Steel Beams (Flitch Plates & W-Shapes)
Structural steel beams — including W-shapes (wide-flange), S-shapes, and flitch plates — carry heavy point loads and long spans in residential and commercial construction. Often specified where wood alone cannot meet load or deflection requirements.
Fast Facts
- What Is It?
- Hot-rolled or built-up steel members used as headers, girders, and ridge beams where high load capacity or long spans are required.
- Common Uses
- Open floor plans (load-bearing wall removal), garage door headers, ridge beams in cathedral ceilings, multi-story support columns.
- Cost Range
- $8–$25 per linear foot for W-shapes; flitch plates $4–$12/LF plus lumber.
- Durability
- Essentially unlimited indoors. Exterior requires galvanizing or primer + paint. Fire-rated assemblies require intumescent coating or encasement.
Specifications
| Property | Value |
|---|---|
| Common Residential Sizes | W8×10 through W12×26; S6×12.5 through S10×25.4 |
| Yield Strength | ASTM A992 Grade 50 (50 ksi) for W-shapes; A36 (36 ksi) for plates |
| Flitch Plate | 1/4"–1/2" steel plate sandwiched between two LVL or dimensional lumber members |
| Deflection Limit | L/360 for floor beams; L/240 for roof beams per IRC |
| Fire Rating | Unprotected steel: 0 hours. Requires encasement or intumescent coating for rated assemblies. |
| Weight | 10–26 lb/ft for common residential W-shapes |
When to Specify Steel
Steel beams are the default solution when engineered lumber products like LVL, glulam, or PSL cannot meet the load or span requirements within the available depth. Common triggers include removing a load-bearing wall in a renovation, supporting a concentrated point load from above, or spanning a garage door opening wider than 16 feet.
Types of Structural Steel Beams
W-shapes (wide-flange) are the most common structural beam profile, with wide parallel flanges that resist bending efficiently. S-shapes (American Standard) have tapered flanges and are less common in new construction. Flitch plates combine a steel plate with wood members, offering a cost-effective middle ground between all-wood and all-steel solutions.
Connection Details
Steel beams require engineered bearing plates at support points — typically 1/2" steel plate on concrete or masonry piers. Wood-to-steel connections use through-bolts, welded knife plates, or proprietary connectors. All connection details must be specified by the structural engineer and shown on the plans.
Corrosion Protection
Interior steel beams in dry environments need only a coat of primer. Exposed or damp-area beams require hot-dip galvanizing (ASTM A123) or a zinc-rich primer system. In coastal environments, specify weathering steel (Cor-Ten / ASTM A588) or stainless steel connections.
Frequently Asked Questions
When should I use a steel beam instead of an LVL?
Use steel when the required load exceeds LVL capacity for the available depth, when you need a shallower beam to maintain headroom, or when spans exceed 20–24 feet. An engineer must size all steel beams.
What is a flitch plate beam?
A flitch plate is a steel plate (typically 1/4" to 1/2" thick) bolted between two wood members. It combines the ease of wood framing connections with added steel strength. Common for headers and short beams where a full W-shape is overkill.
Do steel beams need fireproofing in residential construction?
In most single-family homes, steel beams in basements and crawl spaces do not require fireproofing. However, beams in fire-rated assemblies (attached garages, multi-family separations) require intumescent coating, gypsum encasement, or spray fireproofing per IBC/IRC.
Can I cut a steel beam on site?
Steel beams should be ordered cut to length from the supplier. Field cuts require a metal-cutting band saw, reciprocating saw with bi-metal blade, or oxy-fuel torch. Any field modifications must be approved by the structural engineer.
Related Guides
Comparisons Featuring This Material
Also Consider
LVL (Laminated Veneer Lumber)
Laminated veneer lumber (LVL) is a high-strength engineered wood product made from thin wood veneers bonded with structural adhesive under heat and pressure. It is the most commonly specified engineered beam and header material in residential and light commercial construction.
Glulam (Glued Laminated Timber)
Glulam (glued laminated timber) is a structural engineered wood product made by bonding multiple layers of dimensional lumber with waterproof adhesive. Available in architectural and industrial grades, glulam is used for beams, columns, arches, and exposed structural applications where both strength and appearance matter.
PSL (Parallel Strand Lumber)
Parallel strand lumber (PSL) is a high-strength engineered wood product made from long, thin strands of wood veneer bonded with waterproof adhesive under high pressure. Known commercially as Parallam PSL (Weyerhaeuser), it is used for beams, columns, and posts where maximum load-carrying capacity is required.