Building Regulations and Planning Permissions

What Are The Differences Between Welsh Building Regulations And English Building Regulations?

Are there any changes between the key approved documents?

Building regulations are ever-changing and sometimes difficult to keep up to date with.


The most important documents that concern glazing systems are Document O, Document L and Document F. The frequent questions we receive at IQ are what are these documents? And are there differences between Welsh building regulations and British building regulations?

 Double casement windows in bedroom of New House Cornwall

Document O

Approved Document O contains the details regarding overheating in buildings. Solar gain and overheating due to poor glazing can cause a few issues especially in smaller dwellings and more intimate spaces such as a living room. Document O ensures that overheating is kept to an absolute minimum, especially for new builds.  

The Welsh building regulations are very similar to the English ones when comparing the simplified sections. The Welsh document O tends to be slightly more relaxed. For IQ Glass the scope of our work lies more towards the Dynamic section of document O which contains very little differences.  

The main difference is that in the Welsh Document O, requirement 01 states that the Overheating mitigation applies only to the erection of dwellings and institutions such as a school. On the other hand, the same rule stands for every type of building that is erected in England, there are no exceptions.  

Glovers Barn Grade II listed sustainable dwelling with IQ Glass

Document L

Approved Document L focuses on the conservation of fuel and power. Energy efficiency is key for dwellings, especially ones with large glazing features such as slim sliding doors. Document L features one key difference between the Welsh and English versions.  

In England homes must now produce 31% less carbon into the atmosphere. On the other hand, the Welsh building regulations state that now dwellings must produce 37% less carbon. While 6% seems insignificant it may lead to redesigning of glazing systems or the placement of said systems.  

Glass wall living room facade to modern riverside dwelling.

Document F

Ventilation is the priority of Document F. Document F says that adequate ventilation needs to be provided to prevent excess condensation build up which could damage the structure of a property. Document F in both England and Wales follow very similar direction with very minimal changes between the two.  

The key statement in Document F is “There shall be adequate means of ventilation provided for people in the building”. This is the same in both documents and excludes rooms used for storage and garages connected to a dwelling. This applies to both England and Wales. 


If you have any questions regarding these approved documents, or have any questions regarding our glazing systems, do not hesitate to contact the team here.