When I am called out to inspect a leaking garage roof in Brighton, the root cause is almost always the same: outdated, oxidized bitumen felt that has finally succumbed to thermal movement and coastal weathering. If your garage roof felt is blistering, cracking, or allowing water ingress, patching it is usually a waste of time. The structural decking beneath is likely absorbing moisture, and capillary action will continue to draw water into the timber.
Why Traditional Garage Roof Felt Fails in Sussex
Historically, most flat garage roofs were covered using ‘pour and roll’ oxidized bitumen. While this was the industry standard years ago, it lacks the flexibility required to withstand the temperature fluctuations we experience.
Thermal Shock and UV Degradation
Building materials expand in the heat and contract in the cold. A typical garage roof in Brighton takes a battering from direct UV rays in the summer, causing the decking and felt to expand. In winter, everything contracts. Old oxidized felt becomes brittle over time due to UV degradation. When the roof moves, the rigid felt cannot stretch—so it tears. This usually presents as ‘alligator cracking’ across the surface or splitting at the upstands and drip edges.
Wind Uplift and Coastal Conditions
Brighton and Hove’s coastal climate introduces high wind exposure and salt-laden air. If the edge detailing (the perimeter flashing) fails or was improperly installed without a proper drip batten, high winds create negative pressure that actively lifts the failing felt. Once the wind gets underneath, or salt corrodes the cheap metal edge trims, water bypasses the membrane entirely.
The Modern Solution: SBS-Modified Bitumen
As an independent roofer handling these specific issues across Sussex, I never use outdated materials. The only reliable replacement for a failing garage roof is a high-performance SBS (Styrene Butadiene Styrene) modified bitumen torch-on system.
- Elastomeric Flexibility: The SBS synthetic rubber additive fundamentally changes the bitumen’s physics. It allows the felt to stretch and recover its shape during thermal movement without cracking.
- Robust Three-Layer System: A proper installation isn’t just one sheet of felt. I install a vented base sheet to allow existing trapped moisture to escape, followed by a reinforced underlay, and finally a heavy-duty mineral cap sheet.
- Decking Replacement: I never torch new felt onto rotten boards. If your roof has been leaking, the old chipboard decking will have lost its structural integrity. I strip it back to the joists and install 18mm OSB3 (Oriented Strand Board), which is engineered to handle structural loads and resist moisture.
If you are dealing with an uninsulated outbuilding that has reached the end of its lifespan, you can find exactly what goes into a professional upgrade on my garage roof replacement service page.
Stop Guessing: Get an Instant Online Estimate
Roofing shouldn’t be a mystery, and you shouldn’t have to deal with tradesmen hiding their prices or pushing you into unnecessary upgrades. Now that you understand the technical reasons behind your garage roof felt failure, you can skip the usual industry runaround.
Instead of waiting weeks for a callback or a vague quote, you can use the free online calculator directly on my website. Simply input the rough dimensions of your garage, and in 30 seconds, you will receive an exact, instant price estimate for the materials, labor, and proper disposal of your old roof. If the numbers make sense, we can then arrange a free site survey to confirm the exact structural requirements.