Non-compliant, poorly fitted or retrofitted box gutter rainheads often cause major flooding. Deborah Andrich and Paul Skelton investigate a new solution that meets all the standards.

A group of plumbing industry experts were so tired of seeing box gutter rainheads that didn’t comply with AS/NZS 3500.3 they decided to do something about it.

Too often in the roofing industry, contractors are installing rainheads that just don’t perform. These rainheads then require ‘solutions’ in an attempt to try and achieve some level of performance while attempting to mitigate the blockage and water ingress problems that inevitably occur. This may involve measures such as tin snipping overflow holes, removing components or altering the overall product.

Such measures were considered necessary because you simply could not purchase a compliant box gutter rainhead on the Australian market.  In many cases, the result of these ‘solutions’ is non-compliant as well as ugly, causing overflow flooding in buildings and creating insurance headaches for owners, occupants, builders and plumbers.

The launch of the engineered and compliant Dam Buster box gutter rainhead means that Australian roofing plumbers can at long last install an ‘off the shelf’, easily-fitted rainhead that complies with AS/NZS 3500.3 and also fully meets the ‘deemed to satisfy’ requirements of the National Construction Code (NCC).

The Dam Buster rainhead is designed to perform under the most extreme conditions, including the ‘one in 100 years’ storm mandated under the Standards. In particular it features an inbuilt overflow weir and overflow chute that has been cleverly engineered to allow a free flow of water away from the box gutter and roof installation even with the downpipe fully obstructed.  Johnson Roofing general manager Peter Coll says 95% of rainheads in Australia are non-compliant.

“The reasons can vary from the installed position to the lack of provision for overflow,” Peter says.

“Most rainheads don’t look like the one in the Standard – customers won’t accept it from a cosmetic point of view because you see too much of the box gutter behind it.

“The aesthetics issue has been resolved with the Dam Buster design. I’m kicking myself for not having seen the simplicity of the answer to the problem.”

Currently the Standards require a rainhead to be similar to the one in the specification diagrams of AS/NZS 3500.3:2015, SA HB-114-1998 and SA HB-39-2015.

The description by the Victorian Building Authority states: “The width of the rainhead is to be at least equal to the width of the box gutter and the box gutter needs to be sealed to the rainhead. The hydraulic capacity of the overflow device must be no less than the design flow for the associated box gutter outlet. Overflow devices need to discharge to the atmosphere in such a way as to prevent damage to buildings and property.”

The design developed by the team at Dam Buster features an overflow weir towards the forward face of the rainhead, beyond the downpipe outlet and in alignment with the box gutter outlet.  Across the front is a fascia with a pre-cut secondary egress point (circular or rectangular) for unusually high water flow. Between the weir and the front face of the rainhead is an overflow chute sufficient to provide more than the overflow provision required in AS/NZS 3500.3:2015 (see Figure 1).

This fascia effectively gives a more attractive appearance to the overall rainhead. More important, without a solid base in the main overflow chute the risk of debris such as leaf matter blocking the overflow provision is reduced or eliminated. Even with the overflow provisions achieved and the visual benefits of the fascia, the entire device has been engineered to be more compact than the average rainhead used for an equivalent application (which are more often than not sized with no reference to the Standards on the basis that bigger is better).

With a range of features to assist installation and save costs, including inbuilt attachment points, a box gutter seal and a fully customisable rear converter plate, contractors can quickly and easily fit a Dam Buster to a new build or retrofit one to any existing box gutter application. The design also features pre-set overflow heights and sizes straight from the box, meaning that in most cases the only cutting required is to insert the appropriate downpipe pop in the base. The Dam Buster can also be easily converted onsite for use on eaves guttering using the supplied converter plate, but specific eaves gutter versions are also available off the shelf.

The insurance perspective

Decades of experience tells chartered loss adjuster David Pockett, director of Metropolis Solutions, that overtopping box gutters as a result of blockages in rainheads are responsible for staggering numbers of insurance claims, particularly during storms.

