Last edited 31 Dec 2020

Advice for External Wall Insulation (EWI) systems with a render or brick-slip finish

External wall insulation (EWI) became notorious following the Grenfell Tower fire on 14 June 2017, when Celotex RS5000 thermal insulation was thought to have contributed to the rapid spread of the fire up the outside of the tower.

On 11 December 2017, the Department for Communities and Local Government issued Advice for building owners: External Wall Insulation (EWI) systems with a render or brick-slip finish.

The advice note was developed in consultation with the Department’s Independent Expert Advisory Panel and is intended for anyone responsible for the maintenance of buildings with EWI systems with either a render or brick-slip finish, particularly those over 18 m tall or in an exposed location.

The note states:

"Design calculations for EWI systems typically include safety factors to ensure that even where an installation is not perfect, or in the event that unusual circumstances occur (such as high winds), the system will remain safe... However, evidence submitted to Government suggests that in some circumstances these safety factors are being eroded by inadequate design (structural calculation methodologies) and / or poor installation."

"Where inadequate design and / or installation reduces safety factors, EWI systems are more vulnerable to: damage from high wind speeds; other installation defects such as poor water-tightness (which can lead to insulation becoming water-logged and heavier as a result); and variations in the design and installation quality of mechanical or adhesive fixings. These potential defects increase the risk of the EWI system becoming detached from the building and falling from height. This in turn poses risks to life safety. With render or brick-slip EWI systems there is a heightened risk of the render or brick-slip layer detaching from the insulation underneath where these defects are present."

Separate guidance, ‎Advice note for external wall systems that do not incorporate ACM, was also published on 11 December.

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