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Waterproofing and insulation: a perfect match

Waterproofing and insulation: a perfect match

By Richard Polling, group director MRC Group and board member of Thermal Insulation Products and Systems Association SA (TIPSASA)

It’s uncommon to hear about insulation, its properties and how to install it properly, especially when preparing to waterproof a roof. TIPSASA gives some tips on how to do it.

Does waterproofing go hand in hand with insulation?

There are many types of insulation available in the market place with a vast myriad of performance characteristics. The type and position of the insulation used in conjunction with a waterproofing system depends on whether the roof is to be considered a cold, warm or inverted roof.

A cold roof construction is one where the insulation is laid between the ceiling joists and not in the pitched rafters. This means that everything above the insulation is cooler than the living space. Warm, moisture laden air can permeate up through the ceiling. The roof space above the insulation needs to be ventilated to remove the damp air and therefore prevent condensation forming.

A warm roof construction is where the insulation is positioned into or above the main rafters forming a composite roof system. This form of construction is the main preference of insulating a waterproofed flat roof and the waterproofing system is laid above the insulation.

An inverted (or protected) roof construction is where the insulation is positioned above the waterproofing systems therefore providing long term protection of the waterproofing, while still offering insulation performance.

The required design performance, insulation system, ventilation and waterproofing products must be considered together to ensure the client’s brief is achieved for long-term performance.

Installing insulation onto a roof before waterproofing

Best practice in terms of the installation of insulation is dependent on the type of waterproofing system to be used above or below it.

There is a vast range of waterproofing systems from screw fix polyvinyl chloride (PVC) membranes, liquid applied coatings through to flame applied torch on membrane systems and – depending on which system is used – will dictate what type of insulation system will be considered to achieve the required thermal, fire and acoustic performance.

The insulation must provide a flat surface on which to apply the waterproofing. Therefore, the density of the insulation is important to consider when ensuring that the area to be waterproofed is firm enough to withstand the weight of the installation team. If the insulation is not at the correct density, then the waterproofed surface could show undulations that will cause water ponding conditions.

When installing waterproofing, what is best practice?

All the various waterproofing systems have a unique installation methodology with experienced contractors who install the systems. Most waterproofing contractors are experienced in the installation of the insulation and the associated waterproofing system. A compliant International Organization for Standardisation (ISO) system that incorporates from design, installation and maintenance will ensure that all aspects of the system are correctly installed for long-term performance, double checked by the manufacturer and the client.

Some challenges that insulation installers face

Some of the frequent challenges that any contractors face, is that in general insulation systems are manufactured to standard sizes, however most building design is bespoke, leaving the designer or contractor with the task of incorporating the standard modules into the building design. High levels of waste and additional tasks of cutting and supporting the insulation can drive installation costs higher.

In most cases contractors prefer to install inverted roofs as there is a structural surface to waterproof onto and then a simple exercise of laying insulation board above the waterproofing, which is ultimately covered with ballast. Rather than working retrospectively under the waterproofing system and trying to install insulation between rafters and non-standard centres.


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