gaps: the gutter has pulled away from the fascia and no longer sits at the right fall.
• Overflow in heavy rain: water spills behind the gutter and runs down your walls.
• Water damage inside: stained ceilings or fascia rot near the roofline.

A gutter replacement on the Central Coast with AWS Roofing covers removal and disposal of the old guttering, new Colorbond guttering installed to the correct fall, fresh brackets and fixings rather than reused ones, and a check of your downpipes and fascia so the water has somewhere to go. If you are replacing the gutters anyway, that is the time to move to a larger profile.

Are Bigger Gutters Better?

Bigger gutters are better when your current gutters cannot carry the water your roof sheds in heavy rain. The gutter still needs the right fall, enough downpipes in the right places, overflow measures and a clear channel, as set out in Part 7.4 of the Housing Provisions.

Can I Upgrade My Gutters to Handle More Water Flow?

Yes. You can upgrade to a larger gutter profile, add downpipes, or do both. The guttering profiles on our guttering page include the 115 mm Ace Quad and the 150 mm Half Round, which ACE describes as having a greater water capacity than a conventional gutter. We match the profile and colour to your roof and fascia.

Talk to AWS Roofing About New Gutters for Your Home

AWS Roofing is fully licensed and insured, WorkCover accredited and gives written warranties on its work. We inspect your roof to give you an accurate quote, and we’ll explain the gutter size and downpipes we recommend for your home and why. Get in touch for a free, no-obligation quote, or pop into our Charmhaven showroom to see the Colorbond colours in person.