It is common on extended homes in Lawrence Weston for the addition to have been built at a shallower pitch than the original roof, often because of height restrictions against a boundary or simply to keep the extension lower than the main house. Where two different pitches meet, whether at a valley, a lean-to abutment or a change in roofline, the weatherproofing detail has to work harder than it does on a single, uniform slope, and it is one of the first places a roof will show weakness.
A shallow-pitch section sheds water more slowly than a steeper one, which means standing water and wind-driven rain have more opportunity to find a way under tiles or slates that were only ever designed for a steeper angle. This is why the minimum pitch rating of a roofing material matters so much when an extension is being tiled to look similar to the main house rather than being finished in a material actually suited to a lower pitch, such as a low-pitch interlocking tile or a suitable membrane system.
At the point where pitches meet, valley trays, soakers or secret gutters are typically used to carry water safely away rather than relying on the tiles alone to overlap correctly across an awkward angle. These components need to be formed from a durable material, laid with the correct falls, and dressed under the surrounding covering so that they are not visible but are doing all the real weatherproofing work behind the scenes, channelling water down to the eaves and away from the property rather than letting it pool at the change of angle.
On many of the semis and low-rise blocks in Lawrence Weston, extensions have been added at various points over the decades, sometimes by different builders using different standards, so it is not unusual to find valley and pitch junctions that were never detailed correctly in the first place, with undersized valley linings or tiles used well below their rated pitch. A re-roof is often the first real opportunity to put this right, rather than continuing to patch around a detail that was flawed from the outset.
It is worth noting that pitch changes are not only about tile selection. The underlay used across a pitch change also needs to be continuous and correctly lapped, since a break or gap in the membrane at exactly the point where water is moving fastest across the junction can undo the benefit of correctly chosen tiles above it.
Brunel Roofing Bristol pays close attention to these pitch changes when quoting for a new roof, because getting them right is usually what determines whether a property stays dry through the wetter months of the year. If your home has a mix of roof pitches and you are considering a new roof, get in touch for an inspection and a quote.
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