Joists can be hung from a steel beam, but hangers aren't nailed to the steel. They are fixed to wood bolted to the beam, such as a filler in the web or a nailer on the top flange, or the fabricator welds steel seats to the beam, or the joists simply sit on the bottom flange. In Ontario, Sentence 9.23.9.2.(3) of the 2024 Building Code gives the basic rule for joists framed into the side of a steel beam: they must bear on the bottom flange or on at least 38 x 38 mm lumber bolted to the web. Whatever hanger you use, its rating depends on what it's fastened to, so the detail belongs on the drawings.
Hanging joists off the side of a beam, rather than setting them on top, is how a steel beam ends up flush with the ceiling. It's common when removing a loadbearing wall upstairs or keeping headroom in a basement.
Dropped or flush: two ways to frame joists to steel
Article 9.23.9.2 permits floor joists to be supported on the top of a beam or framed into its sides.
| Dropped beam | Flush beam | |
|---|---|---|
| Where the beam sits | Below the joists | Within the joist depth |
| How joists connect | Bear on a wood nailer on the top flange | Bear on the bottom flange, a ledger, hangers or seats |
| Ceiling | Beam shows below the ceiling, boxed or exposed | Flat ceiling |
| Complexity | Simpler | More connection work, often engineered |
A dropped beam with a nailer is the simplest detail and is covered in attaching a wood top plate to a steel beam. The rest of this post is about the flush case, where joist hangers come in.
What the Ontario code requires for flush framing
Sentence 9.23.9.2.(3) of the 2024 OBC says that when joists are framed into the side of a steel beam, they must be supported on:
- the bottom flange of the beam, or
- at least 38 mm by 38 mm lumber bolted to the web, with bolts at least 6.3 mm in diameter spaced not more than 600 mm apart.
Sentences (4) and (5) add that the joists must be spliced above the beam with at least 38 x 38 mm lumber, at least 600 mm long, to support the flooring, with at least a 12 mm space between that splice and the top of the beam to allow for the wood joists to shrink.
That last point matters more than it looks. Wood joists shrink as they dry, but the steel doesn't. If the subfloor bears on the beam's top flange while the joists on either side shrink, the floor develops a hump along the beam line. The gap prevents it.
For wood beams, Sentence 9.23.9.2.(2) mentions joist hangers specifically. The steel beam sentence doesn't, so hangers on a steel beam are an alternative to the basic detail, and the designer should show which hanger, what it's fastened to and how.
Hanger options for steel beams
Joists on the bottom flange
The simplest flush detail. Joists are notched at the bottom end to sit on the bottom flange, or cut so their ends bear on it directly. It needs a beam whose depth suits the joists, and the joist notch has to stay within what the designer allows. Bearing on narrow flanges is limited, and Article 9.23.9.1 requires at least 38 mm of end bearing for floor joists.
Bolted ledger on the web
A 38 x 38 mm or larger ledger is bolted to each side of the web, and the joists sit on it, matching the code detail above. Holes for the bolts are best drilled in the shop to the drawing so the spacing is right and the web isn't weakened by random site drilling.
Wood filler in the web with face-mount hangers
Wood blocking is bolted into the space between the flanges on each side of the web, filling it out to give a flat wood face. Standard face-mount joist hangers are then nailed into the filler. The hanger's published capacity assumes a wood header of a certain size and species, so the filler has to be sized and bolted to suit, and the bolts have to carry the joist loads into the web.
Top-flange hangers
Top-flange hangers hook over the top of the supporting member. On a steel beam they usually hook over a wood nailer bolted to the top flange, so the joist hangs below. Some manufacturers make hangers intended for steel, fastened with welds or powder-actuated pins. Use only products rated for that use and install them exactly as the manufacturer specifies.
Welded steel seats and angles
For heavier joists, engineered joists or tight details, the fabricator can weld steel angles or bent plate seats to the beam web. The joists bear on the seats and are fastened through pre-drilled holes. Welded seats are made in the shop under CWB certified welding, which is much more reliable than field welding inside a house.
| Option | Strengths | Watch for |
|---|---|---|
| Bottom flange bearing | No hardware; matches code | Beam depth must suit joists; notching limits |
| Bolted ledger | Matches code; simple | Ledger and bolt spacing on drawing |
| Wood filler and face-mount hangers | Standard hangers, flat ceiling | Hanger rating depends on filler and bolts |
| Top-flange hangers | Fast installation | Rated products only; nailer or steel fastening |
| Welded seats | Strong, precise | Must be detailed before fabrication |
Matching beam depth to joist depth
A flush beam has to fit within the floor depth. Dressed 2x10 joists are 235 mm deep and 2x12s are 286 mm. A W200x27, about 207 mm deep, sits within a 2x10 floor with room for the 12 mm shrinkage gap above, while a W250 group beam, about 247 to 266 mm deep depending on weight, suits a 2x12 floor. Engineered I-joists come in other depths again.
Shallower, heavier sections often work for flush beams because the depth is limited. The Canadian W-shape size chart lists actual depths, which vary within each nominal group. Your designer picks the section, and the flush beam option in our wall removal alternatives post explains the trade-offs.
Lateral support changes with flush framing
Part 9 steel beam span tables assume a laterally supported top flange, typically achieved by joists bearing on the top flange. When joists frame into the sides, that support comes from the joist connections and the subfloor instead, and whether it's enough is a design question. That's one reason flush steel beams are usually engineered. See our steel beam span tables guide for the conditions behind the tables.
Beam-to-beam and other hanger questions
"Steel beam hanger" also refers to a steel beam framing into another steel beam, which is a steel connection with shear tabs, clip angles or seats. That's a separate topic covered in steel beam-to-beam connection details.
For a joist repair rather than a new connection, see steel flitch plates for joist repair.
Ordering a beam ready for hangers
Most of the work in a flush beam detail can be done in the shop:
- Bolt holes in the web for ledgers or fillers, at the spacing on the drawing
- Holes in the top flange for nailers or hanger fastening
- Welded seats or angles for joists
- Cap and base plate connections for the posts
We fabricate steel beams with holes, plates and welded seats to your drawings under CWB certified welding, and we supply and install basement beams and posts. Engineering services are available for projects that need them. Send us your drawings for a free quote, and see our steel products for beams, plates and posts.
Frequently asked questions
Can you use joist hangers on a steel beam?
Yes, but not by nailing them to the steel. Hangers are fixed to wood bolted to the beam (a filler in the web or a nailer on the top flange), or special hangers rated for steel are used, or the fabricator welds steel seats to the beam. The connection and its rating should be shown by the designer.
What does the Ontario Building Code say about joists framed into a steel beam?
Sentence 9.23.9.2.(3) of the 2024 OBC says joists framed into the side of a steel beam must sit on the bottom flange or on at least 38 mm by 38 mm lumber bolted to the web with bolts of at least 6.3 mm diameter at no more than 600 mm. The joists are spliced over the beam with 38 x 38 lumber at least 600 mm long, with a 12 mm gap above the beam for shrinkage.
How do you attach floor joists to an I-beam?
Either the joists bear on top of the beam, usually on a wood nailer bolted to the top flange, or they are framed into its sides so the beam is flush with the ceiling. Flush framing uses the bottom flange, a bolted ledger, hangers on wood fillers, or welded seats.
Do steel beam hangers need an engineer?
Joist connections that follow the Part 9 rules for a house can be detailed by a designer, but hangers on steel rely on manufacturer ratings and on how the wood is fastened to the beam. Flush steel beams also change the beam's lateral support, so they are usually engineered.
