How access covers and gratings are measured
Access cover dimensions are always referred to by their ‘clear opening size’ and sometimes also by their frame depth.
The clear opening is the inside frame dimensions and these should normally be marked on the cover. If these are missing or have become illegible over time then it will be necessary to remove the cover and physically measure these dimensions.
The clear opening size of the access cover frame must always be equal to or greater than the size of the chamber it is covering to ensure the frame is adequately supported.
Clear opening size
Measure the dimension of the opening inside the brickwork or chamber. This will be the same size as the opening inside the frame we supply. Do not measure the size over the top of the existing frame or the frame size.
Let us know any restrictions you have for the size and depth of your frame. CD 534 states all trunk road and motorway ironwork should be 150mm deep, and many highway Authorities apply the same guidance for local roads.