You can extend a detached dwelling by 8m to the rear if it’s a detached house or 6m if it’s semi-detached or terraced. There are height restrictions but they boil down to a single storey extension not being higher than 4m in height to the ridge and 3m to the eaves, and ridge heights of any extension not being higher than the existing property.
Two storey extensions must not be closer than 7m to the rear boundary.It must be built in the same or similar material to the existing dwelling.Extensions must not go forward of the building line of the original dwelling.
Side extensions must be single storey, maximum height of 4m and a width no more than half of the original building.
In designated areas side extensions require planning permission and all rear extensions must be a single storey.
An extension must not result in more than half the garden being covered.