Step 1 – Decide on Grating Width (A)

 

Step 2 – Decide on Grating Height (B) (Determined by Strength Requirement)

 

Step 3 – (C) is determined by (B)

 

Step 4 – To determine (D), add 20mm to (C) (To allow for movement)

 

Step 5 -  To determine (E), the actual trench width, Use (D) and subtract the frame size twice .

 

For example. The trench cover is 300mm(A) wide and 25mm(B) high. The Frame is thus 30mm(C). The Frame Width(D) then needs to be A + 20, which is 320. The actual trench width needs to be 320 – 30 – 30 = 260mm.

 

If the trench is already dug, work in reverse and add the frame size to the trench width twice.