Technical Update: Polyroof VIP Insulation

There are many different types of thermal insulation materials available to Contractors and Specifiers.

These include Polyisocyanurate (PIR), Stone Wool, Expanded Polystyrene (EPS), Extruded Polystyrene (XPS), Cellular Glass and Vacuum Insulated Panels (VIP).

The main factors influencing the selection of insulation type and thickness of insulation are as follows:

  • Details, upstand and threshold heights  
  • The required U-value  
  • Compressive strength and suitability for foot traffic  
  • Fire resistance (as part of the system)  
  • Acoustic performance  
  • Cantilever and free span capability  
  • Suitability for intended method of attachment.  
  • Compatibility with other roofing components.  
  • Aesthetics and quality of finish

Common Issues with Upstand and Threshold heights

This article tackles one of the most common issues encountered in flat roof design – Low upstand and Threshold Heights.

Care should be taken to ensure that the any design meets British standards and building regulations. In accordance with BS6229:2018 this requires a minimum 150mm upstand height above the roof finish. However, the roof design will also need to meet the U-Value requirements in accordance with Approved Document L (conservation of fuel and power). This occasionally causes issues particularly when upstand heights are restricted and when considering the use of conventional insulation boards such as PIR or Stone wool. Therefore how does VIP insulation assist?

Vacuum insulated panels (VIP)

Vacuum insulated panels (VIP) have a very low thermal conductivity (typically at least three times more thermally efficient than the materials listed above). Therefore a much thinner board can be used to obtain the same U-Value. However, it should be noted they cannot be cut on site, or mechanically fixed or their performance is ruined. The panels therefore have to be installed to a precise scheme design, with infills of conventional insulation.

Polyroof VIP Insulation is supplied with a vacuum core and a tough high density outer layer to protect the core which otherwise could be easily damaged. The boards are so thin that they can be used in renovation for flat roofs and terraces where limited space is available.


  • In new builds it can avoid height issues and lower construction costs 
  • In renovation it can avoid increasing the height of the upstands, avoid adapting windows, doors, while keeping the thermal design highly efficient. 

Further information and next steps

Polyroof Technical services offer a service to provide bespoke VIP schemes for your project. To obtain a scheme or make an enquiry click here.

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