You can drill a steel beam, and fabricators do it on almost every beam they make, but any hole or notch that wasn't designed into it needs the engineer's approval. Bolt holes for connections are planned on the shop drawings and drilled or punched in the shop. Holes and notches added later, for a pipe, duct, cable or attachment, remove steel that the beam may be relying on. The usual tool for bolt-sized holes is a magnetic drill with an annular cutter; notches and copes are cut in the shop with rounded corners.
This post explains why location matters, what the common terms mean, and how to get holes and notches done the right way. It doesn't give step-by-step instructions for altering a beam in a house: that is a structural change, and it belongs with a designer or engineer and, often, a building permit.
Why a hole or notch is a structural question
A wide-flange beam works as a system. The flanges carry most of the bending, one in compression and one in tension. The web carries most of the shear and holds the flanges apart. Where the beam is working hardest depends on the load:
- Bending is usually highest near mid-span of a simply supported beam, so that is where flange material matters most.
- Shear is highest near the supports and under point loads, so that is where the web matters most.
- Concentrated loads and bearing points need the web to resist crippling and buckling, and may already have stiffeners.
A hole in the tension flange reduces the area resisting bending. A hole in the web near a support reduces shear capacity. A notch does both and also creates a stress concentration: a sharp internal corner where cracks can start under repeated load. Coping away a compression flange can also make the remaining section prone to local buckling.
None of that means a hole is always a problem. Many beams have reserve capacity, and engineers approve penetrations routinely. But only the engineer knows how close to its limit a particular beam is designed.
Holes, copes and notches: the terms
| Term | What it is | Typical purpose |
|---|---|---|
| Bolt hole | A drilled or punched hole sized for a bolt | Connections to columns, other beams, plates, wood nailers |
| Web penetration | A larger opening through the web | Pipes, ducts, conduit |
| Cope | A cut-out at the end of a beam, removing part of a flange and web | Lets a beam frame into another beam at the same level |
| Block | A rectangular cut-out removing flange and web at the end | Clearance at connections |
| Notch | Any cut into a flange or web along the length | Clearance for something passing the beam; needs design |
| Slot | An elongated hole | Adjustment in a connection, where the design allows it |
Some beams are made with openings on purpose. Castellated and cellular beams have regular web openings designed in from the start, so services can pass through. If a project needs lots of web penetrations, raise it early, before the beam is chosen.
Where holes usually do least harm
As general guidance, which your engineer will confirm or override for the actual beam:
- In the web, near mid-depth, where bending stresses are lowest.
- Away from supports and point loads, where shear and bearing stresses are highest.
- Well clear of the flanges and the fillet where web meets flange.
- Spaced apart from other holes, so they don't combine into one weak zone.
- Round rather than square, or with generously rounded corners.
Holes through the flanges, especially the bottom flange of a simply supported beam, are the ones to avoid unless they are designed in. If a hole is unavoidable in a highly stressed area, the engineer may call for a reinforcing plate or stiffeners around it.
Hole sizes for bolts
The answer to "what size hole for an I-beam" depends on the bolt. Standard bolt holes are slightly larger than the bolt diameter, by an amount set in CSA S16, the Canadian steel design standard. Oversized and slotted holes change how the connection carries load and are only used where the design allows them. Your shop drawings will show each hole's size and location, and the bolt type and diameter.
A few practical points:
- Drill or punch bolt holes; don't burn them. A torch-cut hole is rough and out of round, and the bolt won't bear evenly.
- Don't enlarge holes in the field to make parts fit. A misaligned hole is a fit-up problem for the fabricator and engineer to resolve, not something to fix with a bigger bit.
- Lag screws and bolts for wood nailers follow their own spacing and edge distance rules. See attaching a wood top plate to a steel beam.
Drilling steel beams: tools and practice
For anyone planning work on a beam, here is what the job involves so you know what to expect from the trade doing it:
- Magnetic drill with annular cutters. The standard tool for bolt holes in flanges and webs. The magnetic base holds the drill to the steel, and the annular cutter removes a ring of material rather than the whole hole, so it cuts faster and cooler than a twist bit.
- Cobalt (HSS-Co) twist bits. For small holes, such as pilot holes or fasteners for light attachments. Step bits only suit thin material.
- Cutting fluid and low speed. Structural steel is tough; running a bit too fast overheats and dulls it.
- Secure the drill. A magnetic base needs clean, flat, bare steel to hold, and a safety strap or chain when drilling on a vertical face or overhead.
- Mind the swarf. Chips are hot and razor sharp.
In an occupied house, there are extra checks: temporary support if the beam is loaded and the work is significant, fire protection or coatings that may need to be restored, and whatever services are already near the beam. Our post on whether steel beams in houses need fireproofing covers the fire side.
Notching and coping
Coping in the shop is routine. When a beam frames into another beam with tops level, its top flange and part of its web are cut away at the end so it fits under the other beam's flange. Fabricators cut copes with saws, coping equipment or thermal cutting, then form a rounded corner at the inside of the cut instead of a sharp one and grind the edges, because a sharp re-entrant corner is where cracks start. The engineer checks the coped section for the load it carries.
Notching an installed beam is different. It is common in renovations, for a duct or a lowered ceiling, and it is a structural alteration every time. Expect the engineer to look at:
- How much flange and web will be removed, and where along the span.
- Whether the remaining section can carry the bending and shear.
- Whether a reinforcing plate, stiffeners or a different detail is needed.
- How the cut will be made and finished.
Often the answer is to reroute the service or use a different beam detail. Our post on whether you can cut or weld an existing steel beam covers shortening, splicing and welding to beams in place.
Get holes and copes on the shop drawings
The cheapest and safest hole is one drilled in the shop before the beam is delivered. That means collecting the penetrations early:
- Ask the mechanical and electrical trades where they need to pass through or attach to steel.
- Get the engineer to approve the sizes and locations.
- Put them on the shop drawings, so every hole is dimensioned and drilled with the connection holes.
We fabricate beams with plates, holes and connections ready for install, and prepare shop drawings in-house. Engineering services are available for projects that need them. For more on what happens to a beam in the shop, see how a steel beam is fabricated.
Send us your drawings for a free take-off and quote, or see our steel products.
Frequently asked questions
Can you drill holes in a steel beam?
Yes, and fabricators do it on every beam for bolted connections. Extra holes added later, for pipes, wiring or attachments, remove steel the beam may need, so the location and size should be approved by the engineer who designed it.
Where is it safest to drill a hole in a steel I-beam?
In general, holes do least harm in the web near mid-depth, away from supports, point loads and other holes. Holes in the flanges, especially the tension flange, cut into the part of the beam that resists bending. The engineer decides what is acceptable for a particular beam.
What drill bit do you use for a steel beam?
For bolt-sized holes, a magnetic drill with an annular (core) cutter is the standard tool. Small holes can be drilled with cobalt twist bits. Use cutting fluid, keep speeds low and clamp or strap the drill securely.
Can you notch a steel beam?
Beam ends are routinely coped in the shop so one beam can frame into another. Notching an installed beam is a structural change that needs an engineer, because a notch removes steel and creates a sharp corner where cracks can start.
