Many who have worked in the industry for decades or more could be guilty of taking a "she'll be right" approach to metal roofing installations.

Most of the time you'll walk away without a problem, but it's not until your work is truly put to the test that you realise how compliant that metal roofing installation was.

As we've witnessed in recent years, this is usually after Mother Nature has turned up the dial to extreme.

Mark Alexander is no stranger to metal roofing installations and their failures. For many years he has worked on projects of varying sizes, types and locations as part of his business, Alexander and Associates – from dairies in South Australia to residential towers in Bangkok; just about every type of commercial and industrial building out there.

This led him to be at the forefront of industry technology and regulatory developments and he has also represented the industry at many state and national forums, including as president of both the Victorian and National Chapters of the Association of Hydraulic Services Consultants (AHSCA).

While Alexander and Associates began as a hydraulic engineering company in 1994, an increase in requests for expert witness reports in plumbing failures and litigation matters saw Mark decide to focus solely on this side of the business in 2008.

"People design and install a metal roof and everyone thinks they've done a good job. Then we get a big rainstorm and there's significant property damage – it might be that the roof wasn't the primary cause of the flooding, but it might be the secondary cause," he says.

"By the time I am involved in a project, significant property damage and losses have normally already occurred. In most cases it's very expensive to undertake the modification works to rectify the roof for it to become code compliant.

"Then, quite often, extended litigation is required to recover the losses from the various parties responsible. This can include design engineers, architects, builders and roof plumbers."

In recent times, some major corporations have asked Alexander and Associates to inspect their projects before they take ownership of the roof from the builder.

"I still haven't inspected a roof where significant issues haven't been identified. I go to roofs all the time where the design engineer, builder or roof plumber honestly thinks the installation is compliant, however it becomes clear that their understanding of the requirements is limited."

To add complexity to the situation, a lot of the time it is difficult to pinpoint who is to blame for the problem: was it a non-compliant design, or a non-compliant installation?

Throughout Australia, different trades are responsible for designing and installing metal roofs. In Victoria, regulations dictate that design and installation of roof plumbing is the plumber's responsibility.

"The common denominator I see all over the industry – from engineers, architects, designers, builders and plumbers – is they think installing a metal roof and the associated drainage systems is easy. Just because you install another downpipe or overflow pop, that doesn't necessarily mean the overall system can drain more water," Mark says.

"They don't understand the advanced hydraulics associated with large roof catchments. Considerations related to turbulent flows and backwater curves generated in high velocity gutters are either generally ignored, or alternatively, the designer is completely ignorant to the related flow dynamics."

The Usual Suspects

Mark notes that some of the most common issues that he has come across include:

  • Non-compliant rain heads and sumps.
  • Lack of gradient for internal box gutters.
  • Insufficient provision for thermal expansion and contraction.
  • Inadequate overflow provisions.
  • Failure to allow suitable surcharge where downpipes are connected to drains.
  • Design flow rates exceeding the provisions of AS/NZS 3500.3 Plumbing and Drainage – Stormwater drainage.

"There are some so-called professionals using non-certified online calculations to size gutters, sumps and overflows outside the provisions of AS/NZS 3500.3. Unfortunately these so-called 'calculators' have a number of deficiencies and among other things, do not consider the backwater curves generated by turbulent flows.

"We also get a lot of disputes about the sheets and materials being damaged while under construction. There's a hell of a lot of premature corrosion from cuttings and filings left on the roof or from following trades damaging it."

For Peter Coll, Interline Roofing general manager and director of the Residential Metal Roofing Industry Association of Victoria, the issues are many and varied.

He is somewhat a veteran in the industry, having worked on metal roofing installations alongside his father and brother in the family business, as well as other notable roofing companies over the years. One issue that has been cropping up lately is condensation under roofs.

"Because there is such a temperature difference outside and inside, and we're doing such a good job of locking these houses up tight for a star rating, there's not enough ventilation or equilibrium between the two temperatures," he explains.

"We've tried putting roof ventilators in but the problem with frosty mornings is that they don't work because there is no wind outside. This means you have to start installing mechanical ventilators."

Peter goes on to say that the issues surrounding the design and installation of a metal roof are only part of the problem. The other extends to the wider difficulties being faced by the building industry, which has seen countless metal roofing companies close their doors.

Based in Victoria, Interline Roofing works mostly in the residential space and currently has a full sheet metal shop to produce their fascia and rainwater goods.

Even though things are tough at the moment, Peter is confident that their ability to produce a quality product will keep them ahead of the game.

"The market across the board is the worst it's been in our 30 years of operation. Becoming a profitable player in this marketplace is becoming harder," he says.

"We're trying to stick to our guns and offer our customers a good product at a level that will see us be here next year. If we can't compete on mass price, we need to offer the smartest possible option.

"It's the way the market is heading – you need to offer something that's a point of difference to demonstrate your expertise."

Like many other aspects of the building industry, this all comes back to playing by the rules.

A question of compliance

Metal roofing installations must comply with the relevant Australian Standard and any additional state-based regulations. The question though, is how rigorously is that work tested and checked?

Mark argues that a lot of faults slip through the approval system simply because those inspecting the building may not have a good awareness of sizing, overflow or gradients. Unfortunately, these faults only come to the surface following a major weather event where there is significant property damage.

"In major events that sometimes occur years after the roof has been completed and hundreds of buildings could be affected. You scratch your head and wonder why all of these failures are happening," Mark says.

