Updated July 2024 by Andrew Mackintosh
Roof flashing is the most effective way to prevent water leaks into your property. It is essential as it keeps your home weather-resistant and waterproof. When rain or hail falls on the roof, any joints, angles or penetrations need to be protected from water. Some parts of a roof are more prone to water leaks – for example inverted angles and penetrations. Roof flashing provides the protection needed to redirect water away from the crevice. In some cases, it can be difficult to identify whether the flashing in place is adequate or still functional on the roof. An inspection of the roof cavity and internal ceiling can give an indication of the adequacy of the flashings.
Thoroughly inspecting roof flashing is a challenge and one that inexperienced building inspectors may struggle with. Queensland law around flashing requirements has changed over the years so the flashing you’re inspecting may not meet code, or, may be excluded from the code, depending on the era of the house. Even after more than three decades in this industry, I still find roof flashing one of the most challenging elements of the pre-purchase property inspection.
To understand how flashing works and why it’s important to have it installed, read on for our explanations and tips.
What is roof flashing?
Roof flashing is a material used to mould around penetrations or laid along a join in components to direct water away. This protects the building from internal water damage.
When you look from the ground view at a roof, it can be difficult to locate where the flashings are. But with a quick walk around your property, you may see penetrations like the toilet vent or a chimney. Sometimes you will see a metal, lead or rubber moulding around this penetration. This is called a flashing and plays an important part in protecting your roof cavity from water leaks and damage.
The flashing can come in a variety of materials. It’s usually thin to allow for ease of moulding around the roof feature while adhering to the roof surface.
The most common materials used for flashing in Australia on tiled and metal roofs are lead, rubber, copper and galvanised sheet metal.
What is counter flashing?
Counter flashing is another term for cover flashing or cap flashing. It’s used around the chimney to protect your roof and any water seeping through the chimney base.
Materials
Lead sheeting used to be one of the most common materials used in the manufacture of roof flashing and is still used today. Lead is malleable and easy to cut and shape and very effective. To some degree lead is falling out of favour for use in flashing, especially with the increased popularity of directing run-off to rain water tanks as lead contamination in tank water can have serious implications. There is also the availability of cheaper and more lightweight products that are also effective. Powdercoated steel flashing and aluminium flashing are much more commonplace now. Roof flashing materials can also be made from a bitumen, zinc or even copper.
Different roof flashing materials suit different types of roofs. Corrugated roof flashing can differ greatly from flat roof flashing, tile roof flashing or slate roof flashing.
What can go wrong with roof flashing?
Roof flashing problems can arise for a number of reasons.
The roof flashing may have been poorly installed in the first place, providing an inadequate, incomplete barrier to water. It may have been poorly shaped for its location or joints in the flashing may be open and not sealed or the flashing may be fretting and cracking with age.
Alternatively, an accumulation of debris; leaves, dirt etc can build up over time and have the effect of diverting water that the flashing is supposed to direct away, resulting in the water pooling and finding an alternative way in. A build-up of moss or other vegetation can also lead to compromised roof flashing. The roof flashing may have even been damaged by rodents or pests such as Indian mynah birds or possums aggressively trying to find a way into the roof space for shelter or nesting purposes.
Damage to the roof flashing can also occur when there is an acute event such as branches or even a tree falling onto the roof. Flashing can also come loose in high winds or be accidentally punctured or damaged when other works are being carried out on the property. Your flashing can be rendered ineffective through the movement of the structure underneath it or by the constant cycle of expansion and contraction in roofing tiles or other materials caused by extremes in temperature.
Finally, problems can also arise when the roof flashing deteriorates over time due to exposure to the elements (eg. rust or oxidisation) and is no longer impervious to water.
Is it a big concern?
The main purpose of roof flashing is to keep the house underneath dry. Failed roof flashing simply can’t do this. Water penetration can be a very serious problem in a home. Water will always flow downwards to the lowest point possible, meaning that the damage caused by a leak may not always show up directly where the damaged flashing is located. It will usually show up as stained ceiling linings or internal roof decay, however, could even be underfoot, rotting your floorboards.
Over time, leaks caused by inadequate or damaged roof flashing can lead to damage to the ceiling linings and even a ceiling collapse.
Water leakage caused by failed roof flashing can cause damp, mould and mildew in a property. Moisture can damage paintwork and rot timber. Mould can also exacerbate respiratory problems such as asthma, especially in immuno-compromised children or the elderly.
Repairing and replacing roof flashing
Some problems can be easily addressed with simple repairs. The materials are readily available at your local hardware store. However, the requisite experience isn’t. For roof flashing to be repaired properly, it’s probably best to call in a roofing expert familiar with, and well equipped for, working at height. To adequately repair or replace faulty, damaged or inadequate flashing they’ll also need to have a fairly extensive understanding of fluid dynamics and how the water will drain away. Simply painting over the mould or mildew just hides the problem and doesn’t address the underlying cause at all, allowing it to progressively worsen.
Unfortunately, many roof problems go completely unnoticed until they cause serious damage, sometimes even structural damage to your home. By that stage, repairs can be incredibly expensive and time-consuming.
What are the consequences of damaged flashing and not getting it repaired?
Damaged flashing will potentially allow water through the unprotected crevice, causing internal damage to the home. This could result in a wet patch on a ceiling which will then need to be repaired or replaced.
Water leaks in a roof can create problems within the property, the worst being a ceiling collapse or wet rot in the timber joists and framing which can affect the structural integrity of the home.
Collapsed or sagging ceilings can be visually displeasing and problematic to repair as they will require new plaster sheeting and painting.
Organising a building inspection of a property you intend to purchase is wise and can give you peace of mind.
Damaged flashing may not be a deal breaker as it can be repaired or replaced. But this can totally depend on how long the leak has been occurring and what the undetected water leaks have initiated in the structure of the property.
It can be hard to identify damaged flashing and other defects during an open house inspection. That is why you should always get a qualified building inspector in to do a pre-purchase inspection, before the contract goes unconditional.