What People Really Mean When They Say “Felt Roofing”

When customers ask me about “felt roofing felt”, they’re often talking about two completely different things without realising:

  • The old-style, grey, gritty felt you see on tired garage roofs
  • The modern SBS torch-on felt systems I use on extensions, dormers and porches

On top of that, “felt” also gets used for the breathable underlay under your tiles on a pitched roof. So when you search online, you get a confusing mix of results.

In my 18 years on the roof around Brighton, Hove and Worthing, I’ve learnt that most problems with “felt roofs” are actually down to choosing the wrong type of felt in the first place, or not understanding what it can and can’t do.

Here is my honest, no-jargon guide to felt roofing materials, how long they really last, and how I decide whether to repair or replace when I’m standing on a roof in front of a customer.

The Different Types of Roofing Felt (and Where They Belong)

If you ask me, the biggest source of confusion is that people use one word – felt – for several very different products. When I visit your property, I’ll always start by working out exactly which of these we’re dealing with:

1. Old Mineral Felt on Flat Roofs (The “Shed Felt” Look)

This is the classic, older style felt you’ll see on many garage roofs and older extensions:

  • Usually grey or green with a gritty, mineral surface
  • Often laid in one or two layers with simple lap joints
  • Common on roofs from the 70s, 80s and 90s

Pros:

  • Cheap at the time of installation
  • Quick to put down

Cons:

  • Doesn’t cope well with movement – cracks and splits are common
  • Shorter lifespan, especially on south-facing roofs in Sussex sun
  • Joints are often the weak point and start leaking first

When I see this type of felt on a garage flat roof, I’m already thinking in terms of remaining lifespan, not just patching a single hole. If the whole surface is crazed and brittle, a local repair is usually just buying you time.

2. Modern SBS Torch-On Felt Systems

This is what I specialise in for most of the flat roofs I renew.

  • SBS (styrene-butadiene-styrene) modified bitumen – stays flexible
  • Normally installed in two or three layers
  • Joints are heat-welded, forming a continuous waterproof layer

Where I use it most:

Done properly, this type of felt system is nothing like old “shed felt”. It copes far better with heat, cold, and the natural movement of the building. That’s why I base my main flat roof replacement work around high-quality SBS torch-on membranes rather than the old mineral felt rolls you see in DIY stores.

3. Breathable Felt Under Tiles on Pitched Roofs

This is where the word “felt” confuses everyone even more.

On a pitched roof (with tiles or slates), the “felt” is actually a breathable membrane that sits over the rafters and under the battens. Its job is to:

  • Catch any wind-driven rain or snow that gets under the tiles
  • Allow moisture from inside the loft to escape
  • Work with vents and gaps to keep the roof space dry

So if you hear phrases like “the felt has perished under the tiles” or “you need new felt and battens”, that’s talking about a very different product to flat roof felt. I’ve got a dedicated service for full roof batten and felt membrane replacement when the underlay has completely failed.

How Long Does Felt Roofing Actually Last?

When customers ask me how long their “felt roof” should last, I never give a blanket number. It comes down to four things:

  • The exact felt product used
  • How it was installed (single vs multi-layer, torch-on vs nailed)
  • Roof design – falls, outlets and detailing
  • Exposure – sun, trees, seafront winds, foot traffic

Realistic Lifespans I See in Sussex

  • Old, basic mineral felt roofs: 10–15 years is common, sometimes less on very exposed garages.
  • Better quality multi-layer felt systems from the 90s/2000s: 15–25 years if they were installed properly.
  • Modern, high-quality SBS torch-on systems: 20+ years is realistic with the right detailing.

So when I’m standing on your roof, I’m not just asking, “Is it leaking?”. I’m asking:

  • What type of felt is this?
  • How far through its natural lifespan is it?
  • Would you be better off putting money towards a full upgrade rather than chasing leaks every winter?

Repair, Overlay or Full Replacement? How I Decide

Here is my honest advice: there is no single answer that fits every felt roof. But I do follow a clear process when I inspect a flat roof.

When a Simple Repair Makes Sense

I’ll usually recommend a repair if:

  • The felt is generally soft and flexible, not brittle
  • There’s one clear defect – a puncture, a lifted seam, damage around a pipe
  • The roof design is basically sound – it actually falls to a drain or gutter

That might mean a torch-on patch, re-forming a joint, or fixing local detailing. If you’re in a rush and the water is coming in, you can use my priority emergency leak repair booking to get into the system quickly.

