Building regulations for external wall insulation
The short answer
In England, insulating more than half of an external wall (or more than a quarter of the whole building envelope) is renovating a thermal element, so the wall should be upgraded to 0.30 W/m²K where feasible and building control must be involved. Wales and Northern Ireland have their own regulations needing approval, and Scotland normally requires a building warrant for an external insulation cladding system.
England: renovating a thermal element
Renovation means adding a new layer to a wall or replacing an existing one, not just redecorating. The energy standards apply where more than 50% of a wall's surface, or more than 25% of the whole building envelope, is renovated, which covers almost any EWI job. For walls the target in Approved Document L is 0.30 W/m²K; if that isn't technically, functionally or economically feasible (a simple payback over 15 years), the wall should be improved to the best standard that is. Building control is notified and inspects or certifies the work.
Wales
Wales has had its own Building Regulations and Approved Document L since 2011, with similar principles for renovated walls. EWI needs building control involvement.
Scotland
Insulation inside a wall is often exempt from a warrant, but the exemption specifically excludes external wall cladding systems made of thermal insulating material. Applying EWI to a house is an alteration to the external wall, so a building warrant is normally required. Minor repairs to an existing system, like-for-like, are exempt.
Northern Ireland
Building control approval from your council is needed under the Building Regulations (Northern Ireland) 2012. Technical Booklet F covers energy and Technical Booklet E covers fire.
Related services
Questions people ask
Who arranges building control?
We arrange the notification or application as part of the job and give you the completion certificate for your records.
What if my wall can't reach 0.30?
Where thickness is limited, the regulations allow the best reasonable standard. The survey sets out what is achievable.