A flitch beam is a steel plate sandwiched between pieces of lumber and through-bolted so they act together; a steel beam is a rolled W-shape. For a main beam or a long span in an Ontario house, a steel W-beam is usually the simpler choice: it's in the code's span tables, carries more load for its depth and needs no assembly. A flitch beam makes sense in specific renovation situations, such as building a beam in place from pieces that fit through a finished house, matching existing wood framing depth, or giving joists a wood surface to fasten to. Either way, a beam replacing a bearing wall needs a designer or engineer and normally a building permit.
What a flitch beam is
A flitch beam (or flitch plate beam) is built from three or more layers:
- Lumber plies, usually two dimension-lumber members or LVL
- One or more steel plates, most often a single plate in the middle, cut a little shallower than the wood
- Through-bolts at a designed spacing that clamp the layers so they bend together
The steel is much stiffer than the wood, so it takes a large share of the load; the wood braces the thin plate against buckling and provides surfaces to nail and screw into. The bolts are what make the two act as one beam, which is why their size, number and spacing are part of the design, not something to improvise. Our post on steel flitch plates and joist repair plates explains how load passes between plate and wood.
Span tables: steel has them, flitch beams don't
This is the main practical difference, and the reason searches for "flitch beam span tables" come up empty in Ontario.
Part 9 of the 2024 Ontario Building Code (O. Reg. 163/24) gives prescriptive spans for:
- Built-up wood and glued-laminated timber floor beams, in Span Tables 9.23.4.2.-H to 9.23.4.2.-K
- Steel beams, in Table 9.23.4.3. for floors in dwelling units and Span Tables 9.23.4.3.-A to -J for roofs and floors
There is no table for flitch beams. A flitch beam is always a designed member: an engineer works out the plate size, lumber, bolt pattern and bearing for the specific loads.
For comparison, here are a few values from OBC Table 9.23.4.3. (maximum spans for steel beams supporting floors in dwelling units). The supported joist length is half the sum of the joist spans on both sides of the beam.
| Section | 1 storey, 3.6 m joists | 1 storey, 4.8 m joists | 2 storeys, 3.6 m joists | 2 storeys, 4.8 m joists |
|---|---|---|---|---|
| W200x27 | 6.6 m | 6.1 m | 5.6 m | 4.9 m |
| W250x33 | 8.3 m | 7.7 m | 7.0 m | 6.1 m |
| W310x39 | 10.2 m | 9.5 m | 8.5 m | 7.4 m |
These spans apply only within the table's conditions: residential floor loads, steel meeting at least Grade 350W to CSA G40.21, and a top flange that counts as laterally supported under Sentence 9.23.4.3.(3), meaning wood joists bearing on the flange at no more than 600 mm, load delivered through the joists, and 19 mm by 38 mm wood strips nailed to the joists on both sides of the flange. Point loads, roof loads coming down through the beam, or anything unusual takes the beam out of the table. Our guide to steel beam span tables for Ontario homes covers how to read the full table.
Even when a steel beam fits the table, the posts, bearing and footings under it have to be right too, and the permit drawings still have to show it.
Flitch beam vs steel beam side by side
| Flitch beam | Steel W-beam | |
|---|---|---|
| What it is | Lumber plies bolted to a steel plate | One rolled steel section |
| Sizing | Always engineered | OBC Part 9 tables within limits, otherwise engineered |
| Capacity for its depth | Good, better than wood alone | Highest of the common options |
| Getting it into a house | Plies and plate carried in separately, assembled in place | Arrives as one piece, or spliced if the design allows |
| Heaviest single piece | The steel plate | The whole beam |
| Fastening joists and hangers | Directly to the wood faces | Needs a wood nailer or top plate, or steel connections |
| Assembly on site | Drilling and bolting through wood and plate | Set, shim and connect |
| Shrinkage | Lumber dries and shrinks; bolts may need retightening per the design | None |
| Matching existing framing | Easy to match a lumber depth | Depth set by the section; often dropped or packed out |
On weight, steel weighs about 7,850 kg per cubic metre. A 12 mm plate 280 mm deep and 4 m long is roughly 105 kg; a 4 m W250x33 is about 132 kg. Neither is light, but a flitch plate can sometimes be detailed in shorter spliced pieces if the engineer allows it, and the lumber plies go in one at a time.
When a flitch beam makes sense
- Renovations with no way to get a long beam in. Lumber plies and a plate can be carried through a finished house and assembled where the beam goes.
- Depth matched to existing wood framing. A flitch beam can be built to the same depth as the joists or an existing built-up beam.
- Joists and hangers fastening to wood. Framers can nail and screw to the wood faces as usual.
- Strengthening an existing wood beam. Adding a plate and bolts to a sagging or overloaded beam can be less disruptive than replacing it, where an engineer confirms it works.
- Openings in wood-frame walls where a header needs more capacity than lumber alone at the available depth.
When a steel beam makes sense
- Main beams in basements, especially replacing a wood beam and posts to open up the space. See replacing a wood basement beam with steel.
- Long spans and heavy loads, such as two storeys or a removed bearing wall with point loads above.
- Where the OBC table fits, which can simplify the design and permit process.
- Where headroom is tight, because a W-beam usually carries more load for its depth than wood or flitch options.
- Exterior and garage openings carrying masonry or floors. Exterior steel beams are required by Article 9.23.8.2 to be shop primed with rust-inhibitive paint.
If you're also weighing engineered wood, our comparison of steel beam vs LVL covers stiffness, span and depth. A "wood I-beam" in the sense of an engineered I-joist is a joist product, not a substitute for either beam.
What drives the cost of each
We don't publish prices, because the real number depends on the design and the site. What changes the cost:
- Flitch beam: engineering (always needed), plate size and finish, the number of bolt holes drilled in the shop, the lumber, and site labour to assemble, drill through the wood and bolt everything up.
- Steel beam: the section's weight and length, fabrication (cutting, holes, welded plates, priming), posts and base plates, and the effort to get it into the house and lifted into place. See what drives steel beam fabrication cost.
- Both: temporary shoring, footings under new posts, finishing work, and the permit.
Getting the steel for either option
Whichever beam your designer chooses, we can supply it. We cut and drill flitch plates to the engineer's detail, and we fabricate W-beams, HSS posts, base plates and cap plates, with priming or galvanizing to suit. We also supply and install basement beams and posts. If you don't have a design yet, engineering services are available for projects that need them. Send us your drawings or details, or see our steel products.
Frequently asked questions
Is there a span table for flitch beams in Ontario?
No. Part 9 of the 2024 Ontario Building Code has span tables for built-up wood and glulam beams and for steel W-beams, but none for flitch beams. A flitch beam's plate, bolts and lumber are sized by an engineer for each job.
Is a flitch beam stronger than a steel beam?
Usually not for the same depth. A rolled W-beam puts its steel in the flanges, where it does the most good in bending, while a flitch plate is a flat bar in the middle of the wood. Flitch beams are chosen for reasons other than maximum capacity, such as handling, nailing surfaces or matching existing framing.
When should you use a flitch beam?
Mostly in renovations: where a beam has to be assembled in place from pieces that fit through the house, where the beam must match the depth of existing wood framing, or where joists and hangers need to fasten directly to wood faces. An engineer still has to design it.
Is a wood I-beam the same as a flitch beam?
No. A wood I-beam usually means an engineered I-joist, a lightweight joist with wood flanges and a panel web. It is not a beam for carrying a bearing wall. A flitch beam is solid lumber bolted to a steel plate.
