roof sheeting
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Roof Sheeting – What Your Building Inspector will Check

Roof Sheeting—Is Yours Up To Scratch?

There’s nothing quite like the sound of rain drumming on a roof, especially when you’re snug and dry inside. Roof sheeting is a durable, lightweight and cost-effective alternative to roof tiles. It also forms part of the characteristic appeal of our much-loved Queenslanders. Unfortunately, it’s not without its own unique set of problems. If you’re looking to purchase a property with a sheet roof, a roof inspection by a qualified and experienced building and roof inspector is critical. It can mean the difference between snapping up your dream home and avoiding a leaking, costly nightmare. If roofing problems are not detected, your home could be suddenly inundated with water during the next Brisbane downpour. Worse still, your roof or ceiling could collapse with catastrophic consequences for you and your family.

Types of roof sheeting in Australia

There are several types of roof sheeting available in Australia. The problems you might encounter with your roof depend on what type of sheet roof you have: metal cladding, fibre-cement sheeting or polycarbonate, plastic or fibreglass. Here, we’ll focus mainly on sheet metal roofs.

Metal roof sheeting

Metal roof sheeting is by far one of the most popular forms of roof cladding. Historically, Brisbane’s unique climate, its heat, humidity and high rainfall, meant that traditional roofing materials were not as practical, readily available or affordable (due to the high costs of transportation). A more practical, alternative roofing material was sought.

Queensland’s rich reserves of iron ore provided the ideal solution: corrugated iron roofing and, later, corrugated galvanised steel roofing. It was light in weight when compared to the alternatives, but also strong and durable. The peaks (ridges) and troughs (valleys) were the secret to providing rigidity and strength. It was also able to be manufactured in large quantities and was stackable, allowing for easier transportation over long distances. Its versatility also meant it could also be used as wall cladding.

Take a look around most Brisbane suburbs and you’ll spot an old Queenslander-style home featuring a steeply pitched corrugated iron or galvanised steel roof. So successful was sheet metal roofing that many contemporary homes feature sheet metal roofs. Nowadays, roof sheeting can be manufactured in an endless array of colours and from a wide range of metals including steel, zinc and aluminium.

How problems with sheet roofs arise

When a sheet metal roof fails, it could be something as small as a leak or as large and as shocking as a roof collapse. Roof failure can normally be traced back to one of more of the following problems:

• the type of roof sheeting used and whether it is suitable for the purpose intended or compatible with other materials used

• mistakes made in the way the roof was designed or installed, such as inadequate drainage or ventilation, inadequate roof flashing or shoddy workmanship

• post-installation changes, such as movement in the roof or the underlying structure, extreme weather conditions and the effects of weathering over time.

All roofs have a natural lifespan, but this can be dramatically shortened under certain circumstances.

Incompatible materials used in sheet metal roofs

If incompatible materials are used in the installation of a roof, the result can be disastrous. This is due to a phenomenon known as galvanic or bi-metallic corrosion. It’s an electrochemical process that can have the effect of dramatically accelerating corrosion, or rusting, in a roof. This will greatly reduce the durability and longevity of a roof.

Copper and lead are metals that can trigger galvanic corrosion if in contact with other metals such as zinc. In relation to roofing, this means that the use of copper piping or lead flashing can be a huge problem if in contact with certain types of sheeting, such as ZINCALUME® or COLOURBOND® sheet metal roofing. For that reason it’s recommended the use of incompatible metals be avoided wherever possible. If contact between incompatible metals is unavoidable, then steps must be taken to adequately insulate or shield one from another.

A roof can develop very significant problems if galvanic corrosion results from a poor choice in roofing materials. An experienced roof inspector will inspect a roof to ascertain whether incompatible roofing materials have been used and whether there is any evidence of galvanic corrosion.

Roof pitch or roof slope problems in sheet roofs

The pitch, or slope, of a roof can also lead to problems in a sheeting roof. The pitch assists rainwater to drain away so that it won’t pool and cause damage over time. A steep roof also assists hot air to rise away from living areas into the roof space, cooling the home.

When a roof is designed, the angles at which the roof sheeting will sit need to be accurately calculated. The angles are important because they limit the variety of roofing materials that can be used. For example, corrugated sheet metal roofing is suitable for quite steeply pitched roofs but is unsuitable for flatter roofs. Most roof sheeting manufacturers specify a minimum pitch or angle that their product can be installed at. This is to ensure that leaks do not develop.

Because sheet metal roofing is a lightweight and sometimes cheaper option than a concrete tiled roof, it’s often used when an alternative roofing material should have been used. A roof inspector can tell you if the type of roof cladding you have is suitable for the pitch of your roof.

Inadequate drainage (roof plumbing) and ventilation in a sheet roof

The Australian Government’s Bureau of Meteorology records the historical average annual rainfall for Brisbane as being 1048.5 mm. For this reason, the design and construction of a sheet roof must incorporate adequate drainage. It’s also regulated by the National Constructions Code and the Plumbing Code of Australia.

Blocked or inadequate roof plumbing is a serious problem in a sheet roof. It can lead to water pooling, overflowing gutters and water finding an alternative route to the ground … into your roof space and through your ceilings. Your roof should be watertight, but it can’t do its job properly when there is nowhere for water to escape to. Gutters and downpipes that don’t accommodate the volume of water they should will contribute to leaks. In turn, a roof leak will cause mould, odour and structural problems such as wood rot in the trusses and beams of a roof, as well as damage to walls and ceilings. Left undetected for long enough, this can undermine the structural integrity of the roof. In the long-term, it could lead to roof or ceiling collapse, which can be extremely dangerous.

