How to Price a Felt Roof: Labour, Materials and Margin Guide

Quick Answer: UK felt flat-roof installation typically costs £60-110/m² supply and fit for a 3-layer torch-on system, or £40-70/m² for a 2-layer pour-and-roll on smaller jobs. For a typical 25m² garage or extension roof, expect £1,500-2,800 supply and fit. Felt is the budget option vs EPDM (£55-95/m²) and GRP (£65-110/m²) — comparable on small jobs, less competitive on larger ones, with shorter lifespan (15-25 years vs 30+).

Summary

Built-up bitumen felt roofing — the traditional 2-layer or 3-layer torch-on system — has been losing market share to EPDM and GRP for two decades but still has a place in the UK market. It's competitive on small jobs (garages, porches, dormers), accepted by Building Control everywhere, and most roofers have the kit to fit it. The margin is reasonable if priced correctly and disastrous if you under-quote the prep work or the access.

This guide is for the general roofer or builder quoting felt jobs as part of a wider package, or as a standalone replacement. It covers the system options, productivity rates, fire-safety controls (which apply to torch-on work and are tightening), and the margin structure that makes felt a profit-margin product rather than a race-to-the-bottom commodity.

For alternative coverings see flat roof materials for a full comparison and flat roof extension pricing guide for whole-extension pricing.

Key Facts

Quick Reference Table

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Roof size 2-layer pour-and-roll 3-layer torch-on EPDM equivalent (compare)
10m² porch £450-700 £600-900 £650-950
15m² small dormer £600-900 £900-1,300 £950-1,400
25m² typical garage £900-1,500 £1,500-2,200 £1,500-2,400
40m² medium extension £1,500-2,300 £2,400-3,500 £2,400-3,800
60m² large extension £2,200-3,500 £3,500-5,500 £3,500-5,800
100m² commercial unit £3,500-5,500 £5,500-8,500 £5,500-9,500

Pricing for supply and fit on a prepared deck. Add 30-60% for full deck replacement, insulation overlay, or upstands and detailing on complex shapes.

Detailed Guidance

Cost components

A felt roof job has six cost components:

1. Strip-out (existing covering, repair deck) — varies hugely
2. Deck replacement / repair
3. Insulation (warm roof spec)
4. Vapour control layer
5. Intermediate and cap sheet (the felt itself)
6. Detailing — upstands, outlets, drips, soakers

The pricing trap is quoting "supply and fit" of the felt only and absorbing the rest. On a 40m² strip-and-recover, the strip-out and deck repair can easily be 30-40% of the job cost. The customer sees the felt going on; you see the days of stripping nails out of plywood.

System choice

Three mainstream systems for new flat roofs:

Pour-and-roll 2-layer (gas-torch alternative) — bitumen heated in a kettle, poured onto deck, felt rolled into it. Cheap, fast, two layers minimum. Lifespan 12-18 years. Now uncommon for new work due to fire risk and inconsistent finish but still seen on garage replacements.

Torch-on 3-layer — gas torch melts the bitumen backing of each layer onto the substrate. Industry standard for quality felt installation. Vapour control layer + intermediate layer + mineral cap sheet. Lifespan 20-30 years with quality felt and good workmanship.

Self-adhesive 2-layer cold-applied — peel-and-stick felt; no flame; good for fire-sensitive sites (over timber, near combustibles). Higher material cost but no hot works permit needed. Lifespan 18-25 years.

The torch-on 3-layer system is the default for new work where access allows. Self-adhesive is the right answer where insurer or fire-risk constraints rule out hot works — increasingly common since the Grenfell-era tightening of insurer hot works clauses.

Decking — the foundation of a good felt roof

Felt is only as good as the deck it's bonded to. Inspect carefully before quoting:

A 25m² job that looks straightforward at first glance often reveals 30-40% deck replacement once the old felt comes up. Always include a contingency line for deck replacement — "£X/m² for deck replacement found necessary on opening up" — or you'll absorb the cost.

Falls and ponding

Minimum fall per BS 6229:2018 is 1:80. This is barely adequate — water creeps slowly on a 1:80 fall and any local depression causes ponding. Best practice 1:40 (25mm per metre run), achieved with firring strips (tapered timber) ripped from 47×100 or larger timbers.

Direction matters: falls run towards outlets and gutters, never towards parapets or abutting walls where water will pool. On extensions joining an existing house, the fall is away from the house.

Ponding (standing water 24+ hours after rain) is the classic warranty failure. It accelerates UV breakdown of the cap sheet and causes vegetation growth. If the existing roof shows ponding before you strip, factor in firring strip rebuild — £20-40/m² in material and time.

Detailing — where felt jobs win or lose

The flat field of felt is straightforward. The details are where workmanship shows:

Each detail takes time. A 25m² roof with 1 outlet, 1 skylight and 2 wall abutments has roughly half a day in detail work — that's £180-250 in labour alone. Price it.

