Top 7 problems with the modern roof (and how to fix them)
Balmain builder and designer Mat Wilk reveals the issues with modern roofs, and how the team at Ballast Point Architecture and Construction can help find solutions in the Inner West area. As we covered in a recent blog about modern roofs, many issues we now face stem from the shift from pitched to flat roofs. While flat roofs are stylish and often require less material to build, they are not as effective at shedding water as pitched roofs and often come with engineered solutions that can be susceptible to failure.
1. Lack of overflow
No matter what, there will be a day when downpipes do not cope with a sudden inundation. The downpipe may be blocked by leaves or a tennis ball, or the volume of water exceeds the design specs. In this case, the water will go somewhere and in so many cases, especially with box gutters, the overflow backs up and water flows into the house.
2. Wrong size or poor placement of overflow
We covered lack of overflow in point one, but there is more to it, and it’s important, so I’ll bang on about it just a bit more. Here’s the thing – it’s not just about whether there is an overflow or not, but also how effective it is. Some people think of a roof as a system of troughs and containers: one container – the box gutter – fills up, so drain it into another container, downpipe, or another gutter. In a storm, the system often functions completely differently. Think white water rapids and you get a better idea. The system is messy and dynamic, water gushing and swirling – so the notion of “when this fills up it will tip into there” goes out the window pretty quickly. The overflows need to be adequate in size and appropriately placed to work or they may as well not be there.
3. Inadequate flashing
Flashing is used to connect new and old parts of a roof, and provide a weatherproofing element at the edges and junctions. Inadequate flashing is particularly a problem when a modern extension is added to an existing roof. Sometimes there are three different types of roof coming together at one junction, and the rulebook goes out the window. A creative solution is required. Tile roofers and metal roofers are typically different trades, each builds their own section of the roof, so if the roof leaks who is responsible?
4. Degradation and lack of maintenance
Let’s face it – we focus on things we can see and in the case of most flat roofs nobody (apart from low-flying drones) can see anything up there, particularly on a flat roof. We don’t bother with maintenance until we see damp plasterboard on the inside. With a pitched roof we could see tennis balls, leaves and broken tiles from the ground, so we would feel compelled to clear the gutters and fix the broken tiles.
5. Wind
Even if we build everything to the building code there is still a small chance that if the wind is blowing with the right speed from the right (or wrong!) direction then we will get water ingress, particularly if this condition persists.
6. Reliance on silicone
Silicone breaks down over time, buildings move, silicone is the first layer to fail. If silicone is the only layer between inside and outside, then it’s only a matter of time until the roof leaks without recurring maintenance. Building redundancy into the roof system will ensure when one element fails there is another that takes over, giving you more time to address issues before they become too serious.
7. Not enough fall
If a roof doesn’t have enough fall it won’t work properly and water will back up - it’s that simple. Different roof cladding materials have prescribed minimum falls to allow gravity to do its job, so be sure to check before installing. Be wary of replacing one kind of roof cladding with another - for example, changing a metal roof to a tile roof, or even a clip-lok metal roof to a corrugated metal roof - there may not be enough fall as these materials have different minimum falls to be effective.
OUR SOLUTIONS
1. Create redundancy throughout the system
A sufficient overflow is a good example of a system with built-in redundancy – when the downpipe fails the overflow takes up the slack. We ensure that every part of the roof, and the rest of the house for that matter, is built that way. We tend to not rely on silicone, which inevitably can crack and disintegrate or be ripped apart by movement caused by thermal expansion. But sometimes when the box gutter is too long to transport, we need to build it from parts on site and seal the joints with silicone. In this case we have a back-up plan – we seal the plywood substrate with a waterproofing membrane so that even if the silicone fails the system will still not let water into the house.
2. Rethink gutter and overflow placement
In a proper downpour a box gutter behaves more like a system of white water rapids, but let me ask you this: have you ever seen white water rapids turning 90 degrees? So why do we put box gutters and overflows at 90 degrees to each other? The overflow needs to follow the direction the water is flowing, or it will fail. By default, that puts it at the end of the box gutter.
3. Make gutters self-cleaning
Our box gutters are always open-ended and our sump (water collection point) is created by the rise in the end of the box gutter rather than a square box above the downpipe. What this means is that when the downpipe can’t cope with the amount of water it pushes not only the water but whatever is in the downpipe out the end.
4. Simplify and rationalise roofs where possible
Being a design and build contractor enables us to ensure that the roofs we need to build are designed from the outset to work. This often means that we need to come up with a creative solution where we can redesign a cacophony of roofs into an elegant solution that simplifies the path the water has to take.
5. Go just a bit bigger
Often it doesn’t hurt to upsize from the standard or the engineer’s calculations. For example, upsizing a downpipe from 90mm in diameter to 120mm costs almost nothing and yet nearly doubles its capacity (sounds wrong, but you do the maths). Simply upsizing the diameter of the downpipes will have minimal impact on the rest of the roof system.
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