Flat Roof Insulation Unravelled

May 30 2018 0comment

Flat Roof Insulation Unravelled

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When it comes to a flat roof, one of the most important considerations is which type of insulation to use – and this is just as true for roof refurbishment projects as it is for new roof installations.  The main purpose of insulation is to maintain a comfortable temperature within the building envelope and this is measured through the thermal conductivity (lambda value) of the material used.  The lower the lambda value of the insulation material, the more difficult it is for heat to pass through.  Thermal performance will be enhanced and a reduced thickness can be used to achieve the desired U-value (overall thermal performance) of the roof in question.

There are several options available in the UK for insulation materials for use in flat roofing, with a wide range of thermal conductivity values and other technical benefits.  These include:

  • Polyisocyanurate Insulation (PIR) – with a typical thermal conductivity score of 0.021 – 0.027 W/m.K, PIR offers the most effective thermal conductivity of any commonly used roofing insulation product.  It’s well suited to applications in which specifiers need to achieve high levels of thermal performance with lightweight, slim construction.
  • Extruded Polystyrene Insulation (XPS) – with a typical score of 0.029 – 0.036 W/m.K, is a low cost option that offers excellent compressive strength.  This is a great choice for applications where there is likely to be a requirement for significant roof access or additional weight such as a green roof.
  • Encapsulated Vacuum Insulation Panels (VIPs) – with a typical score of 0.009 W/m.K.  VIPs are a recent addition to the market here in the UK.  They have a microporous core enclosed within a gastight envelope which enables them to offer impressive thermal conductivity.   The innovative range of new products includes VIPs encapsulated within strong PIR board, eradicating the requirement for a protection layer or for separate insulation overlay to be installed above the VIPs, saving on time and costs.  VIPs are ideal for use in problem areas where the construction depth needs to be kept to a minimum whilst providing the required level of thermal performance.  Typical applications for VIPs include balconies or roof terraces above warm spaces where the encapsulated VIPs offer a reduced construction depth without sacrificing effective thermal conductivity, providing a level transition between internal and external spaces.

Because flat roofs have to be properly drained which has led some manufacturers offering tapered design services with the insulation factory cut to match the design.  This means that boards with a scheme template can be delivered to site, which streamlines the installation process whilst making sure that the surface of the roof drains adequately. 

There is no particular best insulation option for all roof applications and the best solution for a specific roof depends on the performance and design requirements of the individual building.  When regular roof access is required, a stronger solution is recommended and, in order to ensure the safety of those who need to work on plant and machinery on the roof, a demarcation system which identifies a safe route to work areas should be considered.

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