Hot works fire safety

Torch-on work is a fire risk. Recent insurer position has tightened:

Public liability insurance must specifically cover hot works. Many roofers find their policy excludes torch-on work or requires named applicators. Confirm before quoting.

For fire-sensitive sites (timber frames, listed buildings, occupied buildings) self-adhesive cold-applied is the right system. Higher material cost but eliminates the hot works risk entirely.

Productivity rates

Realistic productivity for a competent two-person team:

Task Rate
Strip existing 2-layer felt 30-60m²/day
Strip existing 3-layer + insulation 20-40m²/day
Replace decking 12-22mm OSB 25-40m²/day
Insulation overlay (warm roof) 40-70m²/day
Vapour control layer + intermediate felt 60-100m²/day
Cap sheet (mineral finish) 60-100m²/day
Detail work (per outlet/upstand/abutment) 1.5-3 hours each

Use a labour day rate of £200-280 per person for the South-East, £170-230 elsewhere. Materials are the cheaper part of a felt job — labour is typically 60-70% of total cost.

Worked example: 25m² garage roof replacement

Customer has a single-skin block garage, existing felt roof past life (water ingress, ponding visible). Strip and re-cover with 3-layer torch-on.

Scaffold (1-day) + skip (8-yard)                          £550
Strip existing felt + dispose                  0.75 day  £210
Inspect deck — 8m² replacement needed
  WBP 18mm ply 8m² × £40                                  £320
  Replace deck                                0.5 day    £140
Apply firrings to correct ponding              0.5 day   £140
  Firring timber + screws                                 £80
75mm PIR insulation 25m² × £25                            £625
Vapour control layer (perforated felt) + intermediate
  felt + cap sheet (3-layer system)
  Materials 25m² × £18 felt                              £450
Apply 3-layer felt                              1 day    £400
Lead drip edge + metal flashings + 1 outlet
  Materials                                              £220
  Labour                                       0.5 day   £140
Final inspection + clean down                  0.25 day  £70
                                                        -----
Subtotal direct cost                                    £3,345
Overhead (12%)                                          £401
Profit (28%)                                            £1,049
                                                        -----
Quote (excl VAT)                                        £4,795
                                              (~£190/m² inc strip)

This is a mid-market quote. Same job in 2-layer pour-and-roll: roughly £3,200-3,800. Same job in EPDM: roughly £3,600-4,400 (EPDM materials are more expensive but install is faster, no hot works).

Margin traps

  1. Deck replacement underestimated. Open up the corner of an old felt roof before quoting; estimate the % deck replacement and price it in writing as a contingency.
  2. Hot works insurance gap. If your PL excludes torch-on, you're trading uninsured. Check before any torch-on job.
  3. Ponding ignored at quote. Inheriting ponding without firring rebuild means it'll fail again in 8-12 years. Either price the firrings or document in writing that you've inherited the problem.
  4. Outlet count under-counted. Walk the roof and count outlets, upstands, and abutments — each one is detailing time.
  5. Skip not big enough. A 50m² strip plus old insulation is at least 6-8m³ of waste. That's not a 4-yard skip.
  6. Skin contact with hot bitumen. Serious burn injuries are common in trade — PPE up to elbow, never work in shorts.

Frequently Asked Questions

How long does a felt roof actually last?

Quality 3-layer torch-on, well-installed: 25-30 years. Budget 2-layer pour-and-roll: 12-18 years. Lifespan is hugely dependent on installation quality and roof exposure — south-facing roofs UV-degrade faster than north-facing.

Is 1:80 fall really enough?

It's the minimum allowed and it ponds easily. Quote 1:40 if at all possible — costs slightly more in firrings but dramatically reduces ponding risk and warranty calls.

Can I felt over an existing felt roof?

Sometimes — if the existing felt is sound, flat, and dry. More often it's not, and "over-laying" turns into a temporary fix that adds weight, hides problems, and fails inside 5-7 years. Strip and re-cover is the right answer most of the time.

What's the difference between mineral and smooth cap sheet?

Mineral cap (slate-chip finish) is UV-protected, walkable in moderation, and standard for visible roofs. Smooth cap is used where a screed or finishes will go on top (terraces, green roofs) — needs UV protection from above.

Can felt be used on a 0° (truly flat) roof?

No. BS 6229 requires minimum 1:80. A truly flat felt roof will pond, accelerate UV degradation, grow vegetation and fail. If the existing structure is dead flat, firring strips are essential.

Why has insurance got harder for torch-on?

Several large commercial fires in 2018-2022 were attributed to torch-on hot works. Insurers responded by tightening hot works clauses, requiring permits, fire watch, named operatives, and excluding higher-risk substrates (timber frame buildings). Many roofers have shifted to self-adhesive systems as a result.

Is felt cheaper than EPDM?

On very small jobs (under 15m²) — marginally yes. On medium jobs (20-50m²) — broadly comparable. On larger jobs — EPDM often wins because of faster install and longer life. The "felt is cheap" reputation is outdated.

Regulations & Standards