One of the most hotly debated topics when it comes to traditional conservatories is in the form of a building regulation that is no longer in government guidelines yet is still commonly enforced.
Some people looking into building a conservatory may have heard of the 75 per cent rule, and the 50 per cent rule that goes along with it, and there is a belief that a conservatory has to follow these strict guidelines in order to qualify as a conservatory.
In practice, this is far from the case as many conservatories and orangeries have solid roofs, and it can be somewhat confusing to understand what is allowed and whether a solid roof conservatory would need planning permission.
The problem is multiple interpretations of building regulations, and a conflation between these, permitted development rights for conservatories and local planning authority requirements.
As the 75 per cent rule if not mitigated with suitable UV shielding glass can cause the room to feel exceptionally hot in summer and cold in winter, it is important to know where you stand.
What The Building Regulations Say
Despite common misconceptions, the Approved Documents that form the Building Regulations do not, in fact, state the rule that a conservatory roof must consist of 75 per cent “glazed material” nor that the extension walls must have 50 per cent of their space be covered by windows.
This used to be in the building regulations prior to 2010, but after that, this particular piece of guidance was removed, with the only rule concerning conservatories and glazing being that the glass used had to follow Approved Document K’s rules on being visible enough to avoid injury.
Similarly, the Planning Portal’s guidance states that the rules for a conservatory are the same as any other extension.
To be exempt from building regulations, the conservatory needs to have a floor area of less than 30 square metres, be “thermally separated” (i.e. use its own heating system) through the use of thermally efficient windows, walls and doors, and have its own independent heating system.
However, because the final decision rests with the local planning authority, it is always essential to check, as some planning authorities still enforce the 75 per cent rule as a way to differentiate conservatories from other forms of extension.
This is also the case if you have an existing conservatory and plan to change the roof to help improve the insulation in winter and heat resistance in summer, and as with all major projects, checking with your local planning authority now stops expensive issues from forming in the future.
If the local planning authority decides that the solid conservatory roof must comply with building control regulations, there are typically two approaches that can be taken.
The first is the more conventional route of an inspector seeing the work and approving it for use once completed, whilst the other is through the use of a system that is already approved for use and only requires an inspection after installation so it can be confirmed that it has been appropriately installed.