Installing a steel beam in a basement follows a set sequence: an engineer designs the beam, posts and footings, a permit is issued, the beam is fabricated to field measurements, footings are poured, the floor above is shored, the old wall or beam comes out, the new beam is lifted onto its bearings, the joists are connected, and the work is inspected before the shoring comes out. Most of the time goes into the preparation; setting the beam is a small part of the job.
This post explains each stage so you know what to expect, what to ask and who does what. It's not a set of DIY instructions. Installing a beam under a loaded floor is structural work that needs approved drawings, a permit in almost every case, and a qualified crew. For what drives the price, see cost to install a steel beam in a basement.
Why basement steel beams get installed
Most basement beam jobs fall into one of these:
- Removing a basement load-bearing wall to open up the space. The wall is replaced by a beam and a few posts.
- Replacing a sagging or undersized wood girder. Covered in detail in replacing a wood basement beam with steel.
- Fewer posts. A steel beam spans farther than a built-up wood beam of the same depth, so posts can come out.
- Headroom. Steel carries the same load at a shallower depth, or can be set flush with the joists.
- New loads from above, such as a main-floor wall removal that sends point loads down into the basement.
Design decisions before steel is ordered
The engineer or designer settles these before anything is fabricated:
Beam size and grade. For a simple beam carrying floor loads in a house, Table 9.23.4.3 of the 2024 OBC gives maximum spans for common W-shapes based on the supported joist length, and Sentence 9.23.4.3.(2) requires those beams to be at least Grade 350W. Most real jobs, especially with point loads or removed walls, are engineered. The tables don't cover point loads, so treat them as a check, not a design.
Drop or flush. A drop beam sits below the joists, which keep bearing on top. A flush beam sits up in the joist depth so the ceiling stays flat, and the joists are cut and supported on the beam.
Bearings at each end. Usually a pocket in the foundation wall or a steel post. Article 9.23.8.1 requires even, level bearing at least 89 mm long at end supports. See steel beam bearing length on concrete and masonry.
Posts and footings. Where the beam needs intermediate supports, each post gets its own footing, centred under it.
Lateral support. The span tables assume a laterally supported top flange. Sentence 9.23.4.3.(3) treats a beam as laterally supported when wood joists bear on the top flange at no more than 600 mm along its length, the load comes through the joists, and 19 mm x 38 mm wood strips touching the top flange are nailed to the bottom of the joists on both sides. Flush beams and beams with point loads need the engineer to address lateral support directly.
The installation sequence on site
1. Field measurements and fabrication
The beam length, post heights and bearing elevations are measured on site, ideally after demolition opens things up. The beam is then cut to length and fabricated with whatever the drawings call for: bearing plates, holes for bolts or a wood nailer, connection plates for posts, and a splice if the beam is too long to get into the basement in one piece.
2. Footings and posts
Slab is cut at each new post location, footings are excavated and inspected if required, and concrete is poured and allowed to cure. Pockets are cut or prepared in the foundation wall for the beam ends.
3. Shoring
Temporary walls or adjustable shores go in on one or both sides of the beam line to carry the floor while the old wall or beam is removed. Shoring holds the floor where it is. It isn't used to jack a sagging floor back up unless the engineer has planned that.
4. Removing the old wall or beam
With the shoring carrying the load, the old structure comes out. Services in the way (ducts, plumbing, wiring) are moved by the relevant trades before or at this stage.
5. Getting the beam in and up
The beam is carried or rolled in through the widest route available: a walkout, a basement window opening or the stairs. It is then raised onto its bearings with a material lift, jacks and cribbing, or a crew with straps. Our guide on lifting a steel beam into a house without a crane covers the methods and safety.
6. Setting and fastening the beam
The beam is set on its bearings, levelled, and the posts are installed underneath and fastened top and bottom. Any gap between the beam and the floor above is packed solid as detailed, so the floor bears evenly.
7. Connecting the joists
How the joists connect depends on the beam position:
| Joists on top (drop beam) | Joists framed in (flush beam) | |
|---|---|---|
| Joist support | Bear on the top flange | Bottom flange, or 38 x 38 mm lumber bolted to the web with bolts at least 6.3 mm diameter, spaced no more than 600 mm |
| Over the beam | Nailer or wood strips per the drawings | 38 x 38 mm splice at least 600 mm long joining the joists above the beam |
| Shrinkage | Less of an issue | At least 12 mm gap between the splice and the beam |
| Headroom | Beam hangs below ceiling | Flat ceiling |
The flush-beam rules come from Article 9.23.9.2 of the 2024 OBC. The 12 mm gap matters: wood joists shrink as they dry, and without it the floor can end up sitting on the steel and humping over the beam line. Many installers attach a wood nailer to the top flange to give the subfloor or joists something to fasten to.
8. Inspection and shoring removal
The building inspector sees the beam, posts, bearings and connections before anything is covered. Once the work is approved and the posts are carrying the load, the shoring is removed and finishing can start.
Removing a load-bearing wall in the basement
A load-bearing wall in a basement usually sits under the main-floor joists, often on its own strip footing. Replacing it with a beam changes how the load reaches the ground: instead of a continuous wall spreading load along a footing, the beam collects it and delivers it as point loads at the posts and ends. That is why:
- the posts usually need new pad footings, even if the old wall had a footing
- the beam ends need proper bearing in the foundation wall or on posts
- the engineer checks whether any walls or posts above land on the new beam
Removing a main-floor or upper-floor wall follows a similar logic, with the added step of carrying the load down through every floor. See how to remove a load-bearing wall and install a beam.
Who does what
| Role | Responsibility |
|---|---|
| Engineer or qualified designer | Sizes the beam, posts, footings and connections; prepares drawings |
| Building department | Reviews drawings, issues the permit, inspects |
| Fabricator | Cuts, drills and welds the beam and posts to the drawings and field measurements |
| Contractor or installer | Shoring, demolition, footings, setting the beam and posts, joist connections |
| Other trades | Moving ducts, plumbing and wiring; finishing |
You can split these between companies or have fewer of them do more. What matters is that someone is clearly responsible for each line.
Getting your basement beam supplied or installed
We supply, fabricate and install structural steel for homes, including basement beams and posts, with shop drawings in-house and engineering services available for projects that need them. Send us your engineer's drawings or your measurements and photos for a free quote on the steel, supplied or supplied and installed, and see our services for how a job runs from drawings to installation.
Frequently asked questions
Do you need a permit to put a steel beam in a basement?
In almost every case, yes. Ontario's Building Code Act requires a permit to construct, which includes material alteration of a building, and a new beam with new posts and footings is a structural alteration. Your municipal building department will confirm what drawings it needs.
How does a steel beam sit on a foundation wall?
Usually in a pocket formed or cut into the concrete wall, on a level bearing surface. Article 9.23.8.1 of the 2024 OBC requires beams to have even and level bearing at least 89 mm long at end supports, and the engineer may require more, a bearing plate, or a post instead of a pocket.
Can floor joists sit flush with a steel beam?
Yes. Under Article 9.23.9.2, joists framed into the side of a steel beam are supported on the bottom flange or on 38 mm by 38 mm lumber bolted to the web, and spliced over the top with a gap left above the beam for shrinkage. A flush beam saves headroom but takes more labour.
Can I install a steel beam in my basement myself?
It isn't a DIY job. The floor above has to be shored, footings poured, a heavy beam lifted onto its bearings and the joists reconnected, all to approved drawings and inspections. Homeowners can hire the trades and manage the project, but the structural work belongs with a qualified crew.
