What Is Torch-On Roofing Felt?

Torch-on roofing felt is a type of waterproofing system made from bitumen (a petroleum-based material) that is reinforced with polyester or fiberglass. The “torch-on” part comes from the way it’s applied: roofers use a blowtorch to heat the underside of the felt until it melts slightly, then bond it to the roof surface.

This creates a seamless, watertight layer that’s tough, flexible, and long-lasting. Typically, torch-on felt is laid in two or three layers:

• Base layer – provides the first bond to the roof deck.
• Intermediate layer – adds strength and extra waterproofing.
• Cap sheet – the top layer, often finished with a mineral surface to resist UV damage and weathering.

The result is a roof covering that can last 15 – 25 years (sometimes longer with proper care).

Why Is Torch-On Roofing Felt So Popular?

If you ask three roofers why they recommend torch-on felt, you’ll probably hear three slightly different answers, but they all come back to the same truth: it works. Here’s why it continues to be a go-to choice:

• Proven durability – It resists tears, punctures, and weather extremes better than standard felt.
• Excellent waterproofing – The heat-bonded seams leave no weak spots for leaks.
• Low maintenance – Once installed properly, it requires very little upkeep.
• Cost-effective – More affordable than single-ply membranes or liquid coatings, yet still very robust.
• Versatility – Suitable for flat roofs, garages, sheds, porches, and even commercial buildings.
• Quick installation – Experienced roofers can install it efficiently, minimizing disruption.

For property owners, that combination of reliability and value is hard to beat.

How Torch-On Felt Is Installed

The process of installing torch-on felt is where craftsmanship really matters. A proper installation is the difference between a roof that lasts 20 years and one that fails in five.

Here’s a breakdown of how it’s typically done:

1. Preparation of the roof surface: The roof deck must be clean, dry, and stable. Old felt or debris is removed, and any rotten decking replaced.
2. Primer application: A bitumen-based primer is often brushed or rolled on to help the felt adhere more securely.
3. Torching and bonding: Using a propane gas torch, the roofer heats the underside of the felt until it becomes tacky. The felt is then rolled into place, pressing firmly to create a tight seal.
4. Layering system: The first and second layers are torched down, with overlaps sealed tightly. Finally, the cap sheet is applied, with mineral granules or a reflective finish to protect against UV damage.
5. Detail work: Flashings, corners, and edges are carefully sealed. These are the “weak spots” of any roof, so precision here is vital.

It’s skilled work. In fact, torch-on felt installation is not a DIY-friendly job, it involves open flames, heavy materials, and a need for real expertise.

Benefits Of Torch-On Roofing Felt

Let’s go a little deeper into the key advantages:

• Long lifespan – With 2 – 3 layers, it’s built to withstand decades of rain, frost, and summer sun.
• Resistant to pooling water – Flat roofs often struggle with standing water. Torch-on felt can handle this without quickly degrading.
• Tough against foot traffic – Great for roofs that need occasional access (like maintenance walkways).
• Fire-resistant top surfaces – Many cap sheets are designed with fire retardants, adding safety.
• A neat, professional finish – Mineral-surfaced sheets come in different colours, improving appearance.

Drawbacks You Should Know

No roofing system is perfect, and torch-on felt has a few downsides worth mentioning:

• Requires skilled installation – A poor job leads to weak spots, blisters, or leaks.
• Torching risks – The use of open flames means safety precautions are essential.
• Not as eco-friendly – Bitumen is a petroleum product, and disposal can be an issue.
• Limited “breathability” – Trapped moisture beneath the layers can cause problems if not installed correctly.

Still, when installed properly by professionals, these drawbacks are minimal compared to the benefits.

Typical Cost Of Torch-On Roofing Felt

Prices vary depending on roof size, access, and the number of layers, but here’s a ballpark for Ireland and the UK:

• Materials – €8 – €15 per m² (higher for premium mineral finish).
• Labour – €40 – €70 per m² installed, depending on complexity.
• Total cost – A typical single garage roof (20m²) might cost around €1,000 – €1,400.

Compared to other systems, torch-on felt usually comes out as one of the more affordable options while still delivering longevity.

Maintenance And Lifespan

Torch-on felt doesn’t demand much once it’s in place, but a little care goes a long way:

• Inspect the roof once or twice a year.
• Keep gutters and outlets clear of debris.
• Check seams, edges, and flashings for early signs of lifting.
• Trim back overhanging branches to prevent punctures.

With these simple steps, a felt roof can easily last 20+ years.

Torch-on roofing felt has been around long enough to prove itself. It’s durable, cost-effective, and delivers peace of mind against Ireland’s famously unpredictable weather. While newer materials exist, torch-on remains a trusted choice for homeowners, landlords, and commercial property managers alike.

If you want a flat roof system that strikes the right balance between reliability and affordability, torch-on felt is hard to beat. Just remember: the key is professional installation. Done right, it will protect your property for decades; done wrong, it can cause headaches.

So, if you’re weighing up your options, ask yourself: do you want a roof you never have to think about, or one you’ll constantly worry about? Torch-on roofing felt offers the first option, and that’s why it continues to be a favourite across Ireland and beyond.