The Technical Reality of Garage Roof Failures
When you need to re roof a garage, the two biggest frustrations are usually diagnosing why the old membrane failed and getting a straightforward price to replace it. Unlike complex residential extensions with intricate parapets, garage roofs are structurally standardized. Yet, after 12 years of inspecting outbuildings across Brighton and Hove, I consistently see them failing prematurely due to outdated materials, poor edge detailing, and coastal wind exposure.
Why Do Garage Roofs Leak?
Older mineral felt roofs are notorious for cracking under the strain of thermal movement. As the sun heats the roof, the timber deck expands and contracts. Traditional oxidized bitumen lacks elasticity, meaning it simply snaps under this structural tension. Furthermore, water ingress on garage roofs often starts at the drip edges due to capillary action—where water gets drawn backward beneath the poorly bonded felt—or from persistent ponding water caused by insufficient structural falls.
Because most outbuildings are uninsulated ‘cold roofs’, thermal bridging and severe condensation aren’t usually the primary culprits here. It is almost always material fatigue, UV degradation, or wind uplift peeling back failing flashings.
The Proper Process to Re Roof a Garage
To permanently solve the issue, I strip the roof right back to the structural timber deck. If the existing decking is rotting from long-term water ingress, I replace it with 18mm OSB3 boards to create a rigid, flat substrate. We then install high-performance SBS-modified bitumen (torch-on felt). The SBS (Styrene Butadiene Styrene) rubber additives allow the membrane to flex with the garage’s thermal movement without tearing or blistering.
Calculate Your Exact Price Instantly
Because garages are inherently straightforward structures that vary primarily in their square meterage, quoting shouldn’t be a drawn-out mystery. If you are planning ahead and want to know what it costs to re roof a garage, you don’t need to deal with pushy sales calls or wait weeks for a site visit.
I have built an online calculator directly on my website tailored to this exact standardized structure. You simply enter your garage’s length and width, and choose between a single-layer or a highly durable two-layer SBS felt system depending on your current budget. Because the variables are fixed, the price generated is highly accurate. You get your exact estimate instantly, without committing or even needing to pick up the phone. This is an excellent tool if you are just weighing your renovation options.
Use the calculator today to budget your project. Once you have your numbers and are ready to proceed, I will conduct a free site survey to verify the decking condition and lock in your fixed quote.