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Hot Melt Roofing

A hot melt system is a form of roofing which has been used for centuries to help protect homes, businesses, and other structures from the elements. It has been used in many different regions of the world, including Europe and Asia. It has become increasingly popular in the United States in recent years due to its durability and cost-effectiveness.

The process was first used in flat roof waterproofing as it offered impeccable durability, cost-effectiveness, and performance, particularly in commercial areas. While there are countless other methods of roof waterproofing, when employed properly hot melt systems, can offer performance comparable to all the leading flat roof systems.

In this article, we will go over the basics of hot melt systems and some key considerations which must be kept in mind during the process. The goal is to help you understand the process and inform you of alternative waterproofing solutions.

What Is A Hot Melt Roofing System?

Hot melt is most commonly employed for inverted roof system waterproofing. It consists of a liquid-applied membrane, mostly asphalt or bitumen (also known as tar, which is heated until it melts and then applied directly to the surface of the flat roof).

The hot liquid directly goes on to a the prepared structural deck. It bonds together any existing materials on the roof’s surface, such as shingles or slate tiles, creating a moisture-resistant barrier. This type of roofing material is highly durable and can last for many years before needing repairs or replacement; if properly maintained, it can last for decades.

The use of hot melt roofs dates back to antiquity when it was first used by ancient cultures throughout Europe. In more modern times, this type of roofing became popularised in the late 19th century, with industrialisation allowing for the mass production of asphalt-based products. Hot melt roofs can be used on applications such as large inverted roofs, green roofs, concrete deck waterproofing, car parks, paving slabs, commercial offices, small residential terraces and roofs.

In the 20th century, advances in technology enabled manufacturers to produce higher-quality hot melt waterproofing productswhich could better withstand extreme temperatures and weather conditions. However, despite these advancements, hot melt was still primarily viewed as a low-cost alternative to more traditional types such as slate tiles or metal sheets.

Today’s hot melt roofing materials have come a long way since their introduction over 100 years ago. These materials are now formulated with additives like rubberised asphalt which make them waterproof. This enables them to easily stand up against extreme temperatures and weather conditions.

Furthermore, modern hot melt roofs can be made to resemble traditional materials such as wood shakes or slate tiles at much lower costs than those methods would require; this makes them an attractive option for homeowners who want an aesthetically pleasing finish whist staying within budget.

Benefits Of Hot Melt Roofing Systems

As mentioned above, hot melt waterproofing systems have a number of benefits which make it a great system for many applications. Among the most notable advantages are its affordability and dependability. This allows building owners to get the most out of their roofs without having to worry about costly repairs or replacements down the line.

It offers an oven-free formulation, better low and high-temperature resistance. Whilst also having the ability to be installed in extreme temperatures (including temperatures as low as -18°C).

In addition to being cost-effective, hot melt waterproofing is also incredibly long-lasting; depending on how well it is maintained, it can last for up to 30 years before needing any sort of repair or replacement.

Furthermore, since this type of waterproofing material for flat roofs can be made to resemble more traditional materials such as wood shakes or slate tiles, you won’t have to sacrifice aesthetics in order to benefit from its numerous advantages.

Another major benefit of hot melt roofing is incredibly easy to install. The entire process can be completed in a single day, and since the material is already melted when it’s applied, there won’t be any need for toxic chemicals or messy tools like with other types of roofing materials.

It is also quite quick to dry and is ready to be walked on right after installation. This means low curing time and, therefore, better results for flat roofs which are heavily used.

Project Types Suited To Using A Hot Melt Waterproofing System

Though hot melt roofing does offer some amazing benefits, there are still a few key things that roofers must keep in mind when taking on this type of project. First and foremost, you should always make sure that you’re working on the right project with this process and conditions.

For instance, applying hot melt roofing on a roof that hasn’t been prepared with concrete substrates or has frost on it may lead to poor adherence and a short lifespan of the roof. Direct application without proper preparations for timber roofs may result in timber burning and hence, reducing the durability therein.

Furthermore, using low-grade materials will not only have shorter lifespans but could also provide inadequate protection against moisture or extreme temperatures.

If you are not sure whether your roof can support the weight of an inverted roof system, hot melt roofing may not be the best choice. The minimum ballast weight (1) for the roof stands at 80 kg per square meter.

