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.
Fast Facts
- What Is It?
- PSL (Parallel Strand Lumber) is a high-strength engineered wood product made from long parallel strands of veneer bonded under heat and pressure, used for beams, headers, and columns where maximum strength is required.
- Common Uses
- Heavy-load beams, columns and posts, garage door headers, multi-story load-bearing applications, post-and-beam construction
- Cost Range
- $10–$20 per lineal foot (3-1/2" x 11-7/8")
- Durability
- Very durable structurally; moisture-resistant adhesive but not rated for permanent exterior exposure without treatment.
Specifications
| Property | Value |
|---|---|
| Manufacturing Standard | ASTM D5456 |
| Common Sizes (Beams) | 3-1/2" x 7" to 7" x 18" |
| Common Sizes (Columns) | 3-1/2" x 3-1/2" to 7" x 7" |
| Allowable Bending Stress (Fb) | 2,900 psi |
| Modulus of Elasticity (E) | 2.0 million psi |
| Compression Parallel to Grain (Fc) | 2,900 psi |
| Weight | Approximately 45 pcf (heavier than LVL or glulam) |
| Manufacturer | Weyerhaeuser (Parallam PSL) |
What Is PSL?
Parallel strand lumber represents the highest-strength category of structural composite lumber products. Developed by MacMillan Bloedel (now Weyerhaeuser) in the 1980s and commercialized as Parallam PSL, it is manufactured from long, thin strands of Douglas Fir or Western Hemlock veneer — typically 8 feet long and about 1/2 inch wide. These strands are coated with waterproof phenol-formaldehyde adhesive, aligned parallel, and pressed into solid billets under massive hydraulic pressure.
The resulting material has a distinctive straw-like appearance on the end grain and a striated pattern on the face. PSL is noticeably heavier than LVL or solid lumber — at approximately 45 pounds per cubic foot, it is about 20% heavier than LVL. This density contributes to its exceptional strength and stiffness properties.
When PSL Is the Right Choice
- Heavy point loads: When a single column supports multiple floor levels or carries concentrated loads from beams, PSL provides the highest compression capacity in the smallest cross section.
- Wide beam applications: PSL is manufactured in widths up to 7 inches without multi-ply lamination. A single 7" x 11-7/8" PSL beam is simpler and more reliable than a quad-ply LVL assembly.
- Post-and-beam construction: PSL columns and beams create a unified engineered wood system with consistent appearance and predictable connections.
- Garage door headers: The heavy loads above garage doors (often supporting a second floor plus roof) can be handled with a smaller PSL member than LVL or glulam, potentially allowing a shallower header that provides more garage clearance.
Design and Specification
PSL is specified using Weyerhaeuser design software (ForteWEB) or published load tables. Because PSL is a proprietary product with specific tested properties, generic engineered wood span tables do not apply. The designer must use Parallam-specific design values.
One unique advantage of PSL is its high compression strength. At 2,900 psi allowable Fc, a 3-1/2" x 3-1/2" PSL column can support approximately 29,000 pounds in a short-column application — far more than a 4x4 solid lumber post of any species.
Installation Notes
- PSL is heavy — plan accordingly. A 3-1/2" x 11-7/8" x 16-foot PSL beam weighs approximately 120 pounds. Longer beams may require mechanical lifting.
- Fastening to PSL follows standard engineered wood practices — use Simpson Strong-Tie or equivalent engineered connectors. Do not rely on toenailing for structural connections.
- Field cutting is done with standard carpentry tools, though carbide-tipped blades are recommended due to PSL density and adhesive content.
- Like all engineered wood, PSL should be protected from sustained moisture during construction. Store under cover and wrap exposed members.
Frequently Asked Questions
What is PSL used for?
PSL is used for structural beams and columns where maximum load-carrying capacity is required. Common applications include garage door headers over wide openings, columns supporting heavy point loads, multi-story bearing posts, and post-and-beam construction. PSL is often specified when the load exceeds what LVL or glulam can carry in the available space.
How does PSL compare to LVL?
PSL has approximately 10-15% higher bending strength than LVL and significantly higher compression strength, making it superior for columns and posts. PSL is also available in wider widths (up to 7" as a single piece) compared to LVL standard 1-3/4" width. The trade-off is cost — PSL typically costs 50-100% more per lineal foot than LVL. PSL is also heavier, at roughly 45 pcf versus 37-40 pcf for LVL.
Is Parallam the same as PSL?
Yes. Parallam is the brand name for PSL manufactured by Weyerhaeuser. It is the dominant PSL product in North America and currently the only widely available PSL product. The terms Parallam and PSL are used interchangeably in the industry, though PSL is the generic technical term.
Can PSL be used as a column?
Yes — PSL is one of the best engineered wood materials for columns. It has high compression parallel-to-grain strength (2,900 psi), is available in square cross sections (3-1/2" x 3-1/2" up to 7" x 7"), and its bonded-strand construction distributes loads uniformly. PSL columns are commonly used under LVL or glulam beams at bearing points.
Related Guides
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.
LSL (Laminated Strand Lumber)
Laminated strand lumber (LSL) is an engineered wood product made from flaked wood strands aligned and bonded with structural adhesive. Known commercially as TimberStrand LSL (Weyerhaeuser), it is used for headers, rim board, studs, and plates where dimensional stability and long lengths are valuable.
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.