Sizing Headers and Lintels the Way the OBC Actually Reads Them

A Red Seal Carpenter sizing the header over a new patio door or kitchen pass-through is not eyeballing 2×8s versus 2×10s — the Ontario Building Code gives hard numbers in Section 9.23.12.3 and the tables are organized differently from the beam tables framers are used to. Here is how to walk through the columns correctly, pick the right species and ply count, land the header on enough bearing, and recognize when a 2× lintel stops being enough and an LVL or engineered beam has to take over.

The column that trips most framers: snow load

Every lintel span in Tables 9.23.12.3.-A through -C is indexed along the top by specified ground snow load in kilopascals — 1.0, 1.5, 2.0, 2.5, and 3.0 kPa. That single column choice can drop your allowable span by 35 percent from left to right. Toronto is 1.0 kPa. Ottawa is 2.4 kPa. Sudbury is 2.8 kPa. Parry Sound is 3.2 kPa. Thunder Bay is 1.8 kPa. OBC Appendix C publishes the value for every municipality in the province, and most local building departments will tell you the number over the phone if you ask. Using the wrong snow-load column is one of the most common header mistakes in framing — a 2-ply 2×10 SPF at 4.9 m tributary spans 2.88 m at 1.0 kPa but only 2.01 m at 2.5 kPa, a loss of almost three feet of opening for nothing but picking the wrong column. Confirm your municipality's snow load first, then walk into the table.

The row that trips most framers: what sits above

The left-hand column of each lintel table lists six distinct loading scenarios and they all give different spans: Limited attic storage and ceiling (interior walls only — no exterior column), Roof and ceiling only, 0.6 m tributary (narrow strip of roof — gable end walls where no rafters bear), Roof and ceiling only, 4.9 m tributary (the normal case — an exterior wall that rafters or trusses actually bear on), Roof, ceiling and 1 storey (a full floor lands on this wall), Roof, ceiling and 2 storeys, and Roof, ceiling and 3 storeys. A 2-ply 2×10 in SPF No.1/No.2 at 2.0 kPa snow spans 2.20 m under roof-and-ceiling only, 1.89 m under roof + ceiling + 1 storey, 1.72 m under two storeys, and 1.62 m under three. Picking the right row requires looking up through the ceiling — if you can see floor joists running perpendicular across the top plate, you are in a "+1 storey" situation minimum. A ranch with a walk-up attic and no floored storage is "Roof and ceiling only." A bungalow ceiling with attic storage feeds the interior-walls column via Note (3) reductions.

Species and grade matter — pick one, use its table

The OBC publishes three separate lumber lintel tables because species strength varies materially: Douglas Fir-Larch (Table -A) is strongest, Hem-Fir (Table -B) sits in the middle, and Spruce-Pine-Fir (Table -C) is most common in Ontario yards but about 5 to 8 percent weaker than D.Fir-L at the same size. All three tables assume No.1 or No.2 grade — the grade stamp on every piece of framing lumber you buy. Do not default to the strongest species on your spreadsheet; grab a board off the pile and read the stamp, then use that species' table. If the stamp says a species group not listed (Northern Species, for example), the conservative move is to use the SPF table and accept roughly 85 to 90 percent of its values, or upgrade to D.Fir-L for a clean match. Ply count multiplies the capacity: a 3-ply built-up is roughly 1.22 times a 2-ply, and a 4-ply is roughly 1.41 times — use this to hit opening widths the 2-ply cannot reach without going to a deeper member.

Fastening and framing the opening

OBC 9.23.12.2.(2) is specific about how lintel plies lock together: 82 mm (3-1/4″) nails in a double row, with nails not more than 450 mm apart in each row. Short nails, single-row, or 600 mm spacing do not satisfy the code — the plies will not share load and the lintel will deflect like individual members. Every opening needs a king stud on each side running full height from bottom plate to top plate, with the header's jack stud nailed to the king's face. Openings up to about 1.22 m (4 feet) take one jack per side; wider openings typically take two jacks per side because the header is now delivering enough load that a single 38 mm jack is overstressed in compression perpendicular to grain. Above the header, cripples run from the header top up to the top plate, spaced on the regular stud layout (16″ or 24″ o.c.) so that continuous sheathing and top-plate attachment are maintained. Skipping cripples on a short header-to-plate distance is a rookie mistake — the wall loses its diaphragm continuity right where it needs it most.

Bearing length — the small number that causes the big problem

Every span in Tables 9.23.12.3.-A through -C is clear span between supports. The rough opening is the clear span plus two bearing lengths. OBC 9.23.12.3 Note (4) sets the minimums: sawn-lumber lintels spanning up to 3 m need at least 38 mm of bearing at each end; lintels spanning greater than 3 m need at least 76 mm. Glulam lintels always need at least 89 mm. LVL follows manufacturer direction — typically 89 to 140 mm. The reason the code is fussy here is crushing: residential framing lumber has a perpendicular-to-grain compression allowable around 4.6 MPa, and a header on 38 mm of bearing is funneling every pound of roof and snow load through a strip about 4,300 mm² of wood fibre. Short bearing leads to visible settlement, drywall cracks above the header, and doors that stop latching a winter later. On wider openings with doubled jacks, you automatically get 76 mm of bearing (two 38 mm members) — one of several reasons wider openings take two jacks.

When 2× lumber stops being enough — glulam, LVL, and engineered flitch

Part 9 lumber lintels top out around 3.6 m opening width for realistic loads. Past that, move to glulam under Table 9.23.12.3.-D (20f-E grade, widths of 80 mm or 130 mm, depths 304 to 532 mm) or to LVL from a manufacturer's span table. LVL is not in the OBC — it is engineered and every manufacturer publishes a stamped span chart by snow-load region. Your supplier will hand you the chart; pick the depth and ply count that covers your opening plus the load above, and follow manufacturer bearing and fastening rules (16d nails in two rows for 2-ply, through-bolts for 3+ ply). For very long spans or heavy point loads — a steel post landing from the storey above, or a floor girder flush-framing into the lintel — you are outside Part 9 span tables entirely and a P.Eng. needs to design the beam. A stamped drawing covers the builder, the client, and the inspector. A header that sags 20 mm at mid-span costs far more to replace once the drywall is on.