Before You Say Yes to Torch On Roofing Felt

When customers ask me whether torch on roofing felt is right for their flat roof, I never give a one-word answer. Torch on felt is a great system when it’s used in the right place, on the right deck, with the right detailing. It can also be a headache if those basics are ignored.

In this guide, I want to walk you through how I personally assess a roof before I recommend torch on felt. Think of this as me talking you through my thought process while we’re both standing in your garden looking up at your roof.

My Torch On Felt Checklist: The 6 Big Questions I Ask

Every time I’m called out to look at a flat roof, I run through the same mental checklist. Before I talk about brands, colours or guarantees, I ask myself six questions:

  • What condition is the existing structure in?
  • What type of deck am I working with (timber, concrete, OSB, old felt)?
  • How does the water actually leave this roof?
  • What’s happening at the edges, walls and around openings?
  • How will heat from the torch affect what’s underneath?
  • How do you plan to use this roof in real life?

Let me break those down in plain English so you can use the same thinking before you spend a penny.

1. Is Your Roof Structure Ready for Torch On Felt?

If you ask me for honest advice, I’ll tell you this: the best torch on felt in the world won’t save a rotten deck. Before I ever fire up a torch, I check the structure properly.

What I Look For in the Deck

  • Soft patches underfoot: If the roof feels spongy when I walk it, that usually means the decking is damp or rotten.
  • Visible sagging: A dip in the middle often tells me the joists are struggling or the boards have been wet for a long time.
  • Old chipboard: On older extensions and garages I still see chipboard. Once that gets wet, it swells and crumbles – not a good base for a heat-applied system.

When customers ask whether I can “just go over the top”, my answer depends on what I find here. If the deck moves or crumbles under a screwdriver, I won’t cover it up with felt and hope for the best. I’d rather show you photos in my client portal and explain exactly what needs replacing.

2. Choosing the Right Torch On System for the Job

Not every torch on felt job is the same. In my 18 years on the roof, I’ve learnt that matching the system to the roof use is just as important as the brand.

Typical Setups I Use

  • Simple garage or shed roof: Usually a two-layer system on a sound timber deck – ideal for garages, side lean-tos and basic outbuildings.
  • Rear extension or kitchen roof: I’m looking at insulation, vapour control and proper detailing because warm air from inside meets cold air outside.
  • Dormer or bay window: These need neat detailing where felt meets tiles or slates, plus attention to lead flashing and wall junctions.

If you’re unsure what category your roof sits in, I’m always happy to talk it through and, if needed, book a free roof inspection in person so we’re both looking at the same thing on-site.

3. How Torch On Felt Handles Water – Falls, Drains and Outlets

When customers show me photos of “mysterious flat roof leaks”, nine times out of ten the issue isn’t the felt itself – it’s the way water is (or isn’t) being directed off the roof.

What I Check Before I Recommend Torch On Felt

  • Is there a visible fall? Even flat roofs should have a slight slope. If water just sits in the middle for days, the deck is constantly under stress.
  • Where does water go? I look for gutters, outlets and downpipes that actually make sense for the roof size and shape.
  • Are outlets choked? Leaves, moss and old mastic around outlets are common leak points.

On some projects, especially larger rear extensions, I’ll recommend adding better falls or reshaping the deck slightly before installing new felt. There’s no point putting a quality torch on system over a design that guarantees standing water from day one.

4. Details That Decide Whether Torch On Felt Will Last

If you ask me what really separates a five-year roof from a twenty-year roof, I’ll tell you straight: it’s the detail work. Not the big open area in the middle – the corners, edges and upstands.

Areas I Spend the Most Time On

  • Upstands against walls: Felt should come up the wall to the correct height and either tuck under existing flashings or link neatly into new lead.
  • Parapets and firewalls: These need proper capping, especially in older Brighton and Hove terraces where damp can creep into neighbouring walls.
  • Edges and drip trims: This is where wind, water and gravity all meet. A lazy edge detail is usually where a “cheap job” starts failing first.

Before I agree that torch on is the right choice, I mentally run through how I’ll deal with each junction. If there’s no sensible way to seal an area with felt and torches – for example around delicate timber cladding or certain rooflights – I’ll tell you and suggest an alternative approach.

5. When I Avoid Using a Torch – Safety First

Torch on felt involves using an open flame. Used properly, it’s perfectly safe. Used carelessly, it’s a fire risk. I never ignore that.

Situations Where I Adapt the Method

  • Timber cladding or fascias right on the edge: I take extra care or use cold-applied methods near exposed timbers, plastic cladding and uPVC.
  • Old, dry timber decks: On some older roofs, especially garages and lean-tos, the timber is extremely dry. I’ll often use a safer technique or partial bonding rather than blasting heat into every joint.
  • Over certain insulations: Some insulation boards don’t like direct flame. In those cases I use a separating layer or different build-up to keep everything safe and stable.

