When to use a Hot Melt Roofing System

Here’s an introduction to hot melt roofing and structural waterproofing and some suggestions as to when you should consider hot melt for your flat roofing project.

What is Hot Melt?

Hot melt is a membrane that is applied as a hot liquid directly to a prepared structural deck to create a completely seamless, monolithic layer. It is suitable for use as the waterproofing layer most new build flat roofing applications, when covered by suitable protection.

The most common application of hot melt is as an inverted roof system, where the membrane is laid directly on the deck and insulation is laid on top, weighed down with ballast materials such as 20-40mm gravel or 50mm paving slabs. Hot melt inverted roofs have many benefits, not least that they can be completely flat.

SIG Design & Technology supply IKO PermaTEC Hot Melt, which was the first hot melt system to be manufactured in the UK.

When to Consider a Hot Melt Inverted Roof

So when is a hot melt roof the best choice for a flat roofing system? SIG Design and Technology design and supply the best solution for our customers’ waterproofing needs, which means choosing the most practical, cost effective system for their project. Here are some examples of when our clients choose hot melt.

1. Waterproofing a Concrete Deck

When you have to waterproof a concrete deck, hot melt is the simplest, swiftest solution, with no need to drill into the deck for fixing, fast curing times and no need for a separate vapour membrane. It is commonly used in projects from small residential terraces right up to the large inverted roofs of commercial offices and modern shopping centres. Recent installations include

• The Evelyn Grace Academy by Zaha Hadid
• Ravensbourne College by Foreign Office Architects
• St Johns Therapy Centre by Henley Halebrown Rorrison

More examples at the end of this article.

2. Designing a completely Flat Roof

It is best practice is for all flat roofs to have a fall to ensure good drainage. However designers often decide to for a variety of different reasons to have completely flat roofs, for example, when there is no space for falls to be incorporated into your roof design.

Most waterproofing systems require at least minimal falls to comply with codes of practice and BBA certification, but with hot melt no falls are needed and the roof deck can be completely flat. This can be particularly useful when planning considerations restrict building heights. IKO PermaTEC Hot Melt is certified for use in these conditions.

3. Pressure of Time or Reducing Cost of a Flat Roof

When you need to save on the cost of tapered insulation or screed to falls, hot melt provides an opportunity to remove the need for tapers and screeds altogether, making the solution more competitive. On a tight programme, a fast curing hot melt inverted roof system saves installation time. As hot melt can be installed at temperatures as low as -18 Celsius, winter installation is also possible.

4. Complex Roof Layout and Penetrations

Floating Plinth Detail – Click to download Design Guide

If your new flat roof has a complex layout where falls are difficult, or if you need to install HVAC equipment, or the roof has several penetrations, hot melt can simplify the installation.

As well as removing the need to design in falls, an IKO PermaTEC hot melt roof can be simply detailed to allow for a wide variety of upstands, penetrations and structural connections.

For example, installing roof top plant can be problematic due to the risk of cold bridging. With a hot melt inverted roof, a floating concrete plinth can be installed on top of the insulation, removing any chance of cold bridging by placing the plant completely outside the membrane/insulation system.

5. Designing a Flat Roof for a Long Life

The membrane in an inverted roof is covered and therefore protected from the elements, footfall and mechanical damage throughout its life. With hot melt, the membrane is also fully adhered to the deck, so that if it does become damaged, water cannot migrate between membrane and roof structure and repairs are relatively straightforward.

IKO PermaTEC hot melt is formulated to last the lifetime of the building on which it is installed, so with simple maintenance, you don’t need to allow for replacement costs. It is even possible to upgrade the insulation at a later date without disturbing the weatherproofing.

Some points to note:

1. Installing hot melt roofing should be carried out by an experienced, certified contractor. Have your inverted roof installed by an IKO PermaTEC trained and qualified roofing contractor.
2. The structural deck should be capable of supporting the weight loading of an inverted roof system, which would usually be between 95kg/m2 and 140kg/m2.
3. The roof should be designed to incorporate adequate drainage, overflow and consider thermal requirements and wind conditions.
4. The waterproofing system must be fully tested (usually electronically or flood test) for damage prior to the installation of the insulation and loading coat (ballast/pavers/green roof).

SIG Design & Technology in conjunction with IKO Plc can design your hot melt inverted roof for you as part of our supply service for IKO PermaTEC hot melt. Get in touch with us for details of our free service.

More Information

Visit our PermaTEC Hot Melt Pages for more information about the product

Example projects using PermaTEC system in their roofing: [Links to architects websites]

• The Evelyn Grace Academy by Zaha Hadid
• Ravensbourne College by Foreign Office Architects
• St Johns Therapy Centre by Henley Halebrown Rorrison
• Queen Elizabeth Hospital Birmingham by BDP Sheffield
• Granary Wharf Leeds by Carey Jones
• Casa Hotel Chesterfield by Carey Jones
• Westfield Stratford City by Fletcher Priest Architects

Download a brochure of Case Studies Here.

Download the IKO PermaTEC Hot Melt Design Guide.

Read about the environmental benefits of PermaTEC – including zero wrapper waste and low delivery mileage.

Contact us for advice on your project, or post a comment below with your questions.