What Causes a Garage Roof Leak?
When I am called out to inspect a garage roof leak anywhere in Sussex, the first thing I look for is whether we are dealing with actual water ingress or just heavy condensation. Because most garages are uninsulated ‘cold roofs,’ a sudden drop in temperature can cause moisture to condense on the underside of the timber decking. However, if water is actively dripping during rainfall, you have a structural failure in the waterproofing membrane.
Common Failure Points: Thermal Movement and Capillary Action
The most frequent culprits I see are aging pour-and-roll felt roofs that have succumbed to UV degradation and thermal movement. Over the years, the constant expansion and contraction cause the felt to turn brittle, leading to micro-cracking. Once a crack forms, water is drawn in through capillary action, saturating the decking beneath.
Another major point of failure is the perimeter detailing. Poorly installed drip edges or failed lead flashings where the garage meets the main house wall act as funnels for rainwater, especially when driven by heavy coastal winds.
The Right Way to Fix It
A proper repair depends on the extent of the damage to the OSB or plywood decking. If we catch the problem early before rot sets in, a localized repair is entirely possible. For these types of straightforward issues, you can easily book a half-day repair slot with us for an urgent leak assessment and immediate repair. In a half-day, I can cut back the damaged felt, check the structural integrity of the timbers, and patch the area securely using high-performance SBS-modified bitumen to stop the leak dead.
If the leak has been ignored and the timber substrate is soft or suffering from wet rot, simple patch repairs will fail. You cannot bond new felt to saturated timber. In this scenario, we must strip the roof back to the joists and install a completely new garage flat roof system. This involves laying down fresh, treated decking and applying a durable, multi-layer torch-on felt system designed to handle the weather extremes we experience across Sussex.
Calculate Your Costs Instantly
Dealing with a leaking garage shouldn’t involve waiting weeks for a tradesman to guess a price. Now that you understand the technical reasons behind your garage roof leak, you can take the next step without any pressure. Use the free online calculator on my website to get an exact, instant price estimate for the materials and labor required. It takes just 30 seconds, giving you total transparency before I even arrive on site.