Torch Felt Roofs: My Straightforward Homeowner’s Guide to Doing It Once and Doing It Properly

What I Really Mean When I Say “Torch Felt Roof”

When customers ask me about a torch felt roof, they usually mean any flat roof that’s been installed with a gas torch and bitumen felt. In practice, that can range from a solid, long‑lasting system to something that starts blistering within a couple of winters.

In my 18 years on the roof around Brighton, Hove, Worthing and the rest of Sussex, I’ve seen every version of torch-on felt you can imagine – from perfect detailing that still looks tight after 20 years, to cheap overlays hiding rotten decking underneath.

So in this article I’m not going to repeat the usual sales talk about products. Instead, I’ll walk you through how I personally think about a torch felt roof: where it makes sense, when it doesn’t, and how I design and install it so you’re not back on the phone to me in three years’ time.

When a Torch Felt Roof Is the Right Choice – And When It Isn’t

If you ask me, I’ll tell you straight: torch-on felt is still one of the best all‑round choices for many Sussex flat roofs, but it’s not always the right answer.

Good situations for a torch felt roof

Standard flat roofs on garages, rear extensions, dormers and porches where you mainly need clean, robust waterproofing.
Simple shapes with a couple of upstands, maybe a skylight or two, where the detailing is straightforward.
Roofs exposed to coastal weather where you want a tough mineral finish that stands up to wind and salt air, as long as it’s installed properly.
Budgets that need value – you want something professional and long‑lasting, but not the price tag of a full warm-roof with high-end overlay membranes.

Situations where I might advise against torch felt

Fire-sensitive structures (for example, some timber-framed or very tight access areas) where open flame isn’t sensible. There are cold-applied options for those.
Complex roofs with lots of junctions where another system might cope better with movement or awkward detailing.
Roof terraces and balconies where you’re planning decking and heavy foot traffic – usually I’ll design a different build-up so the felt is protected.

If you’re not sure where your roof sits, the easiest way is to let me actually look at it. You can use my free roof inspection service in Brighton and Sussex and I’ll tell you honestly whether torch felt is suitable or not.

How I Design a Torch Felt Roof So It Actually Lasts

Most torch felt roofs that fail early don’t fail because of the material – they fail because of the design and preparation. When I’m planning a torch felt roof, I always think in this order: structure, falls, moisture, then felt. The felt is the last step, not the first.

1. Checking the deck: is the base even worth saving?

Before I torch a single roll, I check what’s underneath:

Timber deck – is it solid, or spongy underfoot? Any rot, delamination, or blackened areas?
Concrete deck – are there cracks, hollows, or areas that hold water after rain?
Existing felt layers – is it sensible and safe to overlay, or is it time to strip back to the deck?

Here is my honest advice: if the deck is moving or rotten, I won’t just skim over it. You might save a bit upfront, but you’ll pay for it twice when the new roof starts failing along with the old timber underneath.

2. Building in proper falls – so the water actually leaves

Torch felt is only as good as the water management under it. On a flat roof I always ask myself one question: where does every drop of water go?

I look for ponding areas – anything that still has puddles 24 hours after rain will give you problems later.
I design falls towards outlets – usually with tapered insulation or firring pieces on timber decks.
I keep an eye on gutter positions and heights – a great felt job is useless if the water has nowhere to go.

On many garage and extension roofs around Brighton and Hove, the fall is the main issue, not the felt. That’s why I often start by planning the cross-falls properly before I even think about which felt roll I’m unwrapping.

3. Managing moisture from below: cold roof vs warm roof

In my 18 years on the roof, I’ve noticed that a lot of flat roof condensation problems come from one simple issue: nobody thought about how the inside of the house breathes.

In basic terms, I look at two main build-ups:

Cold roof – insulation between joists, ventilation above it, then the deck and torch felt on top. This needs very good ventilation details or you’ll trap moisture.
Warm roof – insulation above the deck, then the torch felt system over that. This usually copes much better with modern, well‑sealed homes where airflow is limited.

When I survey your roof, I’ll look at the room below, any existing insulation, and how the building is used. A utility room or bathroom under a flat roof needs a different approach to a basic garage.

4. Then – and only then – I plan the felt system

Once I know the deck, falls and moisture strategy are right, I plan the actual torch-on felt build-up: typically a base layer, intermediate layer (if needed), and a cap sheet with mineral finish.

The key for you as a homeowner is this: if a roofer talks to you only about the top layer colour and not about the build-up below it, the design probably isn’t thorough enough.

The Torch Felt Roof Checklist I Use on Every Job

When customers ask me how they can tell if a torch felt roof has been done correctly, I break it down into a simple checklist. This is exactly how I judge my own work.

1. Is the deck solid and properly fixed?

No bounce underfoot.
No visible sagging between joists.
Screws or fixings spaced correctly and not pulling through.

2. Are the falls obvious and working?

When it rains, water heads clearly towards a gutter, outlet or hopper.
No large flat areas that form lakes after every shower.

3. Are the laps straight and fully bonded?

Rolls laid in straight lines, not wandering all over the roof.
Side laps and end laps fully bonded – no fish-mouths, blisters or soft spots.

4. Are the edges and upstands properly detailed?

Neat, tight corners – not big clumsy folds and ridges.
Clear termination points into walls, parapets or metal trims.
Any leadwork or flashings integrated, not just smeared with mastic.

5. Is the finish consistent?

Mineral surface even in colour and texture.
No burnt patches or bare bitumen showing where the torch has been over‑used.

