A lally column needs a steel plate at each end: a cap (top) plate where it meets the beam and a base plate where it bears on the footing. Under the 2024 Ontario Building Code, each plate must be at least 100 mm × 100 mm × 6.35 mm (about 4 in × 4 in × 1/4 in), and under a wood beam the top plate must run the full width of the beam. The plates spread the column's load, give something to fasten through, and keep the column from shifting sideways.
The plates look like minor details, but they're where many basement column problems start: loose tops held with shims, plates narrower than the beam, and bases rusting in a damp slab.
What the plates do
A column concentrates a lot of load onto a small circle of steel. The plates deal with what happens at each end:
- Spread the load. A bare tube end would dig into a wood beam or a concrete footing. A plate distributes the load over a larger area.
- Provide a fastening point. The code requires columns to be securely fastened to the member they support to prevent lateral movement (Sentence 9.17.2.2.(1)). The top plate is how that happens.
- Give a square, flat bearing. The plate makes sure the column bears evenly rather than on one edge of a cut tube.
The Ontario code minimums
Article 9.17.3.2. of the 2024 Ontario Building Code sets out the plate requirements for steel columns in houses:
| Rule | Requirement |
|---|---|
| Plate size at each end | At least 100 mm × 100 mm × 6.35 mm thick |
| Top plate under a wood beam | Must extend across the full width of the beam |
| Top plate under a steel beam | May be omitted where the column is attached to the beam another way |
These are minimums for columns within the scope of Part 9. Engineered posts often have larger and thicker plates, with specific hole sizes and positions shown on the drawings.
Check plates on imported columns
Many columns sold under the lally name are made for the US market and US codes. Plate thickness varies by product: one major US manufacturer, for example, lists a standard end plate of 0.205 in (about 5.2 mm), which is thinner than Ontario's 6.35 mm minimum. Plate width also matters, since a plate that is narrower than a built-up wood beam doesn't meet the full-width rule. If you're buying a column off the shelf for an Ontario house, check the plates against the numbers above, or ask your designer.
Cap plates for wood beams
Most older Ontario basements have a built-up wood beam, sometimes on teleposts. The top plate under a wood beam needs to:
- Span the full width of the beam. A three-ply beam of 38 mm lumber is about 114 mm wide, which is already wider than the 100 mm minimum plate. The plate has to be sized to the actual beam.
- Be fastened up into the beam. Typically through pre-drilled holes in the plate. The type, size and number of fasteners should come from the designer or the column maker's instructions.
- Sit tight to the beam. Gaps filled with stacked shims or wood blocks mean the load isn't bearing evenly, and the column can work loose.
Some columns use a U-shaped saddle or plate with side tabs that wrap the sides of the beam. These help hold the beam in place and give extra fastening points into the sides of the plies.
The load from the column bears on the wood across the grain, and wood is relatively soft in that direction. On heavily loaded beams, the designer may call for a larger plate or a specific bearing detail so the beam doesn't crush. Our guide to connecting a steel post to a wood beam covers the connection options in more detail.
Cap plates for steel beams
Under a steel W-beam, the code allows the top plate to be left off where there's another way of attaching the column to the beam. In practice, columns under steel beams usually still get a cap plate, because it gives a clean way to connect:
- Bolted: the cap plate and the beam's bottom flange are drilled to match and bolted together. This is common on renovations because it needs no welding in a finished house.
- Welded: the cap plate is welded to the bottom flange on site. That needs a qualified welder and attention to fire safety in an occupied building.
- Clamped or bracketed: some products clip over the flange. Use only what the designer or manufacturer specifies.
Bolt holes have to line up, so plate holes and flange holes are best detailed together on the shop drawings when the beam and posts are ordered from the same fabricator. See types of steel beam to column connections for connection types beyond house basements.
Base plates and the footing
The base plate sits on the footing, not on the basement slab. Article 9.17.2.1. requires every column to be centred on a footing that conforms to Section 9.15. Typical arrangements:
- Plate on the footing, slab poured around it. Common in new construction. The column goes in before the slab, and the slab locks the base in place sideways.
- Plate anchored to an exposed footing or pedestal. The plate is drilled for anchors set into the concrete. This is common where a new footing is poured in an existing basement.
- Plate on a levelled bed. Where the footing surface isn't flat, the plate is set on a levelling bed or grout so it bears evenly.
The size of the footing itself comes from Table 9.15.3.4. for simple cases or from the engineer. Our guide to lally column footing requirements goes through it, and steel post base plates and concrete connections covers anchor and grout details.
Corrosion at the base
The bottom of a column is where rust starts, especially where it sits in a damp slab or in water from a leak or a sump overflow. A base plate that has rusted through, or a tube that's thin and flaking just above the slab, needs attention. Exterior steel columns must have at least one coat of rust-inhibitive paint (Article 9.17.3.3.), and keeping basement columns painted and dry is good practice too.
Loose plates vs welded plates
Columns come with plates attached in different ways:
| Plate type | How it works | Watch for |
|---|---|---|
| Both plates shop welded | Fabricated to a measured length | Needs an accurate field measurement |
| One plate welded, one loose | Column cut to length on site, second plate attached after | Cut must be square; plate must be properly fixed |
| Adjustable screw plate | Screw and nut at one end set the height | Label, maximum extension, screw locked |
| Loose plates under a plain tube | Plate simply placed under the column | Plate can shift; column isn't positively fastened |
A shop-welded post cut to a measured length is the most predictable option because the plate is square to the column and the weld is made under shop conditions. Our shop welding is certified by the Canadian Welding Bureau. One US evaluation report even requires special inspection where the loose end plate is field-welded after cutting, which shows how seriously the end connection is taken.
Plates fabricated with your posts
We fabricate steel posts for basements with base and cap plates welded on, plus separate base, cap and connection plates cut and drilled to your details. Send us your drawings or measurements for a quote, or see our steel products for what we supply. If you're replacing or adding a column, the design and permit come first: see how to install a lally column in a basement for what to expect.
Frequently asked questions
What size plate does a lally column need in Ontario?
Article 9.17.3.2. of the 2024 Ontario Building Code requires steel plates at least 100 mm by 100 mm by 6.35 mm thick at each end of a steel column. Under a wood beam, the top plate must extend across the full width of the beam.
Does a lally column need a top plate on a steel beam?
Not always. The code lets you omit the top plate where the column supports a steel beam and there is another provision for attaching the column to the beam, such as bolts or a weld to the flange.
How is a lally column attached to a wood beam?
Through the top plate, which runs the full width of the beam and is fastened up into it, often with screws or lags through holes in the plate, sometimes with side tabs or a U-shaped saddle. The fastener type and number come from the designer or the column maker's instructions.
Should the base plate sit on the slab or the footing?
On the footing. A column must be centred on a footing that conforms to Section 9.15. of the code. The base plate commonly sits on the footing below slab level and the slab is poured around the column.
