Torch-on, cold-applied or self-adhesive bitumen membranes compared
Updated 23 October 2026 · SEO Dons Editorial
This guide compares the four ways bitumen membranes are bonded on commercial roofs. It is for owners and specifiers weighing up proposals. The fire rating of the finished roof is a separate question, covered in the BROOF(t4) guide.
How is each method applied?
| Method | How the layers are bonded | What the sources say |
|---|---|---|
| Torch-on | A gas torch is used to install the membrane | Soprema calls it the most popular method and says it requires the substrate to be clear of fire hazards or combustible materials |
| Hot-bonded, sometimes called pour-and-roll | Bitumen is heated in a boiler and used as the adhesive | IKO describes its bonding bitumen as hot-applied and loaded into a bitumen boiler. HSE notes LPG is widely used with bitumen boilers |
| Cold-applied adhesive | A bitumen adhesive bonds the layers | IKO says its adhesive allows total bonding of felts without hot bitumen or flames |
| Self-adhesive | The membrane has a self-adhesive underside, and laps are often sealed with hot air | Bauder and IKO describe systems where laps are heat-welded, with no naked flame |
BS 8217:2005, which BSI lists as current, gives recommendations on selecting and combining reinforced bitumen membranes and applying them to flat and sloping roofs. It covers torch-applied and self-adhesive membranes by name, and says its recommendations for new roofs also apply to overlays, subject to confirming that the existing construction is suitable.
When does the fire rule decide the method?
NFRC’s Safe2Torch guidance, which it says supports specification writers in meeting CDM 2015, sets the test. Where any fire risk has been identified, or cannot be ruled out, the relevant parts of the specification must default to solutions that do not use a torch. If an area is later shown to be safe, for example on uncovering it during refurbishment, the specification can revert to torch application if all parties agree.
The manufacturers checked list what raises the risk. Soprema names a timber roof deck, timber upstands, expansion joints filled with combustible fillers, hanging tiles, lantern rooflights and membrane roofs adjoining a pitched roof. Bauder adds abutments to cladding, slates or thatch, and dry leaf debris. Both describe a flameless zone of at least 900 mm around such details, which Soprema attributes to Safe2Torch. Bauder says the zone is marked out so that no naked flame work happens within it.
That allows mixed methods on one roof. Bauder gives two routes for torch application: the construction has nothing combustible in it, such as a concrete deck, or the combustible detail is fully encapsulated with a self-adhesive underlayer welded by hot air before a torched cap sheet goes on. Ask for a plan marking the flameless and torch zones. The hot works guide covers permits, fire watch and what insurers expect.
What do weather, substrate and detailing change?
- Weather. Limits are product-specific. IKO’s page on its reinforced bitumen systems says reliable installation in colder conditions depends on ambient temperatures remaining above 5°C. The pages checked give no limit common to all cold adhesives, so read the data sheet for the named product.
- Dry substrate. Soprema says many systems need a completely dry substrate, and that a gas torch is the quickest drying tool. Safe2Torch also covers drying out roofs, so a membrane laid without a torch can still involve one unless drying methods are specified. Soprema lists dry rags, wet vacs, mops and hot-air blowers as alternatives.
- Insulation facing. Soprema says a self-adhesive membrane requires an insulation layer with a different facing, so insulation boards change with the method.
- Vertical details. Where a bitumen membrane cannot be activated with warm air, Soprema’s default recommendation is a liquid solution. See liquid-applied roofing.
- Speed. Soprema describes self-adhesive technology as quick to install and says SBS bitumen takes less heat to install than the plastomer (APP) range. The pages checked give no independent programme comparison, so none is given.
How do manufacturer warranties and insurers fit in?
Manufacturer cover is written for a named system. IKO says all its reinforced bitumen systems are installed exclusively by IKO-approved and registered contractors, and that its cover extends to materials, design and installation. Soprema says its capsheet choice determines the warranty length and that its longest warranty is available only for complete system build-ups. Bauder says only its approved contractors are trained and certified to install its products. The bonding method belongs to that system, so ask the manufacturer to confirm in writing that the proposed method, including any hybrid zones, is covered. The page on manufacturer cover explains how it is structured.
For insurers, the FPA says hot work should only be carried out if there is not a safer alternative, and its list of hot work examples includes roofing and the use of hot air guns. Ask the insurer in writing whether hot-air welding of self-adhesive laps counts as hot work under the policy.
Which method suits which building?
| Situation | What the sources point to | Ask for |
|---|---|---|
| Occupied building, concrete deck, nothing combustible in the construction | Bauder says torch application can be safe here. The FPA says hot work should only be done where there is no safer alternative | Insurer’s written view, permit and fire watch |
| Timber deck, upstands or fillets | Safe2Torch default applies. Soprema lists timber decks among areas NFRC guidelines discourage or forbid hot works | Self-adhesive or cold-applied method, correct insulation facing |
| Non-combustible field area with combustible details | Hybrid: encapsulate details by hot-air welding, or use the 900 mm zone | A plan marking torch and flameless zones |
| Older or heritage building, construction unknown | Risk cannot be ruled out, so the Safe2Torch default applies until uncovering shows otherwise | Survey of edges and details, agreement in writing, conservation requirements raised early |
| Complex vertical details | Soprema defaults to a liquid solution where warm-air activation is not possible | Liquid detailing in the specification |
| Overlay of an existing roof | BS 8217 applies to overlays subject to the existing construction being suitable. Bauder says its Airtech system can be a two-layer overlay on a thermally reliable roof | Survey first, including the asbestos position of old felt |
The built-up felt and reinforced bitumen page describes the system itself and the felt roof repair guide covers patching. To compare proposals for your own roof, you can send roof details through the form on the refurbishment page.
Sources
- NFRC, Safe2Torch (checked 22 October 2026)
- BSI, BS 8217:2005 Reinforced bitumen membranes for roofing (checked 22 October 2026)
- HSE, Process fire risks; FPA, What is a hot work passport? (checked 22 October 2026)
- IKO, reinforced bitumen systems, IKOpro felt adhesive and Easy Melt bonding bitumen, for facts about IKO products (checked 22 October 2026)
- Soprema, waterproofing, no-flame solutions, torch-on alternatives, roofing felt overview and SOPRASTICK, for facts about Soprema products (checked 22 October 2026)
- Bauder, detailing near combustible materials and Airtech system, for facts about Bauder products (checked 22 October 2026)
Common questions
Is torch-on felt banned on commercial roofs?
The sources checked describe a specification approach, not a ban. NFRC's Safe2Torch says to default to solutions that do not use a torch where a fire risk is found or cannot be ruled out, and Bauder says torch application can be safe where nothing combustible is in the construction. The insurer's conditions may be stricter than either.
Is self-adhesive felt really flameless?
The field membrane often is, but the systems from Bauder and IKO seal laps by hot-air welding, and Soprema's SOPRASTICK has an overlap that is partly self-adhesive and partly torchable with flame or hot air. Ask exactly what heat source is used at laps and details, and whether the insurer treats it as hot work.
Can a cold-applied system be laid in winter?
Only within the limits set for the named product. IKO's page on its reinforced bitumen systems says reliable installation in colder conditions depends on ambient temperatures remaining above 5°C. The pages checked give no limit common to all cold adhesives, so ask for the data sheet.
Does the bonding method change the manufacturer's warranty?
Cover is issued for a named system installed by an approved contractor, and Soprema says the capsheet chosen determines the warranty length. Treat a change of bonding method after tender as a change to the specification and ask the manufacturer to confirm cover in writing.