"The silly thing is that Australia's regulations are probably the best in the world. In just about every single case, the principal cause of failure has been because the metal roof hasn't complied with the regulations."

He notes that AS/NZS 3500.3 was published in 1990 in response to the concerning amount of buildings getting flooded during moderate rainfall events. A lot of research was done in the nine years preceding the change and resulted in the introduction of a mandatory 100% overflow capacity. But even after more than 20 years, a lot of builders, roof plumbers, architects and engineers haven't changed their ways.

"Some designers are also using vastly outdated technical references such as superseded CSIRO papers and superseded Experimental Building Station references. These references were published prior to the research undertaken as part of the development for AS/NZS 3500.3 and therefore do not incorporate the important aspects identified in the hydraulic flow modelling undertaken at the University of Technology Sydney. The superseded references also do not have suitable provision for gutter sizing and overflow provisions required to provide 100% overflow protection in the most commonly used roof drainage configurations," he says.

"For some reason, I am finding that some professionals are using these deficient methods of design instead of using the requirements of AS/NZS 3500.3 as regulated by the Building Code of Australia."
Interestingly, Mark explains that he has never been involved in a job that has fully complied with AS/NZS 3500.3 and failed, unless that failure was directly attributed to a blockage of some kind. This just goes to show how important it is for the trades involved to take compliance seriously.

"For every major failure I investigate, there's a plumber, builder, engineer or architect at the end of the line saying they've installed or designed roof drainage systems for 20 years in a particular, non-compliant manner and never had a problem. We need to change that attitude in the industry; it will save everyone a lot of time and money."

In their defence, though, Mark also notes that the National Construction Code and associated regulations can be hard to understand – which ultimately plays a role in non-compliance.

"I speak to a lot of people – skilled architects, skilled engineers and skilled plumbers – and they have difficulty grasping the advanced hydraulics. The message is being lost somewhere – it becomes too difficult for them to digest quickly and therefore alternate, less effective and incorrect assumptions are being made."

As a member of the WS-014-03 Standards Committee that manages AS/NZS 3500.3, Mark believes further advances can be made and encourages comments and suggestions from the entire industry. 

"One of the committee's objectives is to simplify some of the concepts and directives presented. Sometimes this might involve further notations and directives, or alternatively it may mandate that additional information is provided."

A solid education

As mentioned earlier, one of the most difficult things in metal roofing installations is the fact that it's handled by different professions in different states. Given the complexity of the system, the onus is on education.

"When we talk about spouting, overflows, sizing, gradients and how they're all linked together, it really needs some training – particularly when we get into large and advanced projects," Mark says.

"Roof plumbers may have the necessary knowledge, but that doesn't mean a builder in another state does, or even an architect or engineer does."

Peter hopes the Residential Metal Roofing Industry Association of Victoria will provide a gateway for the industry to be as proactive as possible and bring all the players together to solve some common issues – not just so everyone is on the same page regarding the technicalities of an installation, but also in terms of the training available to apprentices.

"We're looking to develop a training program for roof plumbers, as a lot of apprentices fall off because they learn stuff at work but don't get to apply what they learn at trade school," he says.

"We're working closely with Holmesglen TAFE in Melbourne to re-engineer the apprenticeship so it is more upfront with the roofing aspects – this might help to keep them engaged with the course and invested enough to finish it off and get qualified."

While the association is currently only restricted to Victoria, Peter notes that there are plans for it to become a national body. This move is all the more important, particularly given the impending introduction of a national licensing scheme.

"At the moment they're looking to deregister roofing as part of national licensing, which would be catastrophic for us and the entire industry. By taking the licensing away from roofing, cowboys will come in and the quality will drop off even further," he says.

"We're trying to get a national conference together to start a conversation and push the view to keep roofing as a national licence. Sure, it does cost more money upfront but shouldn't we want the best possible standard across the country?"

This is just a selection of the many issues that installers must face when working in the metal roofing sector.

Despite the fact that a roof is a deceitfully complex part of the building makeup, it's essential that all industry players work together to ensure any metal roof performs its role to the best possible standard.

Common roofing faults (Victoria)


AS/NZS Standards


Inadequate roof flashings/cappings which do not provide a weathertight and secure installation.

HB39-1997 CI 8.2


Eaves gutter not installed with the minimum required gradient.

HB114-1998 CI 2.6


Eaves gutter joints not watertight.

HB39-1997 CI 5.8


Roof covering not securely fixed to the structure at the appropriate spacing.

HB39-1997 CI 7.5


Insufficient gutter overflow outlets for dispersing the stormwater where the roof drainage is restricted.

AS/NZS 3500.3:2003 CI 3.7.2
AS/NZS 3500.3:2003 CI 3.7.5


Roof drainage system not installed in a good and workmanlike manner, does not comply with the manufacturer’s installation instructions and to a minimum industry standard.

Plumbing Regulations 2008
Part 3 r.14


Roof coverings and associated flashings not installed in a good and workmanlike manner.

Plumbing Regulations 2008
Part 2 r.14


Inappropriate box gutter size for the roof catchment area.

SAA/SNZ HB114-1998 CI 3.6


Insufficient number of downpipes appropriate for the roof catchment area.

SAA/SNZ HB114-1998 CI 3.4


Inappropriate overflow provision to the sump/rainhead.

AS/NZS 3500.3:2003 CI


This table lists the top 10 fault line items from a pool of just under 425 faults from the audit process for the year 2012/13.
Source: Victorian Building Authority.

Story provided by:    Building & Plumbing Connection -