Magnesium oxide building boards

6 December 2018

NHBC has become aware of a relatively new type of building board being used in the UK, commonly known as MgO board. Some of the products we have come across do not have suitable verification of performance and we understand that similar products are known to have failed overseas.

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. We are working with a number of stakeholders to understand the exact cause of the failures.

To achieve satisfactory long-term performance across a range of critical functions, building boards must be suitably durable and able to withstand the environmental conditions that they are likely to be exposed to, including humidity. We understand there are variances in the types, quality and manufacturing process of MgO boards, which may have a significant effect on how they perform in practice when exposed to humid conditions.

As a reminder, where products with a critical function are used on NHBC registered sites, they should hold suitable verification of their performance. Typically this can be achieved through compliance with a British Standard or via satisfactory assessment undertaken by a technical approvals’ authority (independent third party certification) acceptable to NHBC, such as the BBA or KIWA. 

As there is no British Standard for MgO boards, the process for these products to be accepted for use on NHBC registered sites must be via independent certification.

There are a number of MgO boards available in the UK that do not comply with a relevant British Standard or hold satisfactory certification, and therefore do not comply with the guidance in NHBC’s Standards.

Next steps

As of 1st January 2019, NHBC will only accept MgO boards under the following conditions:

  1. The boards hold independent third party certification, which includes specific reference to compliance with the NHBC Standards.
  2. The certification should be awarded to the board as an individual building component or specifically assessed for durability when it is a component of a certificated rendering system.
  3. Boards are fixed with suitable stainless steel fixings as specified by the board supplier.
  4. The boards are not to be used below DPC level.
  5. Where used as sheathing, the boards are protected from precipitation during construction by the use of a breathable membrane.

We have been in discussions with the certification bodies and a number of MgO board manufacturers who are working to provide us with assurances that the boards available in the UK will not give rise to the same problems as those seen in Denmark.

The MgO boards listed below are the ones currently acceptable to NHBC, however please note that this list is subject to change as the situation develops.

MgO boards currently accepted by NHBC are:

Building Adhesives: BBA certificate 17/5428 

Resistant Building Products: BBA certificate 15/5255

You need to

  • Talk to your MgO board supplier or contractor to ensure that any MgO boards being supplied hold current certification.
  • If you are intending to use a substitute board, ensure that the replacement meets NHBC’s Technical Requirements either via compliance with a relevant British Standard or by independent third party certification.
  • Ensure that the board can provide a suitable level of performance across all critical functions, specifically in relation to the building it is being applied to and environmental conditions it is likely to be subjected to.