Ventilation is equally important in a sheet roof. The roof space should allow for a free flow of air. Sheet metal roofs heat up quickly and a steeply pitched roof will also lead to a rapid accumulation of heat in the roof space, which will need to escape. The process of the heat escaping at the top draws air in and through the house, which assists in cooling the home by way of hot air flowing upwards. Roof vents do this. If a sheet roof is not adequately ventilated, the hot air will be trapped.

A roof inspector will check whether a roof is adequately ventilated and whether the roof plumbing is suitable, meets Australian Standards (AS/NZS 3500) and has been properly installed.

Weather damage in sheet roofs

Brisbane’s challenging climate, our frequent storms and hail, wind, heat and humidity is testing for the strongest and most resilient of roofing materials. During extreme weather events, high winds can get under the edges of roof sheeting and lift it or even peel it from a roof completely. Contact between the roof and fallen branches can result in punctures or complete penetration of all layers of the roof including the waterproofing, resulting in leaks. Large hailstones can also cause damage. A roof exposed to strong winds needs to be constructed with adequate mountings, such as roof screws. These also cause penetrations in the roof, so roof flashing and other measures need to be installed to ensure that they do not cause leaks.

In terms of hotter weather, sheet metal roofs can become extremely hot very quickly, resulting in rapid expansion and contraction from day to night. This can create significant movement in the roof over time. Not only can this be noisy but it can also shear the roofing from its mountings over time. If a roof has not been built to withstand the inevitable expansion and contraction, significant problems including leaks can develop. A roof needs to be able to move without tearing against roof fixings.

In addition to the problems caused by weather conditions, proximity to the sea can be a recipe for disaster for a sheet metal roof. The higher levels of salt in the air can accelerate the corrosion process. The Building Code of Australia (BCA) is just one of many regulatory documents governing the building of homes in Australia. In relation to roofing, the BCA is quite specific about particular aspects of roof construction and design. For example, homes being built within one kilometre of the sea are subject to stricter regulation because of higher levels of salinity, which lead to accelerated corrosion in metal roofing. Certain types of roof coatings build to withstand the salinity are also recommended. A roof inspector can tell you if a roof complies with these requirements.

Settlement and subsidence and their effect on a sheet roof

A sheet roof can be damaged over time with the movement that accompanies the settlement of a house after its construction. Settlement is a normal process in which a house responds to the compaction of the soil on which it sits over a period of months or even years. Sometimes the movement is so severe or is exacerbated by factors such as drainage issue that it leads to subsidence, which is a severe movement in the house. The roof of the property can become a casualty of this movement and might not continue to provide the level of protection from the elements that it once did. A roof and building inspector can check for subsidence and whether it has affected your roof.

Asbestos in and under sheet roofs

Depending on the age of your property, the roofing materials used may contain asbestos, a leading cause of mesothelioma, asbestosis and lung cancer. Common culprits include roofs made from corrugated or flat fibro-cement sheeting. Whilst asbestos is in a bonded or non-friable form generally in this kind of roof, damage or weathering of the roof can lead to potential exposure to asbestos. Also, older forms of roof insulation may also contain asbestos. A qualified roof inspector will check whether your roof or roof space contains asbestos and give advice about options available to you.

Why you should get a roof inspection

To the untrained eye, a roof might look fine, but an experienced roof inspector will be able to spot any problems immediately. A thorough roof inspection will assist you to make an informed choice about whether to put in an offer on a house, make a lower offer than you otherwise might, or walk away. A roof inspector will also be able to advise you as to:

• whether your roof meets Australian Standards, complies with the National Construction Code (NCC), Building Code of Australia (BCA), Plumbing Code of Australia and local by-laws

• whether installation of roof sheeting has been in accordance with manufacturer specifications

• what problems are already present or are likely to develop over time

• the options available to you to address any problems

• the likely cost of any necessary remedial work.

A good roof inspector won’t just stand on the footpath and look at your roof from a distance. They will get up on it and inside the roof space. They will check the surface of the roof sheeting and will look closely around penetrations such as skylights, chimneys and vents. They will look for the telltale signs of leaks on your ceilings and interior walls. They will use infra-red thermography to detect invisible leaks and other problem areas. They will also look for evidence of pests, such as termites. You can expect them to photograph and document problem areas and give you unbiased, sensible advice.

Getting a comprehensive roof inspection by an experienced and qualified roof and building inspector is a small investment compared to the enormous costs that can follow when your roof fails to do what it is supposed to.

Call Action Property Inspections today on (07) 3201 2666 or freecall 1800 642 465


About Andrew Mackintosh

Andrew Mackintosh has been answering home inspection questions in the greater Brisbane area since 1995. He has personally carried out over 20,000 building inspections and is a licensed builder and licensed building inspector, Member of Queensland Master Builders Association & Institute of Building Consultants. Being the business owner and the inspector, Andrew is passionate about providing clients with excellent customer service, value for money, honest, unbiased, thorough inspection and reporting in a professional and timely manner to allow clients to make informed decisions when purchasing property.

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