When an Overlay is a Sensible Middle Ground

Sometimes the roof is tired but not completely gone. In those cases, I might suggest an overlay system:

  • The existing felt is dry, reasonably sound and firmly stuck down
  • I can safely improve the falls with tapered insulation or new boards
  • The extra weight is within what the structure can handle

Overlaying with a modern multi-layer felt system can give you many more years of life without the cost of a full strip back to joists.

When Full Replacement Is the Only Honest Option

In my 18 years on the roof, I’ve noticed that if you’re experiencing regular leaks in different areas, the felt is cracked all over, or the boards below are spongy, repairs are a false economy.

Signs I’ll point out to you on site:

  • Large areas of crazing and alligator cracking
  • Blisters everywhere, not just in one patch
  • Pooling water that never seems to drain after rain
  • Rotten decking boards – the roof actually moves under your feet

At that point, I’ll tell you straight: it needs stripping, new boards, and a complete new felt system. That’s where my fixed-price quotes and instant online calculators help, especially for things like garages and porches.

Key Details That Make or Break a Felt Roof

Even the best felt roofing felt will fail early if the detailing is poor. This is where experience really matters.

1. Upstands and Wall Junctions

Anywhere the roof meets a wall, parapet or chimney is vulnerable. I always look carefully at:

  • How high the felt is turned up the wall – it should be well above the finished roof level
  • How it’s sealed – is there proper lead flashing, capping, or just mastic?
  • Is the brickwork or render sound, or is water getting in behind?

On parapet walls, I often recommend proper felt capping to protect the top of the wall and stop damp tracking across into your ceilings.

2. Drains, Outlets and Gutters

Most leaks I deal with on felt roofs aren’t from a random hole – they start around outlets and edges. I check for:

  • Blocked outlets causing standing water
  • Felt not dressed properly into the gutter
  • Cheap plastic outlets that have cracked or shrunk

When I renew a roof, I don’t just swap like-for-like; I look at how the water actually leaves the roof and improve that if needed.

3. Movement and Foot Traffic

If you or other trades are regularly walking on the roof, I’ll tell you honestly: the system needs to be chosen and detailed for that.

  • Extra protection layers in high-traffic zones
  • Defined walkways to plant, aerials or roof lights
  • Stronger decking and better fixing patterns

This is especially important if you’re turning a flat roof into a usable space like a terrace or balcony. In those cases, I’ll steer you towards proper balcony and roof terrace waterproofing systems, not just standard felt.

How I Price Felt Roofing Work (No Guesswork)

The roofing trade has a bad reputation for vague pricing and “it’ll be about this much” quotes. I do it differently.

Instant Online Estimates

For common flat roof types – garages, porches, dormers and extensions – I’ve built simple calculators on my site. You enter a few basic details, and you get a realistic cost range straight away. No sales pitch, no commitment.

Free Site Survey and Fixed Quote

If you like the estimate, I’ll come out, get up on the roof, check the structure, measure properly and talk through options with you. After that, you get a fixed-price quote. The number you see is the number you pay, unless you specifically ask for extra work later.

Full Transparency While the Work Is Ongoing

Once the job starts, you’re not left guessing what’s happening up there. I use an online client portal where you can:

  • See the schedule and what stage I’m on
  • View daily photo updates of your roof
  • Download your invoice and any warranty documents safely

For a lot of my customers, that’s the first time they’ve ever really seen what’s under their old felt, and it helps you understand exactly what you’ve paid for.

When Should You Get Your Felt Roof Looked At?

If you’re not sure whether your felt roof is near the end of its life or just needs a bit of attention, here are a few signs it’s worth getting me out for a look:

  • Dark stains on ceilings that seem to come and go with heavy rain
  • Bubbles or blisters in the felt surface
  • Cracks showing the layer below, especially around edges
  • Standing water that’s still there a day after normal rainfall
  • Bits of gritty mineral surface in your gutters

You don’t have to wait for a disaster. If you’d like an honest opinion and a clear plan – whether that’s repair, overlay or full renewal – you can book a free roof inspection and site visit, and I’ll talk you through the options while I’m actually standing on your roof.

My Straightforward View on Felt Roofing

Felt roofing felt itself is not the villain – bad products, rushed installations and poor detailing are. A well-designed, properly-installed felt system can give your home decades of reliable protection.

If you ask me, the key is to:

  • Use the right type of felt for the job
  • Be honest about remaining lifespan when leaks start
  • Pay attention to outlets, edges and wall junctions
  • Keep you, the homeowner, fully informed at every stage

Whether you’ve got a leaking garage, a tired old extension roof, or you’re planning a new flat roof and want it done properly from day one, I’m happy to come out, take a proper look and give you a clear, fixed-price plan.