If you want me to go through that checklist on your own roof, you can book a free roof inspection in Brighton and Sussex and I’ll walk you round it step by step.

Torch Felt Roofs on Different Parts of Your Home

Not every flat roof on your property behaves the same way. A torch felt roof over a heated rear extension has different demands to one over a simple garage or porch. Here’s how I look at each common area.

Garage roofs

Garages in Sussex are notorious for hidden problems – often the felt gets replaced over and over while the timbers quietly rot away beneath. When I’m asked to quote for a garage torch felt roof, I always check:

Condition of the joists and existing deck.
How the garage meets the house wall – a common leak point.
Any asbestos concerns in older coverings or soffits.

If you’re trying to budget for this, you can use my garage flat roof cost calculator for Brighton, Hove and Worthing to get a realistic ballpark before I even visit.

Rear extension roofs

On rear extensions, you’re usually dealing with a heated space directly underneath – a kitchen, living room or bedroom. That means I treat the design as part of the main house, not as an outbuilding. I’ll look closely at:

How the flat roof ties into the house wall and any existing cavity trays.
Whether a warm-roof build‑up makes more sense for comfort and condensation control.
Skylights, lanterns or roof windows, which all need careful detailing.

If you’re planning to upgrade or replace a rear extension roof, have a look at my rear extension flat roof service page where I explain the typical options I recommend.

Dormer flat roofs

Dormer roofs can be small but quite fiddly. You’ve usually got:

Abutments into the main pitched roof and tiles.
Lead flashings or soakers that need tying into the torch felt.
Limited access, which makes neat torch work more demanding.

On dormers, the junctions are more important than the field area. If those are wrong, you can end up with leaks that stain ceilings and run down inside walls. I cover these in more detail on my flat dormer roof repair and replacement page.

Porch and bay roofs

These might look minor, but because they sit over entrances and windows, they’re very visible when they fail. Poorly designed porch and bay felt roofs often show:

Ugly edges or trims that don’t suit the front of the house.
Mismatched levels into brickwork or render.
Water running straight down the front elevation because the falls weren’t planned.

When I re‑do porch roofs, I usually tweak the detailing at the same time so it looks sharper as well as staying watertight. If you’re thinking about this on your own home, you can see how I approach it on my porch flat roof repair and replacement page.

How I Protect the Vulnerable Edges of a Torch Felt Roof

In my experience, torch felt roofs don’t usually fail in the middle – they fail at the edges. So I spend a lot of time on what I call the “weak points” of a flat roof.

Upstands and wall junctions

Anywhere the roof meets a wall or parapet, I think about three things:

Height – the felt needs to come up high enough to stay clear of standing water and snow.
Termination – chase lines, flashings or cappings that lock the felt edge in.
Movement – how the building will move over time and whether that joint will crack or stretch.

Gutters and outlets

A lot of Sussex roofs fail right at the outlet, where leaves, moss and debris collect. When I’m doing a new torch felt roof, I:

Use proper pre‑formed outlets compatible with the felt system.
Detail the felt so water naturally finds the outlet instead of skimming past it.
Make sure there’s access for future cleaning – your roof may be perfect, but blocked gutters will still cause overflows.

If your leak is already coming through around a gutter or outlet, and you need it sorted quickly, you can use my urgent roof leak repair booking service in Brighton and I’ll prioritise you.

What My Process Looks Like If You Ask Me to Install a Torch Felt Roof

Because I’m an independent roofer, you always deal with me directly – from the first conversation to the final photo in your portal. Here’s exactly what usually happens when someone contacts me about a torch felt roof.

1. You get an idea of cost upfront

I don’t like vague pricing, and I know you don’t either. That’s why I use instant online calculators for common jobs, like garages, porches and rear extensions, so you can get a realistic idea before I even visit.

2. I carry out a proper site survey

On site, I’ll:

Lift what I sensibly can to check the deck.
Check the falls with a level, not just by eye.
Look at the room below to understand insulation and condensation risks.
Photograph existing problems so you can see exactly what I’m talking about.

3. I explain your options in plain English

I’ll usually give you a couple of options – for example, an overlay (if appropriate) versus a full strip‑and‑rebuild, along with the pros, cons and prices of each. No pressure, just facts so you can decide.

4. Fixed-price quote and clear scope

Once you’re happy with a plan, I give you a fixed‑price quote that doesn’t change halfway through unless we both agree on something extra that you’ve asked for. You’ll know exactly what’s included: deck work, insulation (if any), felt build-up, trims, and any related details like flashings.

5. Transparent build with a client portal

While I’m on site, you get access to a secure online portal where I upload daily photo logs of the work. That way, even if you’re at work or away, you can see the deck condition, how the layers are being built up, and what the final detailing looks like.

Honest Advice If You’re Deciding on a Torch Felt Roof

If you’re weighing up whether to go for a torch felt roof, here’s my honest advice based on nearly two decades on Sussex roofs:

Don’t choose purely on cost per square metre – choose on the quality of the design and the detail at the edges.
Ask your roofer how they’ll deal with falls and moisture – if the answer is vague, be cautious.
Make sure the deck is properly assessed – overlaying rotten timber is throwing good money after bad.
Think about how you use the space below – a kitchen or bedroom under a flat roof needs more thought than a basic shed.

If you’d like me to look at your roof and tell you, in plain language, what I’d do if it was my own house, you can book a free roof inspection and I’ll take it from there.

And if your flat roof is already leaking and you need to stop the damage quickly, use my priority emergency leak booking. I’ll diagnose the problem first, then give you clear options – from a solid temporary repair to a full torch felt roof done once and done properly.