8.18 Notching and Drilling Notching and Drilling of Joists Joists can be notched providing it is in accordance with reference in TRADA detail below:
Reference can be made to tables 2.17 and 2.18 which translates diagram 2.108 drilling and notching zones into actual dimensions for a number of typical depths and spans. •
Adjacent holes must not be closer than 3 times the diameter of the largest hole permitted.
•
A notch and a hole within the same joist must be at least 100mm apart measured horizontally along the centre of the joist.
•
Where the joist depth is greater than 250mm, then the dimensions of the shaded zones given in diagram 2.108 should be calculated using d = 250mm.
95
Depth of Joist *d* (mm)
Max. Depth of Notch 0.125d (mm)
Max. Diameter of Holes 0.25D (mm)
Min. Distance between Holes* (mm)
100
12.5
25
75
125
16
31
93
150
19
37.5
112.5
175
22
44
132
200
25
50
150
225
28
56
168
250
31
62.5
187.5
Notes: * distance given is when using maximum permissable hole size. If the joist depth is greater than 250mm, notch and hole sizes should not exceed those given for 250mm deep joist. If the joist depth is greater than 250mm, notch and hole sizes should not exceed those given for 250mm deep joists.