A correctly installed flashing should not have any issues throughout its lifespan, unfortunately if not installed correctly then the lead flashing can run into some issues. Lead should only be installed by experienced lead specialists as they are trained and experienced in all of the lead regulations and specifications to ensure a long-lasting product. Whilst some flashings can be relatively simple to install therefore many builders or roofers will take the work on, they generally are not knowledgeable in leadwork therefore unknowingly install it incorrectly.

Some common mistakes are:

• Over/under fixing
• Incorrect code or thickness used
• Incorrect jointing method
• Over sizing of lead flashing
• Minimum specifications not met
• Thermal movement not allowed for
• Incorrect fixings

Whilst these may seem simple mistakes to make, if just one of these mistakes are made the lead flashings life-span will be severely reduced. It is very important to ensure a competent lead tradesman is used when installing lead flashings.

How long do lead flashings last?

Lead sheet has been to last over 200 years which as a result makes it one of the best materials to use in the construction industry especially in the Sydney roofing industry. Lead flashings are extremely corrosion and weather resistant which is one of the main reasons they are the premium choice when flashing a roof in Sydney. Lead flashings are used on most heritage building due to the longevity of lead. If installed correctly lead flashing will last centuries however if the design and installation of the lead flashing is incorrect, the lead can fail within a matter of months.

Why Do Lead flashing last so long?

We know that lead flashings can resist the external elements better than any other roofing materials but how does lead do it? The basic theory is that when rainwater falls it contains a certain amount of dissolved carbon dioxide which attacks the lead causing a lead carbonate to form. This layer sticks to the surface of the lead and gradually thickens to create a protective layer/patina which prevents the lead from any further attacks.

What causes lead flashings to fail?

There are 4 main reasons that would cause the lead flashings to fail, these are:

• Oversized sheet lengths
• Incorrect jointing method
• Insufficient lap
• Over or under fixing

Oversized Sheet Lengths

Due to thermal expansion and contraction of lead the size of the lengths that lead flashings are installed in are very important. Whilst every situation is different there are some general rules of thumb in which would be suitable for most scenarios. Lead flashings should be installed in 1.5m lengths, this generally works out to be very economical at the lead rolls come in 3m lengths. This size has been proven over decades to ensure the lead will last and continue to function properly. If lead is installed over this size the chances of the lead flashing failing increases significantly. This is due to the lead expanding and contracting, when the lengths are too long the lead cannot move as freely as it could when installed in smaller lengths therefore the lead starts to bulge in certain areas of the flashing. When this continues to happen over time, these bulges will eventually turn into splits which will allow water to penetrate through the lead flashing.

Incorrect Jointing Methods

When a lead flashing is installed into a wall of a Sydney commercial or residential buidling, a 25mm deep chase is normally cut into the wall, if a brick wall it would be dressed into a joint rather than cutting into the brickwork. This joint is very susceptible to failing if not addressed correctly. Due to the expansion and contraction of lead, whatever material is used to fill and seal this joint needs to be able to flex to allow for the thermal movement. It is very common to point the joint back up with mortar, and whilst this is an acceptable method, our experience shows that over time the mortar will crack due to the movement of the lead and the joint will eventually fail. It is possible also to add some lime to the mix will supposedly allows for more movement, however it is still not our preferred method. If installed correctly, a polyurethane sealant is the preferred choice to seal the lead to the wall. This is because it creates a completely waterproof seal and allows for the thermal movement of the lead, and as a bonus it can come in a range of colours to suit either the lead colour or the joint colour.

Insufficient Lap

Whilst lapping the lead correctly is extremely simple, if the lead flashing is incorrectly lapped this will allow the most water to penetrate the building. Depending on the flashing and the situation the size of the lap will vary, however always allow more than less. On vertical flashings for buildings in Sydney 150mm side lap is recommended and a minimum of 75mm on a vertical lap. When lapping on a roof or slope the 75mm vertical rule applies, simply place a level on the roof level and where 75mm hits the roof vertically this point to the point where the level is touching the roof is the size of the lap. The reason why the correct lap is so important is if the lap is too small the water can track between the lead sheets and enter the building.

Over or Under Fixing

As with all lead work and lead flashings the fixing method is very important. Lead flashings need to be able to move to allow for thermal expansion, if the lead has too many fixings, then it will restrict the lead from moving. This will lead the lead to crack and fail over time. However, if the lead is under fixed the lead flashing may move out of position allow water to penetrate the building. This could also lead to the lead falling off the roof potentially causing harm to a person or damage to another building.

The best way to guarantee that your lead flashings will last a very long time is to get them professional installed by trained experts. At Bespoke Leadwork we specialise in all lead work so you can be sure that you will be getting professionals who can guarantee that your flashings will not only look good but will last.