Page 135 - The City and Guilds Textbook: Plumbing Book 1 for the Level 3 Apprenticeship (9189), Level 2 Technical Certificate (8202) and Level 2 Diploma (6035)

Chapter 2 Common processes and techniques

Span × 0.4

Span ×
0.25

D
Centre Span
line

1.25 ×
depth
At least
3 × D

Holes must be at least 3 diameters (centre to centre)
apart and no holes must be within 100 mm of a notch

p Figure 2.42 The positioning of holes drilled in joists

IMPROVE YOUR MATHS ACTIVITY
Again, to understand this fully we must look at the calculation. Let us take the The span of a joist
above joist measurement once more: measures 4.5 m long
and 200 mm in depth.
Length of span of the joist = 4 m
Using the calculations
25% of the span = 4 × 0.25 = 1 m shown above as a guide,
calculate:
40% of the span = 4 × 0.4 = 1.6 m
a the area where holes
Therefore, holes drilled or cut in the joist must start 1 m from the end of the joist can be made
and must finish 1.6 m from the end of the joist. All holes required must be made
within a distance of 600 mm. Again, this can be done from both ends of the b the maximum size of
joist, so two sets of holes can be made. those holes.
To calculate the size of the holes:
KEY TERM
Depth of the joist = 250 mm

25% of the depth = 250 × 0.25 = 62.5 mm Centre to centre: measuring
from the centre line of one
This measurement must be measured equally either side of the centre line of the pipe to the centre line of
joist. No holes can be drilled in a joist within 100 mm of a notch and circular another, so that all the tube
holes must be at least three diameters of the hole size apart measured centre centres are uniform. This
to centre.
ensures that the pipework
will look perfectly parallel
Cutting chases in walls because all of the tubes will
be at equal distance from
Occasionally, it may be necessary to cut a chase in a wall to conceal pipework; one another.
for example, burying pipes for a downstairs radiator. This will involve the use
of an angle grinder to, first, cut the outline of the chase onto the wall and then
carefully removing the unwanted masonry from between the cuts. Caution
should be exercised.
Chases cut in walls must be cut to no more than the following depths:

● horizontal chases must not be deeper than one-sixth of the wall thickness
● vertical chases must not be deeper than one-third of the wall thickness.

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