When customers ask me about “felt roofing felt”, they’re usually trying to work out one of two things:

  • Is the old grey/green mineral felt on their roof still good enough?
  • Or do they need to upgrade to a modern torch-on felt system?

In my 18 years on the roof around Brighton, Hove, Worthing and across Sussex, I’ve worked with every type of roofing felt you can think of – from brittle 1970s shed felt to high-performance SBS torch-on systems I install on garages, dormers and rear extensions today.

Here’s my honest, no-fluff guide to roofing felt: what it is, the different types, how to tell what you’ve got on your roof, and when it’s worth upgrading rather than patching.

What “Roofing Felt” Actually Is (Not Just the Cheap Shed Stuff)

When people say “felt”, they often imagine flimsy shed roll from the DIY shop. That’s one version of felt – but it’s not what I use on proper flat roofs.

In roofing, “felt” usually means a sheet membrane made from:

  • A base layer – often polyester or glass fibre
  • Bitumen – the black waterproof layer
  • A top finish – mineral granules or a smooth finish

The quality difference between cheap felt and high-performance torch-on felt is massive. If you ask me, I’ll tell you straight: a modern 3-layer torch-on felt system, installed properly, is a completely different animal to the old single-layer mineral felt you see cracking on old garages.

The Main Types of Roofing Felt You’ll See in Sussex

Let me break down the types I most often see when I climb onto roofs locally.

1. Old Style Mineral Felt (Usually on Garages and Sheds)

This is the stuff I strip off more than anything else.

  • Typically one or two thin layers
  • Hard, brittle feel when it ages
  • Granular (stony) surface, often faded grey or green
  • Joints are often poorly lapped or lifting

These systems might have lasted 10–15 years at best when first installed. By the time I get called out, they’re usually 20+ years old and long past their design life.

2. SBS Torch-On Felt (What I Recommend for Most Flat Roofs)

This is what I install on most garages, dormers, extensions, porches and bay window roofs around Brighton and Hove. It’s not the cheap stuff – it’s a high-performance membrane designed to flex and cope with movement.

  • Multi-layer system – usually 2 or 3 layers, including underlay and a mineral cap sheet
  • SBS-modified bitumen – stays flexible, less likely to crack
  • Heat-welded joints – using a torch to fuse the laps together
  • Available in different finishes – including mineral colours or smooth for capping

If you want more detail on the type of flat roofing work I do with torch-on felt, you can have a look at my main flat roof services page here: flat roof repair and replacement (SBS torch-on felt in Brighton & Hove).

3. Breather Felt Under Pitched Roof Tiles

Different type of “felt”, different job entirely.

This is the membrane under your roof tiles or slates. Its job is to:

  • Stop wind-driven rain getting into your loft
  • Allow moisture from inside your house to escape
  • Support any slipped tiles until they’re fixed

If you’ve been told your “felt is perished” on a pitched roof, that’s this membrane they’re talking about – not flat roof felt. I explain this service in more depth here: roof batten and breathable felt replacement.

How to Tell What Type of Felt Is on Your Roof

When I turn up for a survey, the first thing I do is identify exactly what’s already on your roof. You can do a basic version of the same from the ground or a safe window view.

Look at the Surface

  • Rough, stony, faded surface – likely older mineral felt
  • More even, newer-looking granules – probably a newer torch-on mineral cap sheet
  • Smooth, painted-looking finish – could be a cap sheet used for cappings or details

Check the Edges and Upstands

  • Thin, sharp edges that look like they could snap – older cheap felt
  • Thicker build-up, visible layers at the edge – multi-layer system (usually torch-on)
  • Neatly formed upstands against walls – generally a sign of a more modern installation

Tell-Tale Signs of Torch-On Felt

On a torch-on felt roof you’ll often see:

  • Slight bitumen bleed along laps (dark shiny lines where sheets connect)
  • Consistent lap width (usually 80–100mm side laps)
  • More solid, “rubbery” feel if you lightly tap with a knuckle

Old Mineral Felt vs Modern Torch-On Felt: Is It Worth Upgrading?

Here is my honest advice: once old mineral felt starts cracking and patching becomes a yearly event, it’s usually cheaper in the long run to upgrade to a proper torch-on system instead of paying for endless repairs.

Where I Still See Old Mineral Felt Letting People Down

  • Single garages – especially on 1960s–1980s houses
  • Porch flat roofs – often bodged over and over
  • Bay window roofs – exposed to driving rain on seafront houses
  • Small rear extensions – where the cheapest option was chosen years ago

If you want to play with some real numbers before you even speak to me, you can use my online calculators for different flat roof types:

All of those pages use the same approach: instant ballpark pricing online, then a free site survey if you want a fixed quote.

The Life Expectancy of Different Roofing Felts (My Real-World View)

Manufacturers love to quote big numbers. I prefer to tell you what I actually see out on the roof.

  • Cheap single-layer felt: 5–10 years if you’re lucky and it’s reasonably sheltered
  • Basic older multi-layer felt: 10–15 years, often cracking by 20 years
  • Modern SBS torch-on felt (3-layer, installed properly): 20+ years is realistic, and I’ve seen good systems still fine after 25

Of course, exposure makes a difference. Seafront properties and very exposed roofs will always age faster than a sheltered garage between two houses.

Where Felt Roofing Fails First (And What That Tells Me About the Installation)

In my 18 years on the roof, I’ve noticed that with felt systems, the weak points are nearly always:

  • At laps and joints
  • Around upstands and walls
  • At drip edges and outlets

When I inspect a leaking felt roof, I’m not just looking for obvious holes. I’m looking at how the system was built in the first place.

