Can I Drill a Hole in the Beam Web?

Drilling holes through a steel beam web for bolts, services or other fixings is sometimes necessary on site. Small holes for standard connections are generally acceptable, but larger or poorly positioned holes can seriously weaken the beam. There are clear rules on when you can proceed without further calculations — and when you cannot.

Standard Bolt Holes: Always Acceptable

Holes for M12 to M20 bolts (standard connection hardware) are acceptable in all beam webs provided they are spaced in accordance with the spacing requirements in BS EN 1993-1-8. These are fabrication-standard holes and do not require separate engineering approval.

Larger Holes Without Calculations: Strict Criteria

For holes larger than standard bolt holes — for example, a 50 mm hole for a waste pipe — the following criteria all apply:

1. Middle third of depth — the hole centre must be within the middle third of the beam’s overall depth (i.e. between d/3 and 2d/3 from each flange)
2. Middle third of span — the hole must be within the middle third of the beam’s span length (i.e. between L/3 and 2L/3 from each support)
3. Centre-to-centre spacing — if there are multiple holes, their centre-to-centre spacing must be at least 2.5 × the diameter of the larger hole
4. Distance from flange — the hole centreline must be at least one full beam depth away from any point load or reaction location
5. No heavy point loads — the beam must not carry heavy concentrated loads (e.g. columns or multi-storey loads bearing onto it)
6. Not a narrow section — sections with very narrow webs (e.g. 152×52×23 UB) may not accommodate these rules — check the web thickness is sufficient

If all of the above criteria are met, a single circular hole without stiffening is generally acceptable without separate engineering review.

When Calculations Are Required

Any of the following situations require calculations and may incur an additional fee:

– The hole falls outside the middle-third zones
– Multiple holes are closer than the 2.5× spacing rule
– The beam carries heavy point loads
– The hole is non-circular
– The beam is a very shallow or narrow section

Before You Drill

Check the position against all five criteria above. If there is any doubt, contact PorthouseDean before drilling — a hole in the wrong position cannot be undone without welded repair, which requires structural assessment.

Contact us if you are unsure whether your planned hole position meets these requirements.