It is quite common for a building to have no actual storm damage such as roofing torn off; in many cases the only damage is caused by box gutters and rainheads failing to cope with the volume of rain, which then floods the property via the ceilings.

“Many people put these events down to that good old ‘one in 100 years’ storm event,” David says.

“But these events have become so common that people are probably only talking about one in 10 years or one in 20 year storms. Buildings should not be flooding in those conditions at all.”

With the sharp rise in contemporary construction has come an equally sharp rise in the use of box gutters and rainheads (see Figure 2).

In years gone by these were rarely found on dwellings – only on commercial buildings. In the ‘old days’ they usually employed a different installation method that mirrored the original Englishdesign, which was also the basis of one of the (compliant) rainhead options set out in AS/NZS 3500.  This system did not cause many problems.

“The Australian Bureau of Statistics tells us that between 18,000 and 20,000 homes are being built in Australia every month, year after year,” David says.

“Even if we assume that only 50% have rainheads for a contemporary design, that equates to almost 10,000 new homes a month, and a typical contemporary style house would have four or five rainheads.

“So we are looking at nearly 50,000 non-compliant rainheads a month going into housing. The problems this will cause should be self-evident to everyone in the industry.”

David says the main problem with modern rainheads is that they choke the box gutter, even if they are well installed and there is no restriction of the box gutter through the parapet.

Modern rainheads are little more than decorative trim boxes designed to cover up the hole in the parapet wall and obscure the end of the box gutter. Small holes and slots hacked in the front face of the rainhead with tin snips or similar tools are woefully inadequate for the potential volume of water involved and which those rain heads are required to safely overflow ‘to atmosphere’ if required.

This is likely to be a significant factor in the epidemic known as ‘leaky building syndrome’, which is rife in multi-unit residential developments.

In David’s experience, water damage from defective roof plumbing in houses and apartments is common. Entire properties can be flooded – ceilings collapse, carpets are saturated, floating timber floors are destroyed and mould takes hold – forcing people out of their homes.

Insurance assessors generally don’t recognise that common rainhead practice is non-compliant and therefore don’t investigate the cause of the damage. This means that claims are paid on face value, especially if there has been a lot of rain.

Many insurers also often use what is called the ‘builders’ model’, in which a panel of builders assesses claims. However, they often lack the experience or the inclination to identify the cause, so again the resultant damages claims are simply paid.

Consumers can potentially be caught in the middle.

“More insurers are using specialist assessors who will recognise non-compliant installations and defects and then deny the claims,” David says.

“The hapless consumer who has recently purchased a dream home or apartment has no idea about rainheads or non-compliance. The property floods and suddenly the specialist assessor representing the insurance company says the roof plumbing installation was not compliant, therefore the claim will be denied.

“As insurers tighten the screws, this is potentially the next ‘flood’ to appear in this area – of denied claims and unhappy home owners. The flow on from that could well be an increase in litigation against plumbers who installed the rainheads not in compliance with the Standards, and also against builders who in many cases have engaged the plumbers.

“A lot of flak continues about non-compliant building cladding, with more being identified every day. Leaky buildings don’t get the same media coverage even though essentially the same issues are involved.

“Once again there has been a lack of enforcement of the Standards by regulators across the country.

“There may be thousands of buildings affected by the cladding problem but there are millions affected by the non-compliance of rainheads. The serious health risks and the damage to property clearly don’t carry much weight in the political scene compared with being burned alive, but both need urgent resolution.

“Leaks have the potential to reduce any domestic home or even a cutting edge contemporary building to Third World standards and also to seriously affect the health of occupants.”

The Dam Buster rainhead patented and engineered design combines years of hydraulic experience and innovative manufacturing techniques to make the seemingly problematic rainhead fully compliant.

Final test certification on the Dam Buster range has now been completed at the ASHCA Research Foundation test rig at The Sunshine Coast University in Queensland and all models have achieved remarkable flow and overflow rates, quite unprecedented in any existing rainhead products and also well in excess of the rates required to pass AS/NZS 3500.3:2015.

Colorbond versions are also available, and powder coating may be specified in any colour the client wants. A curved version is expected to be added in early 2018.