When I survey your roof, I’m not just thinking about waterproofing – I’m also thinking about what’s underneath and how heat travels through it. If I feel there’s any risk, I’ll say so and suggest another way.

6. Matching Torch On Felt to How You Use the Roof

Not every flat roof is just a lid to keep the rain out. In Sussex I regularly see rear extensions and balcony roofs that double up as outdoor spaces.

Common Use Cases I See Locally

  • Basic weatherproof lid: Garages, utility rooms or outbuildings where you just want it dry and low-maintenance.
  • Above living spaces: Kitchens, lounges and bedrooms where insulation, condensation control and noise matter.
  • Balconies and terraces: Roofs that you actually walk on, with decking or tiles on top.

For simple garages, a straightforward torch on system is often ideal. For balconies and roof terraces, I might still use torch on felt as the waterproofing layer, but I’ll design it to work under decking or a terrace system so the felt itself isn’t taking the foot traffic.

How I Decide Between Repairing or Replacing Torch On Felt

When customers ask me, “Can you just patch it?” I look at a few key signs before I answer. I’m not interested in taking your money for a repair if I know it’ll fail in a year.

When a Repair Can Make Sense

  • Isolated damage: One clear puncture, a slipped flashing, or damage around a single outlet.
  • Relatively young roof: The rest of the felt still looks sound, with no widespread cracking or blisters.
  • Solid deck underneath: No movement or softness under the damaged area.

When I Recommend Full Replacement

  • Multiple leaks: If water is finding its way in at several points, the system is usually at the end of its life.
  • Widespread crazing and cracks: This tells me the felt has dried out and is simply too aged to rely on.
  • Rotten decking: If the structure is compromised, patching the top layer is a waste of your money.

On every job, I document what I find with photos and talk you through the options, including a fixed-price quote so you know exactly where you stand before any work starts.

What Torch On Felt Means for Day-to-Day Maintenance

A well-installed torch on felt roof doesn’t need constant attention, but it’s not completely “fit and forget” either. A few simple habits will help you get the maximum life from it.

What I Recommend You Do Each Year

  • Keep outlets clear: Clear leaves and debris from gutters, outlets and around any rooflights.
  • Visual check after storms: Have a quick look from a safe vantage point for any lifted edges or loose trims.
  • Don’t drag heavy items over it: On balcony roofs, use protective pads under planters and furniture.

If you ever notice staining on ceilings or walls below a flat roof, don’t ignore it. A small leak caught early is always cheaper and easier to deal with than a long-term hidden one.

How I Work If You Ask Me to Look at Your Torch On Felt Roof

If you decide you’d like me to assess your existing felt roof or quote for a new one, here’s how I handle it from start to finish.

1. Initial Conversation and Rough Costing

First, I’ll ask you a few simple questions: age of the roof, what’s underneath, and whether you’ve noticed any leaks or damp. From there, I can often give you a broad idea of cost brackets so you know whether it’s likely to be a repair, a partial replacement, or a full new system.

2. Free Site Visit and Honest Assessment

On-site, I’ll inspect the roof, check the deck where possible, look at all edges and joints, and work out how water currently drains. I’ll take clear photos so I can show you exactly what I’m seeing instead of you having to take my word for it.

3. Fixed-Price Quote and Clear Scope of Work

Once I’ve seen everything, I’ll put together a fixed-price quote. No “plus VAT surprises”, no open-ended extras. The quote will spell out what I’m going to do, what materials I’ll use, and how long it should realistically last if it’s looked after sensibly.

4. Full Transparency While I’m On the Roof

During the job, I document the work with daily photo updates so you can see the deck condition, the build-up of layers, and the finished detailing. Everything from schedule to invoices and warranties is stored in your client portal so you’ve got a proper record for the future.

My Honest Take on Whether Torch On Felt Is Right for You

After 18 years on Sussex roofs, I still rate a well-installed torch on felt system very highly – especially on garages, rear extensions, dormers and bay windows (as long as the structure underneath is sound and the detailing is done properly).

Where it isn’t right, I’ll tell you. That might be because the roof is better suited to another material, because access is too tight for safe torch work, or because of the way you want to use the space. My job isn’t to sell you a product – it’s to make sure your roof keeps the weather out and doesn’t become a recurring problem.

If you’re standing in your kitchen right now looking up at a stained ceiling and wondering what’s going on above it, you don’t need to guess. Ask me to come and have a look, and I’ll walk you through exactly what I’d do if it were my own roof – step by step, with no pressure and no hidden catches.