Hep20 Technical Handbook

Parameters for Drilling
Through Traditional Joists
The Building Regulations 1992
Approved Document A gives
exact instructions on the drilling
of floor joists.
The requirements of the
regulations are detailed below:
•
hole diameters should be no
greater than 0.25 of the depth
of the joist and should be
drilled at the neutral axis.
•
they should be not less than 3
diameters (centre to centre)
apart and should be located
between 0.25 and 0.4 times
the span from the support.
and illustrated in Figure 16.
The value 0.25 is obviously one
quarter and can easily be
calculated on site. The value 0.4
is less obvious and can be
obtained from the graph
(Figure 17).
Reading in conjunction with
Figure 16, the following example
illustrates the use of the graph:
Joist span is 4.5m.
Find value on horizontal scale
and read-up to sloping line.
Transfer point of intersection to
the vertical scale and read 1.8m.
0.25 x L
0.4 x L
Figure 16
Drilling requirements for traditional joists
Figure 17
Joist drilling zone from support
Span (L)
Not less than 3 diameters apart
centre to centre
Distance from support (m)
2.0
1.5
1.0
0.5
Holes should be located in this
zone and drilled at the neutral axis
Maximum diameter of a hole
0.25 x D
Maximum distance from support
Depth of joist (D)
Neutral axis of joist
Minimum distance from support
1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
Span of joist (m)
Parameters for Drilling
Through Engineered Joists
Hep 2 O ® is ideal in buildings
incorporating timber ‘I’ joists.
Piping can be properly installed
through holes in the web section
without damaging flange
members (e.g.TJI Joist system,
Trus Joist MacMillan Ltd.) even
where the pre-formed holes do
not align on the plan.
Refer to Figure 18.
Flange
Flange
Not less than 3 diameters apart
centre to centre
Web
Additional holes can be cut
but leave minimum 3mm of
web at top and bottom
38mm diameter knockouts
are incorporated in TJI joists
at approx 300mm centres
Figure 18
Drilling requirements for engineered joists
65