Llanelli:01554 778 730

Tech Update: Notches & Holes in Solid Timber Joists

How to get it right: Notches & holes in solid timber joists

 Floor Joists

When installing pipework or cabling, floor or ceiling joists may need to be notched or drilled. But this could weaken the floor to such an extent that it becomes structurally unsound.

To find out if this might be the case, guidance on notches and holes in solid timber joists for use in domestic properties can be found in section 3.22 of Eurocode 5 published by BM TRADA. 

The diagrams and tables below illustrate the zones and sizes permissible for differing spans and joist depths

Joists Diagram

  

Span of timber

Hole locations between

Notching locations between

mm

0.25 of span

0.4 of span

0.07 of span

0.25 of span

2000

500

8800

140

500

2500

625

1000

175

625

3000

750

1200

210

750

3500

875

1400

245

875

4000

1000

1600

280

1000

4500

1125

1800

315

1125

 

Depth of timber

Max hole diameter

Max notch depth

mm

0.25 x depth mm

0.125 x depth mm

100

25.0

12.5

125

31.3

15.6

150

37.5

18.8

175

43.8

21.9

200

50.0

25.0

225

56.3

28.1

250

62.5

31.3

275

65 (max)

34.4

300

65 (max)

35

 

Key points for notches and holes

Before you start work check that the joist size is adequate for the span.

Notches can only be made in the top OR bottom of the joists, (not both) within the permitted area to a maximum of 35mm.

Holes may only be made on the joist's centreline within the permitted area to a maximum diameter of 65mm.

Additional holes must be at least three diameters (centre to centre) apart.

Single/multiple timber structural beams, rafters, purlins and binders must never be notched or drilled without calculations to justify the remaining timber. Rafters may be birdsmouthed by no more than 1/3rd of the depth.

This guidance does not apply to engineered joists e.g. JJI joists and reference should be made to specific product manufacturers instructions.


Article produced by LABC

 

Llanelli:
01554 778 730
Cardiff:
02921 197 196