On the other hand, if there is a metal substrate on the roof, hot melt roofing may not be a suitable solution. The same is true when there is a hot boiler on site or if the previous roofing product was heated to 180°C before application.

Design & Installation of Hot Melt Roofs

When designing and installing a hot melt roof, architects must ensure that the proper steps are taken at each stage of the process. This includes properly assessing the building’s structure, selecting appropriate materials, and ensuring installation are done by experienced professionals.

It is important to note, a hot melt roof will require more structural support than many other types due to its weight; this should be factored into the initial design plans. Also, it is essential for architects to select only high-quality materials in order for the roof to last as long as possible without needing maintenance or repairs.

As mentioned above, an 80 kilogram per square meter is the minimum requirement for the hot melt roof, so make sure you check and design the supporting structure accordingly. When doing so, it is also important to take into account the following for better application:

• Wind uplift ballast calculations

• Drainage coefficients and requirement calculations

• U-value determination

• NBS roof specification and compliance (2)

• The general design of the roof.


Once done, installers must focus on the roof insulation installed. PIR insulation is known for its thermal efficiency and its generally warm design. However, installers are free to use the insulation they deep fit based on its performance. Vacuum insulation panels are known for their thermal performance and usage before the installation of hot melt roofs.


Sand and cement screeds are not recommended when trying to waterproof the hot melt, as they can create a potential fire hazard. A better solution is to use a vapour-permeable, asphalt-based membrane with high elasticity and flexibility. This will ensure that the roof remains waterproof and can stand up to extreme weather conditions without issue.

Many experienced roofing architects and installers use Permascreed (3) for the application of the hot melt as it is designed for mastic-asphalt applications. This is because it does not need to be primed, and it cures very quickly, like the hot melt roof.

Furthermore, it includes no water content, which means that when the hot melt touches the screed, it does not lead to bubbles or does not pose any threat to the applicators or the roof beneath it. However, it is important to note that the application of the Permascreed may be a bit costly because it requires a mastic asphalt installer.

Finally, it is critical for architects to work only with experienced professionals who have considerable experience installing hot melt roofs. Professional installers should have comprehensive knowledge of the materials used in this type of roofing system and will be able to properly assess the building’s structure prior to installation in order to ensure that everything goes smoothly from start to finish.

Guarantees & Maintenance of Hot Melt Roofs

Once the hot melt roof has been installed, the roof generally has a very long lifetime. It generally has a 20-25-year warranty, be it a dual signature (for products used and the installation process employed) or a single point (for products used and on-site workmanship).

The roof will require a bi-annual inspection for proper drainage and any cracks therein. If the gutters are kept clear, and the debris is swept away quickly, the roof can last the duration of its warranty quite easily.

Overall, hot melt roofs have proved themselves time and time again over the past years to protect properties from the harsh environment while providing lasting beauty at an affordable price point. The only requisite is proper maintenance.

Alternatives To A Hot Melt Waterproofing System

Amongst the best alternatives to a hot melt waterproofing system are liquid applied roofing and mastic asphalt roofing. Both these systems offer different advantages over hot melt which means for certain applications they may be a better choice. Liquid roofing systems are nearly always cold applied meaning it takes away all the safety concerns of hot works. It does this whilst still offering a completely seamless finish and an excellent ability to waterproof complex detailing.

Liquid systems also can be applied in nearly all weather conditions and allows excellent resistance to thermal movement. Another key plus for liquid waterproofing is how the skill demands of the contractor are low. This means you are reducing contractor risk when a building is waterproofed with a liquid applied system.

Mastic asphalt can also provide a seamless finish meaning lap joints can be completely avoided. A key benefit of using mastic asphalt over hot melt to provide a waterproofing layer, is mastic asphalt is carbon zero rated and completely recyclable. Additionally, asphalt spreaders are renowned for their high skillset due to the extensive training they undertake. By choosing asphalt you are assured of high quality contractor meaning the risk of a job not being carried out correctly is extremely low. 

Need Any More Information On Hot Melt Roofing?

We hope this blog post has helped you understand more about hot melt roofing. If you would like a quote for any upcoming project or would like to explore alternatives to hot melt roofing, you can contact us on 01277 375 511 or  get in touch via our contact form. One of our friendly team of experts will be delighted to help.