Engineered Wood Types: Panels, LVL, PSL, Glulam and CLT

Engineered wood is wood that has been cut into veneers, strands, particles or fibers, or into boards, and glued or fastened back together into a product with more predictable properties. Wikipedia sorts the types into three families, and the USDA Forest Products Laboratory's Wood Handbook (chapter 11) uses the same building blocks:

• Wood-based panels - plywood, oriented strand board (OSB), particleboard, medium-density fiberboard (MDF) and hardboard (high-density fiberboard).
• Structural composite lumber (SCL) - laminated veneer lumber (LVL), parallel strand lumber (PSL), laminated strand lumber (LSL) and oriented strand lumber (OSL).
• Mass timber and beams - glued laminated timber (glulam), cross-laminated timber (CLT), nail-laminated and dowel-laminated timber, plus prefabricated I-joists that combine SCL or lumber flanges with a panel web.

Engineered hardwood flooring is a fourth, consumer-facing group: a real wood top layer glued over a plywood, finger-jointed or fiberboard core.

Each panel is made from a different size of wood piece, and you can see that on a cut edge:

• Plywood - thin veneers with the grain of each layer turned across the one below it (Wikipedia). The edge shows stripes of alternating long grain and end grain.
• OSB - thin strands bonded with water-resistant resin, usually phenol-formaldehyde or pMDI. The USDA says the outer faces have longer strands aligned with the panel's length and the core is cross-aligned or random, which is why OSB is stiffer along its length. Aspen is the main North American species.
• Particleboard - sawdust, shavings and small particles. Unlike OSB, the USDA notes the faces are fine particles and the core is coarser, giving a smooth surface for laminating. It is the predominant material in ready-to-assemble furniture and is usually bonded with urea-formaldehyde.
• MDF and hardboard - wood broken down to fibers, mixed with wax and resin and pressed; hardboard is the denser version. The edge looks like uniform felt with no visible chips. Both are for non-structural use (Wikipedia).

The Wood Handbook describes SCL as small pieces of wood glued into sizes common for sawn lumber. Because knots and other defects are spread through the veneers or strands, SCL is often stronger and more reliable than a sawn board of the same size, spans farther and changes size less.

• LVL - veneers 1/8 to 1/10 in. thick, all laid in the same grain direction (plywood alternates them), hot-pressed with phenol-formaldehyde. Sheets are commonly 2 to 4 ft wide and 1-1/2 in. thick. Used for headers, beams, scaffold planks and I-joist flanges.
• PSL - veneer clipped into strands about 3/4 in. wide and at least 24 in. long, glued (commonly with phenol-resorcinol formaldehyde) and cured with microwaves. Sold as Parallam. Used for large beams and columns.
• LSL and OSL - an extension of OSB technology with longer strands; LSL strands are about 12 in. long. Sold as TimberStrand. Used for studs, rim and band joists and millwork.

The Handbook also warns that LVL and PSL are porous and can soak up water quickly if left unprotected on site.

Glulam is layers of dimension lumber glued with moisture-resistant adhesives; it can be made curved and, per Wikipedia, is stronger than steel pound for pound. CLT stacks whole layers of lumber at right angles to each other; Wikipedia gives panel sizes up to about 64 by 8 ft and up to 16 in. thick. CLT entered the International Building Code in 2015, and the 2021 code allows mass-timber buildings up to 18 stories (Type IV-A), 12 (IV-B) and 9 (IV-C). The downside Wikipedia lists for both is cost: they are more expensive than solid sawn timber.

There is no single answer, and anyone who gives you one number is quoting a particular product. The Wood Handbook says relatively high design values are assigned to both LVL and PSL, that LSL and OSL have somewhat lower values, and that no standard grades or design stresses exist for SCL: each manufacturer develops its own under ASTM D 5456, and the designer must use that manufacturer's published values. The practical difference is size. PSL comes as big billets (typically 11 by 19 in.) and is chosen for large beams and columns; LVL comes as 1-1/2 in. sheets that are ripped into headers and I-joist flanges and plied together for wider beams.

• Glue and formaldehyde. Wikipedia notes that cheap urea-formaldehyde resins can break down in moisture and release formaldehyde; phenol-formaldehyde forms water-resistant bonds; pMDI contains no formaldehyde. In the US, EPA's TSCA Title VI rule covers hardwood plywood, MDF and particleboard: products had to be certified from 1 June 2018, and products made or imported after 22 March 2019 must carry a TSCA Title VI compliant label. Look for that label on furniture and cabinets.
• Water. Particleboard swells and discolors when wet (Wikipedia); fiberboard-core flooring must be kept away from water and high humidity; unprotected LVL and PSL absorb water quickly (USDA).
• Cost. M.T. Copeland puts LSL at about three times the cost of dimensional lumber; glulam and CLT cost more than solid timber (Wikipedia).
• Energy and looks. Engineered products need more primary energy to make than solid wood (Wikipedia), and visible strands or chips are not to everyone's taste.

The part that decides stability is the core under the real-wood top layer. Wikipedia lists four cores: multi-ply wood with each ply turned across the next (the most common stable build), finger core made of small blocks set across the top layer, fiberboard core (MDF or HDF), and the European three-layer build with a softwood core and a backing layer. Fiberboard cores absorb moisture, so the same source says they must be kept away from water and high humidity; for kitchens, basements and humid climates a ply or finger core is the safer choice. The top layer can be flat-sawn, quartersawn or rift-sawn, which changes the look but not the core's behavior. Ask the maker how thick the wear layer is and how many times it can be sanded.

If you are trying to work out what a shelf, subfloor or beam is made of, photograph the cut edge square-on in good light, then a face. The edge tells the family (layers, strands, chips or felt-like fiber) and the face veneer, if any, tells the species. WoodLens can check the face species from a photo. For solid lumber, start with types of wood and types of plywood.

This page was drafted with AI help, and every figure was checked line by line against the sources listed.