Felt for Garage Roof – Why Modern SBS Torch-On Systems Outperform Old Felt
When I’m called out to leaking garages in Brighton, Hove, or Worthing, the problem is almost always the same: old mineral felt that has reached the end of its movement capacity. Traditional felt roofs simply weren’t designed for the thermal expansion and contraction we see in modern UK conditions, especially on exposed garage structures.
For garage roofs today, I consistently specify Tecnatorch SBS Torch-On Mineral Felt Charcoal because it behaves completely differently from the oxidised bitumen products used 30–40 years ago. It’s flexible, UV stable, and crucially, it can move with the structure instead of fighting against it.
Why Old Felt Systems Fail on Garages
Most garage roofs built in the 1980s and 1990s used basic built-up felt systems. These materials become brittle over time due to UV degradation and repeated thermal cycling. In Sussex, where coastal winds and salt exposure accelerate ageing, I often see:
- Surface cracking from thermal stress
- Blistering caused by trapped moisture and poor ventilation
- Splitting at joints due to capillary water ingress
Once this starts, water doesn’t just sit on the surface – it tracks through overlaps and penetrations, often damaging timbers before you even notice an internal leak.
Why SBS Torch-On Felt Performs Better
The key difference with SBS-modified bitumen is elasticity. The polymer modification allows the felt to expand and contract with temperature changes without fracturing. This is essential for garage roofs, which are typically uninsulated and exposed to rapid heat gain and loss.
Tecnatorch SBS Torch-On Mineral Felt Charcoal also includes a mineral cap sheet that provides UV protection, meaning the system doesn’t degrade in the same way older exposed felts do.
Two-Layer System Explained
When I install a proper garage roof system, I always use a two-layer build-up:
- Base layer: a smooth underlay that accommodates structural movement
- Cap sheet: a mineral-surfaced layer that protects against UV radiation and mechanical wear
This layered approach is critical. Garage roofs move. The timber deck expands and contracts daily, and a single-layer system simply cannot absorb that stress without splitting.
Installation Method – Why Torch-On Matters
The system is applied using a gas torch, bonding the bitumen directly to the prepared deck. This creates a fully adhered membrane with no loose laps or weak adhesive points. Done correctly, it eliminates wind uplift issues and reduces the risk of capillary water tracking between layers.
The quality of finish is also significantly better than cold-applied alternatives. A properly torched SBS system flows into joints, sealing them as a continuous waterproof barrier rather than a patchwork of glued seams.
Common Failure Points I Still See
Even with modern materials, poor installation causes most problems. The issues I regularly repair include:
- Inadequate substrate preparation leading to poor adhesion
- Incorrect detailing at wall abutments and upstands
- Single-layer installations used to cut cost
In many cases, especially on older garage blocks, I recommend a full replacement rather than patch repairs. If water has already entered the deck, the structure is usually compromised.
Professional Garage Roof Replacement
When I replace a garage roof, I treat it as a complete system – not just a surface layer. That includes checking timber condition, correcting falls for drainage, and ensuring all edge trims and flashings are mechanically fixed and sealed.
You can see typical project costs and options here: garage roof replacement overview and cost guide. For more complex flat roof structures, I also apply the same SBS torch-on methodology across extensions and outbuildings where movement is a factor.
Conclusion – Why I Specify SBS Felt for Garage Roofs
In practice, a garage roof isn’t just a waterproof lid – it’s a moving structure exposed to constant thermal cycling. That’s why I rely on SBS-modified systems like Tecnatorch. They don’t just cover the roof; they accommodate how the building behaves over time.
If you’re dealing with leaks, bubbling felt, or visible cracking, it usually means the system has already lost elasticity. At that point, a proper replacement is the only long-term fix. You can get an instant idea of cost and options using my online calculator, which gives a clear, no-obligation estimate in under a minute.