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Roof Design

Unsuitability of Magnesium Oxide (MgO) building boards

As you will be aware through our Blue Notes, at the end of 2018 changes were made to the Building Regulations requiring external wall materials on buildings that contains flats, hospitals, residential care premises and student accommodation above 18 metres in height to be European classification Class A1 or A2.

This has resulted in the use of some relatively new type of building boards, commonly known as MgO (Magnesium Oxide) board, being used as either sheathing or as a backing board to render systems.

The NHBC have raised concerns that some of the products they have come across do not have suitable verification of performance and that similar products are known to have failed overseas, and specifically the NHBC has received reports from Denmark and other countries of defects in walls built using MgO building boards, typically as either sheathing or as a backing board to render.

Until such time as these issues have been resolved, and Radmat have conducted compatibility tests with specific manufacturers MgO products, it is our belief that they are not suitable for use with our waterproofing systems and are not acceptable for Warranty.

Cement Particle Building boards are proven as a suitable substrate for Radmat waterproofing systems and are available with European classification Class A1 or A2 and BBA Certification. Where a sheathing or render system backing board is required these products should be used and are acceptable for Warranty.

The full NHBC statement can be read using the link below, but the key parts of the statement are detailed below.