Roofs bear the brunt of adverse weather conditions, whether it be gales, rain, snow, hail or freezing temperatures. For flat roofs in particularly this means a great deal of care and attention is needed to create falls which channel any moisture that ends up on the roof into drains. Whilst these falls were traditionally achieved through structural approaches, tapered insulation systems can now provide a simpler, lighter solution which can also ensure roofs meet the U-values required for a project.
What problems can occur when a flat roof doesn’t drain properly?
Before we look at the different approaches used to create a fall, it’s important to understand why achieving a correct fall is so important.
The most obvious concern for any flat roof is water ponding, where rainwater is allowed to sit on the roof for an extended period of time. This can occur for a number of reasons, including an insufficient or poorly designed fall, blocked drainage channels or roof debris.
As the water sits on the roof, it can cause damage to the waterproofing system, magnifying UV-radiation, weakening bonding adhesives and stripping oils from asphalt. Over time, these can lead materials to become brittle, reducing their lifespan and potentially causing leaks – particularly around junctions in the waterproofing system. This can be exacerbated in the winter months where any standing water can enter tears or gaps in the surface and freeze, opening them up further.
Water which drains slowly, or doesn’t drain at all, can also allow dirt and other sediments to gather on the roof, providing an ideal substrate for vegetation and moss to form. It also adds structural loading to the roof deck. If it is not addressed, this can cause the surface to deflect, allowing even more water to become trapped and potentially lead the surface to fail.