Poor Overlaps

Laps that are too small, not properly bonded, or running the wrong way with the fall will always cause trouble. On a good torch-on felt job, laps are generous and fully welded.

Bad Details at Upstands

This is where I see a lot of DIY or “cheap” jobs fail:

  • Felt just cut off against a wall and siliconed (temporary at best)
  • No proper chase or termination bar into brickwork
  • Loose or missing lead flashing over the felt

If your flat felt roof runs into brickwork and the detailing is poor, it’s worth looking at my dedicated service for this type of work here: professional lead flashing repair and installation.

Edges and Drips

On properly detailed roofs, the felt should:

  • Form a neat drip edge into the gutter
  • Have solid support underneath (no sagging)
  • Be well sealed around outlets and downpipes

Old felt that has sagged between joists often starts to crack and pond water. At that stage, it’s usually time to think bigger than just patching one spot.

Felt vs Other Flat Roofing Options: My Straight Opinion

Homeowners often ask me whether felt is “old fashioned” compared to rubber (EPDM) or fibreglass (GRP). Here’s how I explain it on site.

Where Felt Still Makes a Lot of Sense

  • Roofs with lots of shapes and details – dormers, bays, L-shapes, awkward junctions
  • Situations where I need to layer and build up around walls/parapets
  • Balconies and terraces with extra detailing under decking

For balconies and roof terraces, I usually design a system where the felt is your main waterproof layer, then decking sits above it. If you’re thinking about that kind of project, have a look here: balcony and roof terrace waterproofing and composite decking.

When I Don’t Recommend Cheap Felt at All

I won’t install the thin, DIY-style felt sheets you see piled up in builders’ merchants. They simply don’t last well enough for me to put my name to them. If cost is your main worry, use my calculators to see the real difference between a cheap stopgap and a decent torch-on system – you might be surprised how close they are over the life of the roof.

How I Design a Torch-On Felt Roof That Actually Lasts

Every roof is a bit different, but there’s a simple process I follow when I’m replacing old felt with a new system.

1. Check the Deck

If the timber deck under your felt is rotten or spongy, I’ll show you photos on my client portal and talk you through options. There’s no point putting new felt over a rotten deck – it’ll fail early and you’ll have paid twice.

2. Choose the Right Build-Up

Depending on your roof, I might suggest:

  • A 2-layer system for smaller, less exposed roofs
  • A 3-layer system for larger or more important roofs (like rear extensions over living spaces)
  • Extra insulation if you’re losing a lot of heat through that area

3. Sort the Edges and Upstands Properly

This is where the long-term success lives or dies. I spend a lot of time on:

  • Chasing felt and lead correctly into brickwork
  • Making sure water runs where it should
  • Setting correct falls where possible
  • Using proper cappings on parapet walls

If you’ve got boundary walls or parapets that keep getting damp, you might find this service relevant: firewall and parapet felt capping.

Should You Repair or Fully Replace Your Felt Roof?

This is probably the main decision people struggle with. Here’s the way I walk customers through it on site.

It Might Still Be Worth Repairing If:

  • The felt is generally sound and flexible
  • Leaks are isolated to one obvious defect (like damage from a tradesperson’s ladder)
  • The roof isn’t that old, but a detail was done badly

It’s Usually Time to Replace If:

  • The felt is cracking in lots of places
  • You can see exposed base layer or patches everywhere
  • The deck feels soft underfoot
  • Patch repairs have already been done multiple times

If your felt roof is already leaking and you’re worried about damage inside the house, use my priority booking service: Brighton urgent roof leak repair booking. I’ll stabilise the situation first, then we can talk calmly about repair vs replacement.

What You Can Expect Working With Me on a Felt Roof Project

The roofing industry has a reputation for vague pricing and disappearing quotes. I do things differently.

Instant Online Estimates

Before I even come out, you can use the calculators on my site to get a realistic, no-pressure price range for garages, extensions, porches, bays, balconies and more. No signup tricks, no hidden catch.

Free Site Survey and Fixed-Price Quote

If the estimate looks sensible, the next step is a free roof inspection. I’ll measure up properly, check the condition of your existing felt and deck, and talk you through options. You can book that here: book a free roof inspection in Brighton & Sussex.

After that visit, I send you a fixed-price quote. No vague “day rate” guesses. What I quote is what you pay, unless you ask me to change the spec.

The Client Portal

Once the job starts, you get access to a secure online portal where you can:

  • See the schedule and key dates
  • View daily photo updates of your roof as I strip and relay the felt
  • Download invoices, guarantees and documents

Most of my clients are at work while I’m on the roof. The portal means you still see exactly what’s happening every day.

How Roofing Felt Fits Into the Bigger Picture of Your Roof

Felt is just one part of your roof system. When I’m on site, I always look at how it connects to everything else:

When to Call Me Out to Look at Your Felt Roof

You don’t need to wait for brown stains on your ceiling before doing something. I’d suggest getting me in for a free inspection if you notice any of these:

  • Cracks or splits starting to appear in the felt
  • Granules washed away, exposing a black or dull base layer
  • Ponding water that sits for days after rain
  • Felt lifting at edges or around walls
  • Moss growth in the middle of the roof (often means standing water)

When I visit, I’ll take clear photos, explain exactly what type of felt you have now, and give you straight advice: patch, upgrade soon, or replace now. No pressure, no scare tactics.

If you’re in Brighton, Hove, Worthing or anywhere nearby in Sussex and you want a clear, honest opinion on your felt roof, you can start here: book a free roof inspection. I’ll bring 18 years of experience – and I’ll tell you exactly what I’d do if it were my own house.