Government has ruled out the use of any material that does not have one of the top combustiblity ratings in buildings over 18m

The use of cross-laminated timber in buildings more than 18m tall appears to have been outlawed as the government reveals details of its combustible materials ban.

The amendment to Approved Document B has ruled out the use of any material within an external wall that does not have one of the top combustibility ratings, A2-s1, d0 or Class A1, with the exception of membranes, seals and gaskets. The document defines an external wall as “anything located within any space forming part of the wall”.

The changes to both the Approved Document B and Section 7 of the building regulations not only cover residential towers that rise more than 18m above ground, but will also need to be adhered to by those building student accommodation, care homes, sheltered housing, hospitals and dormitories in boarding schools.

While these changes could spell the end of CLT in resi towers, companies concerned about the ability to use rainscreen cladding systems when the ban came into affect have been heard, with the ban excluding membranes, seals, gaskets, fixings, sealants and backer rods.

Doors, windows and their frames are also exempt from meeting the combustibility rating requirements.

The new regulations mean that only the European classification class A2-s1, d0 or class A1 will be acceptable and that materials achieving limited combustibility cannot be deemed to meet the requirement using an alternative classification method.