BYL Group

Kingspan Insulation: Rise of the fall

Phil Heath, Technical Manager at Kingspan Insulation, outlines the importance of careful roofing design

The flat roof is a perennial construction favourite, but however simple the design may appear it is never without its challenges. Changes to the Building Regulations Approved Document Part L have increased the requirements for energy efficiency, along with increased pressure for long term performance. Then there are issues of fire safety, and the often neglected area of walkability. Meanwhile common problems llike water ponding, membrane failure and water penetration often raise their ugly heads.

One way of dealing with the ponding issue is to introduce a fall into a warm deck flat roof, and this is normally achieved in one of three ways: falls achieved by screed laid to falls; falls achieved by use of tapered insulation; or falls achieved by use of timber firrings under a plywood base.

Tapered insulation does not suffer from the two inherent disadvantages in the use of screeds, drying time and weight. A standard cement and sand screed dries out in approximately one month per 25 mm thickness, and weighs around 2000 kg/m3. The weight of a screed can have significant load-bearing implications and therefore impact on the design of a structure, while the length of time needed for it to dry could affect the build programme.

So is there a cost benefit in employing any of the three options? Kingspan Insulation commissioned an independent cost analysis from Davis, Langdon & Everest using three case studies to examine the economical aspects of the different methods. In all three case studies, the tapered insulation solution was shown to be the cheapest option.

The screeded screed laid to falls option came out at £5-6 per m2 more expensive than a tapered insulation solution, with timber firrings proving to be the most expensive means of achieving drainage falls. Having established that a tapered insulation system is the speediest, lightest and most cost effective solution, there are a number of different insulation materials that can be used for tapered roof projects. It is critical for these materials to perform if buildings and their services are to behave as designed. There is little point in taking steps to improve the thermal performance of our buildings if those measures do not then deliver, and the implementation of the Energy Performance of Buildings Directive will see performance under regular review.

The reality is that the inevitable foot traffic arising during the construction of a roof and in the course of normal maintenance can severely affect some insulants. Foot traffic can lead to permanent degradation and compression of some insulation materials, which in turn could cause water ponding, membrane failure etc, the very problems specifiers want to avoid by introducing a fall in the first place.

Mineral fibre products can be vulnerable to both permanent partial collapse and water absorption, both of which can seriously degrade their thermal performance. Cellular plastics on the other hand are not susceptible to moisture, have a high resistance to compression and are capable of performing at a high level over the lifetime of the building.

However, durability is only one of the major issues that specifiers need to consider, there is also the question of fire safety. The Loss Prevention Certification Board (LPCB) standard LPS1181: 2003, is a large-scale insurer recognised ‘inapplication’ test that can offer a much more realistic insight into how a building will perform under fire conditions that the controversial Euroclass system of fire performance classification, which focuses on a very specific product quality, in this case their reaction to fire. LPCB approval also has the advantage of enhancing insurability. Kingspan Insulation is the first insulation manufacturer to achieve a Grade B listing to LPS 1181: 2003: Part I for a built-up external tapered roof system. The external envelope construction tested comprised a steel deck with insulation and single-ply membrane waterproofing system.

The LPCB approved products are manufactured using patented Nilflam® technology as standard, and are also FM (Factory Mutual) approved. Together, FM approval and LPCB approval to LPS 1181 represent two of the most respected and exacting fire performance standards in the world.

Kingspan Thermataper Systems are tapered rigid urethane insulation boards with FM and LPCB approval, designed for warm deck flat roofing applications. Using these products can not only achieve the requirements of the new Building Regulations/Standards, but could also yield a saving of up to 21 per cent over the cost of using alternative methods to create a fall in a flat roof for drainage purposes. Kingspan Insulation offers an extensive range of insulation solutions for both new-build and refurbishment projects. Specifiers, stockists and contractors are supported with a comprehensive and free technical advisory service. The Davis Langdon & Everest report is available on Tel. 0870 850 8333.