Solid dimensional lumber such as 2x4s and 2x6s is fully reusable if it is not rotted or badly damaged, and exterior plywood is worth keeping while its layers remain bonded, but OSB, particleboard and any panel that has been soaked swell and crumble and are generally not worth carrying. Laminated veneer beams and I-joists are valuable for spanning distances only while they are intact, and preservative-treated wood must not be burned.
Part of Building Material Recovery
Modern buildings mix solid wood with glued, layered and chipped products, and they react to water, nails and reuse in very different ways. Telling them apart on sight is the skill.
Reusability Falls As The Product Gets More Processed
Dimensional lumber (2x4s, 2x6s, 2x8s and so on) is solid wood and fully reusable if not rotted or severely damaged. Old-growth lumber from pre-1970 buildings is often better than new lumber, with tighter grain, higher density and more resistance to warping, and is worth recovering even with surface wear (parent article).
Plywood is reusable if it has not delaminated, that is, if its layers have not separated. CDX (exterior grade) plywood with intact edges is valuable for subfloor, sheathing and general-purpose panels. Interior plywood that has been exposed to water is usually delaminated and not worth carrying.
OSB (oriented strand board) is the pressed-wood panel used in modern construction. It does not survive water: it swells, crumbles and loses structural value when wet. It is generally not worth salvaging unless completely dry and intact.
LVL and engineered beams. Laminated veneer lumber and I-joists are stronger than dimensional lumber per unit weight. If intact, they are very valuable for spanning distances. If any delamination is visible, the piece is compromised.
Particleboard and fibreboard. Chipped or fibre panels used in cabinets and shelving swell when wet and hold fasteners poorly; keep only dry, intact pieces for light use.
Treated lumber. Pressure-treated wood, with a greenish tint from a copper-based preservative, is rot-resistant but should not be burned (toxic fumes from copper arsenate in older wood) or used in food-contact applications (parent article).
What You Need
- Good light and a straightedge.
- An awl or knife.
- A tape, for measuring real as opposed to nominal sizes.
- Eye protection and gloves.
Method: Identify The Product, Then Test Its Weak Point
Step 1: Identify. Solid wood shows continuous grain across the end; plywood shows thin layers with alternating grain; OSB shows flakes; LVL shows many thin parallel layers; I-joists have a thin panel web between two flanges.
Step 2: Test the weak point of each.
- Solid wood: awl for rot, sight for warp (see Assessing Wood Condition).
- Plywood: look at the edges for lifting layers and bubbles on the face; press and flex a corner.
- OSB: check edges and corners for swelling and crumbling.
- LVL and I-joists: look at glue lines and the web for separation.
Step 3: Sort. Solid lumber by size and grade; panels by thickness; engineered beams by length; treated wood apart from the rest, labelled.
Step 4: Match to the job. Use sound solid lumber and intact engineered beams for load; use plywood for sheathing; keep OSB for dry, non-structural use.
Common Mistakes
- Treating nominal sizes as real sizes. A “2x4” is smaller than 2 by 4 in finished dimensions; measure.
- Carrying swollen OSB for kilometres. It has no strength.
- Burning treated wood as fuel. The fumes are toxic.
- Cutting an I-joist’s web or flange for pipes. It weakens the whole piece.
Safety
Treated wood smoke and failed beams are the two serious risks
Do not burn pressure-treated wood or use it in contact with food or for cooking surfaces; its fumes are toxic. A delaminated engineered beam or a swollen panel in a floor or roof can fail without warning, so use only intact pieces in load-bearing roles and proof-test with people clear. Wear gloves and a respirator when cutting old composite panels, since their dust and glue residues are irritants.
What’s Next
- Learn next: Metal Recovery & Processing — the next material in the building
- Combine with: Assessing Wood Condition — the tests applied to solid timber