Just thought I would test your little grey cells with a conundrum that has always puzzled me.
The above rule only allows you to take the floor area of the extension. However often the extension totally encloses an "inner" room and the separating wall is removed to make one large space.
So for example you have a 10m² extension on a 15m² room. The rules only allow 2.5m² (25% of 10m²) of windows plus any existing windows so lets say another 2.0m² giving us 4.5m² in total.
With the current trend for these huge sliding folding doors and rooflights the window area nearly always exceeds the 25% of the extension. If you took the room as a whole, 25m², then 25% of the total floor area would allow a total window area of 6.25m². If you have a small extension on a large room the anomaly is even worse. So the 25% rule contradicts the 20% rule for minimum window area. I usually get round it with an area weighted calculation but it always bothered me that the client has the extra expense of added insulation and thicker walls etc. for no good reason.
Has anyone ever come across a scenario where Building Control has allowed you to take the floor area of the entire room not just the extension? That strikes me as the logical way to calculate the maximum window area.
The above rule only allows you to take the floor area of the extension. However often the extension totally encloses an "inner" room and the separating wall is removed to make one large space.
So for example you have a 10m² extension on a 15m² room. The rules only allow 2.5m² (25% of 10m²) of windows plus any existing windows so lets say another 2.0m² giving us 4.5m² in total.
With the current trend for these huge sliding folding doors and rooflights the window area nearly always exceeds the 25% of the extension. If you took the room as a whole, 25m², then 25% of the total floor area would allow a total window area of 6.25m². If you have a small extension on a large room the anomaly is even worse. So the 25% rule contradicts the 20% rule for minimum window area. I usually get round it with an area weighted calculation but it always bothered me that the client has the extra expense of added insulation and thicker walls etc. for no good reason.
Has anyone ever come across a scenario where Building Control has allowed you to take the floor area of the entire room not just the extension? That strikes me as the logical way to calculate the maximum window area.