A base plate is a steel plate welded to the bottom of a steel column that spreads the column's load into concrete. A sill plate is the wood member anchored to the top of a foundation wall that the floor framing sits on. A sole plate is, in Canadian framing, the bottom wood plate of a stud wall; in steel and bridge work the same term can mean a steel plate welded under a beam where it sits on a bearing. Base and bearing plates are steel and carry concentrated loads; sill and sole plates are usually wood and carry walls and floors along their length.
The confusion comes from the same words meaning different things in different trades and countries. Here's how to keep them straight.
The plates at a glance
| Plate | Material | Where it sits | What it does |
|---|---|---|---|
| Base plate | Steel | Under a steel column or post | Spreads the column load into concrete; holds the column with anchor rods |
| Cap plate | Steel | On top of a column | Gives the beam above a bearing and connection surface |
| Bearing plate | Steel | Under a beam end on concrete or masonry | Spreads the beam reaction so the support isn't crushed |
| Sole plate (steel) | Steel | Welded to a beam's bottom flange at a bearing | Gives the beam a flat, stiff surface on its bearing or masonry plate |
| Sole plate (wood framing) | Wood | Bottom of a stud wall, on the subfloor | Holds the studs and ties the wall to the floor |
| Sill plate | Wood | Top of the foundation wall | Levels and anchors the floor framing to the foundation |
Base plates: steel column to concrete
A base plate is the foot of a steel column. It's welded to the column in the shop, set on a footing, pier or slab over anchor rods, levelled and grouted. It does three jobs:
- Spreads the load. Concrete can't take the concentrated stress of a column's cross-section directly, so the plate enlarges the contact area.
- Holds the column in place. Anchor rods resist uplift and sliding and, in fixed bases, bending.
- Gives a level start. The column's plumbness depends on the plate being set level at the right elevation.
In a house, the 2024 Ontario Building Code (Sentence 9.17.3.2.(1)) requires steel columns to have plates of at least 100 mm x 100 mm x 6.35 mm at each end. Larger buildings use engineered plates. For more, see what a column base plate is and base plate vs end plate vs gusset plate.
Sole plates: two trades, two meanings
In wood framing
In Canadian and US framing, the sole plate is the bottom plate of a stud wall: the horizontal member the studs are nailed to at the bottom, which is then nailed down through the subfloor into the joists or blocking. The 2024 OBC uses both names together, "bottom wall plate or sole plate", in its framing nailing rules (Article 9.23.3.4). It carries the wall's load along its length and keeps the bottom of the wall in line.
In steel and bridge work
In steel bearings, a sole plate is a steel plate welded to the underside of a beam or girder at its bearing. It stiffens the flange locally, gives a flat, level surface to sit on the bearing or masonry plate below, and can be bevelled to take up slope. The plate it sits on, anchored to the concrete, is often called the masonry plate. You'll see this pairing on bridge drawings and on some heavier building beams that sit on concrete or masonry rather than on columns.
In UK usage
British sources often use "sole plate" for the timber laid on the foundation, which Canadians call a sill plate. If a reference seems to describe a sill plate under the name sole plate, check where it's from.
Sill plates: wood framing to the foundation
The sill plate is where a wood-framed house meets its concrete foundation. The floor joists or rim joist sit on it, and it's bolted down to the foundation wall. The 2024 OBC sets out the basics in Part 9:
- Size. Where the sill plate provides bearing for the floor system, it must be at least 38 mm by 89 mm (Sentence 9.23.7.1.(1)).
- Levelling. It is either set on a full bed of mortar or laid directly on the foundation where the top is level (Sentence 9.23.7.2.(1)).
- Sealing. The joint between the sill plate of an exterior wall and the foundation has to be sealed for air leakage (Sentence 9.23.7.2.(2)).
- Anchorage. Unless a structural analysis shows otherwise, building frames are anchored to the foundation; one of the standard methods is fastening the sill plate with anchor bolts of at least 12.7 mm diameter at no more than 2.4 m on centre (Sentence 9.23.6.1.(2)), with other requirements in higher wind and seismic areas.
- Dampness. Wood that isn't pressure-treated and sits on concrete in contact with the ground has to be separated from it by polyethylene film or roll roofing, unless it's at least 150 mm above the ground (Article 9.23.2.3).
Note the parallel with a base plate: both spread load onto concrete and are anchored to it. The difference is that a sill plate carries a wall and floor along its whole length, while a base plate carries one column at one point.
Bearing plates: where steel beams sit on concrete or masonry
A bearing plate goes under the end of a steel beam where it rests on a foundation wall, pilaster or masonry pier. Like a base plate, its job is to spread a concentrated reaction so the material below isn't crushed, and to give the beam a level seat at the right elevation. It may be loose (set in grout or mortar), anchored with studs or rods, or welded to the beam.
When a beam sits in a pocket in a foundation wall, the bearing length and the support under it are set by the code or the designer. Our post on steel beam bearing length on concrete and masonry covers the requirements, including when a bearing plate is added.
How the plates meet in a typical house
Picture a basement with a steel beam on steel posts and a wood-framed house above:
- Each steel post sits on a footing on its base plate, and carries the beam on its cap plate.
- The beam ends sit in pockets in the foundation wall, sometimes on bearing plates.
- The beam usually has a wood top plate (nailer) bolted to its top flange so the joists can be fastened to it; see attaching a wood top plate to a steel beam.
- Around the perimeter, the floor joists sit on the sill plate on the foundation wall.
- The walls above stand on their sole plates on the subfloor.
Five different plates, three of them steel, all doing versions of the same job: spreading load and tying one part of the building to the next. If you're installing a steel beam in a basement, your drawings should show the steel plates; the wood plates are framing.
Steel plates made to your drawings
We cut and drill base plates, cap plates, bearing plates and connection plates to your details, and supply HSS and steel posts with base and cap plates welded on. Our welding is CWB certified, shop drawings are prepared in house, and we can prime or galvanize to suit. Send your drawings or a plate list for a free take-off and quote.
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Frequently asked questions
What is the difference between a base plate and a sole plate?
A base plate is a steel plate welded to the bottom of a column that spreads its load into concrete. A sole plate is usually the bottom wood plate of a stud wall in Canadian framing; in steel and bridge work, it can also mean a steel plate welded to a beam's bottom flange where the beam sits on a bearing.
Is a sill plate the same as a sole plate?
Not in Canadian practice. The sill plate is the wood member anchored to the top of the foundation wall, and the floor framing sits on it. The sole plate (bottom plate) is the bottom member of a framed wall, nailed down to the subfloor. In the UK, 'sole plate' is often used for what Canadians call a sill plate.
What is the difference between a base plate and a bearing plate?
A base plate is attached to the bottom of a column. A bearing plate sits under the end of a beam where it rests on concrete or masonry, spreading the beam's reaction so the support isn't crushed. Both spread load into a weaker material below.
What size does a sill plate have to be in Ontario?
Under Sentence 9.23.7.1.(1) of the 2024 Ontario Building Code, a sill plate that provides bearing for the floor system must be at least 38 mm by 89 mm (a 2x4). It is levelled on mortar or laid directly on a level foundation, and anchored to the foundation.
