Some like it hot……but not us!


In an earlier blog on our website, we explained the reasons behind our policy of only offering cold-applied flat roofing systems.  Traditional flat roofing systems have been based on hot-works – bitumen boilers and flame torches – but at AAC Waterproofing we took the decision many years ago to eliminate the use of hot-work from our roofing projects for reasons of safety to people, avoiding fire damage to property and all of the subsequent and prolonged claim and counter-claim negotiations which follow a serious roof fire.

In this blog, we will look in more detail at the specific aspects of roofs which are most at risk from hot-work and in turn highlight the reasons for our ‘cold-is-best’ roofing business policy.

Hot Works Safety Procedures

The safety of hot bitumen and flame torch work on roofs have always had to be managed, which relies on operatives following the correct safety and handling procedures at all times.  Unfortunately, this doesn’t always happen and human error or worse, neglect, creeps in on occasion.  This can occur for example when a roofing operative leaves a flame torch alight while going off for a tea break.  The flame can heat up and ignite nearby materials, causing a roof fire.  This has happened on a project where the flame torch was left alight during a tea-break and near to a stack of polyurethane insulation boards stored on the roof.  The insulation caught fire and subsequently caused a whole roof fire.

Making the roof fire situation worse, of course, is the actions of the fire brigade in putting out the fire, and the consequential water damage to the building interior below.

Combustible Materials

But assuming all safety procedures are being followed avidly by the operatives more discreet risks are often present on flat roof buildings.

A common roof configuration is to have a flat roof intersecting with a pitched roof, where the pitched roof eaves overhang the flat roof at a low level.  Torching to the abutment under the pitched roof eaves is fraught with danger as there will usually be fine dry dust or organic matter in the concealed eaves which can catch fire from sparks from the torching.  This may not be immediately apparent as the dust can smoulder for some time before igniting fully, which may well be after the roofing contractors have gone home.  This is the reason why there will usually be a ‘fire-watch’ hour at the end of the day’s work when no hot-work is done, but the site observed for signs of hidden fire.

More than one roofer has been unpleasantly surprised by smoke and flames emanating from a concealed wasps nest under eaves or even within a cavity wall, where torching to an abutment near weep holes can allow sparks to do their damage.

It has even been known for the fire to travel along a wood-fibre tilt fillet at an abutment, behind the newly torch-applied bitumen felt flashing.

It is not only the roof edge details which are at risk from torch-applications.  Any form of a timber deck is susceptible to ignition from torches during the installation of the vapour control or base layer of bitumen felt.


The bitumen felt the industry has recently instigated its ‘Safe2Torch’ policy for hot works on roofs.  Under this policy it is incumbent on the specifier – manufacturer/system supplier or roofing contractor – to assess the roof for features at risk of fire from flame guns and to specify alternative materials for these areas, such as self-adhesive felts or liquid-applied waterproofing.  This may mean specifying only cold-applied materials for the whole roof, or maybe allowing the use of torch-on materials to the field area, away from fire-risk details, while switching to cold-applied materials for the areas at risk from the torch such as abutments to combustible materials or under window cills, roof lights, overhanging eaves or cladding.  Even if the cladding itself is non-combustible there will usually be a cavity behind where fire can roam free.

It is also common under these safe-specification methods to install a self-adhesive vapour control layer to combustible decks, have insulation bonded in cold adhesive and a self-adhesive underlay, but with the cap sheet being torch-applied.

Eliminate Fire Risks

All of these actions and procedures help to reduce the risk of fire to a bare minimum, by eliminating the torch from most of the flat roof build-up components.  However, the torch is still present on-site meaning that there will always be some residual risk.  At AAC Waterproofing, we prefer to follow the first rule of Health & Safety and eliminate the risks entirely where possible.  Our flat roofing installation services do not require hot works.  We do this by only offering cold-applied waterproofing systems for the whole roof area.

Single-ply thermoplastic membranes, such as Protan and Sarnafil, are adhesively bonded or mechanically fixed and jointed with hot air, which is intrinsically safe.

Our Prelasti EPDM prefabricated synthetic rubber sheets go one step further by being completely fabricated in our quality controlled workshop, so don’t even require site jointing.

Our cold-applied liquid waterproofing system takes care of awkward details efficiently and provides a homogenous waterproofing membrane across the whole roof.

We will be happy to discuss how we can install your flat roofing project without the worry of fire-risk from the works.

“Some like it hot”………..but we prefer cold!