Dealing with Garage Roofs: From Single Units to Large Blocks
Many calls I get in Brighton and Hove are about failing garage roofs. Often, it’s a simple case of an old mineral felt covering that has become brittle and cracked after years of UV exposure. But the real challenge, and something I have extensive experience with, is tackling entire rows of terraced garages. Whether you’re responsible for a single unit or a block of 20, the principles of diagnosing and fixing the problem remain the same, though the execution becomes more complex.
Technical Reasons for Garage Roof Failure
A leaking garage roof is rarely a surprise; it’s the result of predictable material degradation and design flaws. Here’s what I typically find on-site:
1. Aged Bitumen Felt and UV Degradation
The most common material on older garages is a simple roll-on mineral felt. Over 10-15 years, the sun’s ultraviolet radiation breaks down the bitumen, making it rigid. Thermal movement (the expansion and contraction from summer heat to winter cold) then causes this brittle material to crack, creating direct paths for water ingress.
2. Poor Drainage and Structural Sagging
Many older garage roofs were built with an insufficient ‘fall’ or slope. This leads to ‘ponding’—standing water that doesn’t drain away. This water not only adds significant weight, potentially causing the timber deck to sag, but it also accelerates the breakdown of the felt membrane, exploiting any tiny imperfection or weak seam.
3. The Terraced Garage Problem: Adjoining Details
On a terraced block, the weakest points are the joints between properties. A failure on your neighbour’s roof can easily lead to water tracking sideways and entering your garage. This often happens due to:
- Failed Upstands: The felt is not correctly turned up against the dividing party walls (or has slumped down over time).
- Porous Brickwork: Water soaks into unprotected brick party walls above the roofline and tracks down into the structure below.
- Seamless Membrane Failure: The original roofer may have created a poor seal or lap joint right over the dividing line between two garages.
The Modern Solution: A High-Performance System
My approach is not to patch, but to replace the failing system with one designed to last. The process for a proper garage roof replacement is methodical.
First, I strip everything back to the structural timber deck. This is non-negotiable as it allows me to inspect for any rot or weakness, which must be repaired before proceeding. Once the deck is sound, I install a modern, two-layer SBS-modified torch-on felt system.
This isn’t the brittle felt of the past. SBS-modified bitumen has rubber polymers incorporated, giving it excellent flexibility to handle thermal movement without cracking. For a terraced block, I create one continuous, seamless membrane across all units, meticulously sealing all upstands against party walls and ensuring every detail is watertight. This eliminates the risk of water tracking from one unit to the next.
Get an Instant Price for Your Garage Roof
Understanding the technical failure points is the first step. The next is understanding the cost. Now that you know what a proper, long-lasting installation involves, you can use my online calculator to get an instant, fixed price for your specific garage roof. There’s no need to wait for a site visit for an initial estimate; you can get a detailed quote in under 30 seconds.