A built-up beam is two or more layers of 2-inch lumber nailed face to face so they act as one member. 2021 IRC Table R602.3(1), item 28, sets the nailing at the top and bottom of each layer, with extra nails at the ends and at every splice.
A built-up girder is the same thing under another name: a beam made by fastening dimension lumber plies together instead of cutting one solid timber. The 2021 International Residential Code (IRC) covers sawn-lumber plies only. The code edition your jurisdiction has adopted, plus any local amendments, governs, and engineered members such as laminated veneer lumber (LVL) follow the manufacturer's instructions.
Key facts
- Under 2021 IRC Table R602.3(1), item 28, each layer of a built-up girder or beam of 2-inch lumber is nailed with 20d common (4 inch by 0.192 inch) nails at 32 inches on center at the top and bottom, staggered.
- Under 2021 IRC Table R602.3(1), item 28, the schedule also lists 10d box or 3-inch by 0.131-inch nails at 24 inches on center, face nailed at the top and bottom, staggered on opposite sides.
- Under 2021 IRC Table R602.3(1), item 28, ends and splices are face nailed with 2-20d common, 3-10d box or 3-3-inch by 0.131-inch nails.
- Under 2021 IRC Section R502.6, a beam or girder end has at least 1-1/2 inches of bearing on wood or metal, or at least 3 inches on masonry or concrete.
- Under 2021 IRC Section R502.5, spans of dimension-lumber girders and headers come from Tables R602.7(1), R602.7(2) and R602.7(3).
- Under 2021 IRC Section R502.1.5, structural composite lumber capacities are established under ASTM D5456, so LVL plies follow the manufacturer, not item 28.
How do you build a built up beam?
Build it from the table down: size first, then nailing, then bearing.
- Get the size from the span table. Table R602.7(1), R602.7(2) or R602.7(3) gives the ply count and lumber size for a span, load and building width. The sizes are written as plies by lumber size, so 2-2 x 10 is two 2x10s. Spans are in the header size chart, and are not repeated here.
- Cut the plies to length. Any joint in a ply is a splice and needs the end and splice nailing covered below.
- Nail each layer. Follow item 28 in the table below, nailing top and bottom, staggered.
- Nail the ends and each splice with the extra face nails the same row requires.
- Set the ends on bearing that meets Section R502.6, with a post, column or wall under each end.
- Connect it. Where post-and-beam construction supports floor framing, Section R502.9 requires positive connections against uplift and lateral displacement.
- Land the joists. Joists framing into the side of a wood girder sit on approved framing anchors or ledger strips of at least nominal 2 by 2 inches (R502.6.2).
What nails and spacing does a built up beam need?
Nailing is set by Table R602.3(1). Item 28 covers girders and beams, and item 10 covers a built-up header with a spacer.
2021 IRC Table R602.3(1), items 28 and 10, as printed. In the table, the 32-inch spacing is set beside the 20d common nail, and the 24-inch spacing beside the 10d box and 3-inch nails. Confirm the pairing against the printed row.
| Item | Member | Fastener | Spacing and location |
|---|---|---|---|
| 28 | Built-up girder or beam, 2-inch lumber layers | 20d common (4 in. x 0.192 in.) | Nail each layer 32 in. on center at top and bottom, staggered |
| 28 | Same | 10d box (3 in. x 0.128 in.) or 3 in. x 0.131 in. nails | 24 in. on center, face nail at top and bottom, staggered on opposite sides |
| 28 | Same, at ends and splices | 2-20d common, or 3-10d box, or 3-3 in. x 0.131 in. nails | Face nail at ends and at each splice |
| 10 | Built-up header, 2-inch to 2-inch with 1/2-inch spacer | 16d common (3-1/2 in. x 0.162 in.) | 16 in. on center each edge, face nail |
| 10 | Same | 16d box (3-1/2 in. x 0.135 in.) | 12 in. on center each edge, face nail |
Nails are smooth common, box or deformed shanks unless the table says otherwise, and the table's footnotes set minimum bending yield strengths for framing nails. Header anatomy is shown in wall framing basics.
How far can a built up beam span?
The span depends on the size, the number of plies, what the beam supports, snow load and building width, and it comes from the tables, not from a rule of thumb. Table R602.7(1) lists sawn-lumber girder and header sizes from single 2x6 members up to four-ply members such as 4-2 x 12. Section R502.5 sends floor girders to the same tables.
One footnote matters for beams: the spans assume the top of the girder or header is laterally braced by perpendicular framing. Where it is not, tabulated spans for 2x8, 2x10 and 2x12 sizes are multiplied by 0.70, or the member is designed. Deck beams use a different table; see the deck beam span chart.
How much bearing does a built up beam need?
At least 1-1/2 inches on wood or metal, or at least 3 inches on masonry or concrete, unless approved joist hangers carry the member (R502.6). Where a beam bears on masonry or concrete, the bearing is direct or on a sill plate of 2-inch minimum nominal thickness, and that sill plate must provide a minimum nominal bearing area of 48 square inches.
The post or column below the beam is a separate part of the load path. Columns, including steel columns, are covered in the lally column guide, and the whole load path from roof to footing is drawn in the house framing diagram.
Where do splices go in a built up beam?
The code text used here requires face nails at each splice (Table R602.3(1), item 28) but does not state where splices must be located. Do not guess. Ask the designer or your building official where joints in the plies may fall, and read the span table notes for the member you chose. Section R502.6.1 on joists lapping over a bearing support covers floor joists, not beam plies.
Can you build up LVL or glulam beams?
Yes, but not by following item 28. Engineered members are fastened and sized under their own rules.
Which source governs each beam type under the 2021 IRC.
| Beam type | Code reference | Nailing and sizing source |
|---|---|---|
| Built-up 2-inch sawn lumber | R502.5, Table R602.3(1) item 28 | IRC span tables and nailing schedule |
| Structural composite lumber (LVL) | R502.1.5 | Manufacturer's tables and fastening instructions |
| Glued laminated timber | R502.1.3 | Manufacturer's tables, product made to ANSI A190.1 |
A multi-ply LVL beam is connected ply to ply as the manufacturer's instructions say. Have those instructions on site.
Does a beam near concrete need treated wood?
Sometimes. Under Section R317.1, wood girders in crawl spaces or unexcavated areas within the foundation periphery need durable or treated wood where closer than 12 inches to exposed ground (item 1), and the ends of wood girders entering exterior masonry or concrete walls need it where clearances are less than 1/2 inch on tops, sides and ends (item 4). The ground contact lumber guide lists every R317.1 location, and the basement wall framing guide shows the same rule applied to a wall.
What this article does not cover
Point loads, notching or boring a beam, uplift design and beams carrying more than the table assumes need engineering. The tables quoted are prescriptive limits for their stated conditions only.
Summary
A built-up beam is 2-inch plies nailed per Table R602.3(1), item 28, at the top and bottom of each layer, with extra nails at ends and splices. Size comes from Tables R602.7(1) to R602.7(3), and each end needs bearing under Section R502.6. LVL and glulam follow the manufacturer. Local amendments may change any of this.
Show the beam on your framing plan
Framing Plan is a preliminary drawing aid: it draws joist layouts, beams and openings and exports PNG, PDF and DXF. Its sample span profile uses demo figures and the editor works in millimetres, so it does not size beams or check code. Open the framing studio to place a beam in your joist layout, then have it sized for your project.