In our regular monthly column – ‘An Inspector calls’ – Total Contractor has teamed up with the pitched and flat roofing experts at BMI UK & Ireland to help you avoid the common pitfalls that can often cost you both time and money, and ultimately help you achieve roofing success.
This month the Inspector looks at the consequences of allowing underlay to drape into gutters.
Most will now know that draping underlay into a gutter allows liquid to be drawn back into the roof
There was a time when this particular error was seen everywhere on the eaves of pitched roofs. To ensure the flow of rainwater from the underlay to the gutter, it would be left to overhang the roof and draped into the gutter itself.
It seemed like a good idea at the time, yet it was a costly mistake. Most will now know that draping underlay into a gutter allows liquid to be drawn back into the roof. It will degrade the bottom edges of the membrane itself, eventually start to rot the fascia boards and ultimately will create an area of negative fall and ponding beneath the first few courses of tiles.
Hard work from a simple oversight
Contractors have spent years repairing and replacing underlay, facias and even supporting timbers thanks to the damage caused by this simple oversight. It’s taken some time, yet on the whole the sector has come to learn this lesson and underlay support trays are now commonplace in the market. A simple, low-cost solution to this problem, the tray creates a solid base for the bottom edge of the underlay to sit upon and replaces the old underlay drape as a method of allowing rainwater to drain off from the roof into the gutter.
Because it does involve some extra work and some (marginal) extra cost, there will still be a few installers who choose to work in the old-fashioned way and one still has to inspect roofs where the drape is in place.
So, it’s advisable not to take this shortcut. It is not only very damaging to the long-term performance of the roof, it is also highly noticeable and is almost certain to be picked up during any kind of sign off or inspection, not to mention spoiling the overall look of the job.
Avoid unnecessary headaches
In this day and age, where all roofs are fully fixed and all perimeters such as the eaves are twice fixed, this is no longer a simple solution to rectifying this problem. Having to disturb an entire double fixed row of tiles could result in having to not only supply new trays and tiles, but also facias as a result of damage caused by existing penetrations. Our advice would be to use underlay support trays to avoid this unnecessary headache.