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Key points

  • Wood absorbs and loses moisture until it balances with the surrounding air humidity, swelling and shrinking as it does.
  • USDA Wood Handbook: most in-service moisture changes lie between 6% and 14%, where shrinkage is roughly proportional to moisture.
  • Engineered panels (MDF, plywood, particleboard) are usually bonded with formaldehyde-based adhesives; in the US they must carry a TSCA Title VI compliance label.
  • Termite protection starts before the slab is poured: soil treatment with an approved termiticide under the slab and around foundations, and a ventilation space between soil and wood.
Written for:OwnerContractorSupplier

Wood is still "alive" after it's cut: it breathes moisture from the air and moves with it. Understanding this explains many problems with doors, floors and cabinets.

1) Wood and moisture

The Wood Handbook published by the US Department of Agriculture's Forest Products Laboratory (USDA FPL) explains1:

  • Wood always tends towards equilibrium with the relative humidity of the surrounding air.
  • Most in-service moisture content changes lie in the range 6% to 14%, where the relationship between shrinkage and moisture is linear.
  • Proper drying, storage and handling reduce moisture change after installation; if moisture is kept within reasonable limits, most dimensional problems can be avoided.
In practice: store timber and wood flooring inside the space where it will be installed (air-conditioned and closed) before installation per the manufacturer's instructions, and leave expansion gaps at the walls for wood floors.

2) Solid wood and engineered panels

TypeDescriptionNotes
Solid woodPieces cut from the trunk.Natural beauty; moves more with humidity.
PlywoodThin veneers glued with cross-laid grain.Good dimensional stability and strength.
MDFWood fibres pressed with adhesive.Excellent smooth surface for painting and shaping; sensitive to water unless moisture-resistant.
ParticleboardWood particles pressed with adhesive.Economical, common in covered furniture and cabinets.

Formaldehyde

Engineered panels are often made with urea-formaldehyde adhesives, which emit formaldehyde into indoor air2. So the US set emission standards:

  • California's CARB ATCM Phase 2, followed by the federal TSCA Title VI with the same emission limits2.
  • It covers hardwood plywood, MDF, particleboard and products made from them, and since 22 March 2019 these products in the US must carry a TSCA Title VI compliance label3.

When buying cabinets, doors or furniture made from engineered panels, ask for a certificate of compliance with a recognised emission standard (such as TSCA Title VI, CARB P2 or equivalent European classes), and ventilate well after installation.

3) Termites

Subterranean termites reach wood through mud tubes from the soil. Recommended measures include:

  • Soil treatment with an approved termiticide under the slab and around foundations before pouring, by a pest control operator, with documentation4.
  • Baiting and monitoring systems as an alternative or supplement4.
  • Leaving a ventilation space between soil and wood during construction, and covering exposed wood with a sealant or metal barrier5.
  • Not piling firewood or wood debris next to the building, and not planting trees and shrubs against exposed wood5.
  • An annual inspection for mud tubes on foundations4.

The source stresses that termite treatment is not a job for the homeowner, as it needs specialised equipment and materials4.

4) Storage, protection, odours and indoor air

  • Storage: wood gains and loses moisture until it balances with the surrounding air, swelling and shrinking as it does1; store it covered and dry, close to the conditions of the installation space, before installing (practical tip).
  • Protection: outdoor or ground-contact wood needs suitable treatment and finishes, and termite prevention starts before construction. See Building pests.
  • Odours and indoor air: composite panels are often bonded with formaldehyde-based resins (Section 2)2; ventilate after new furniture is installed and ask for proof of emissions compliance. See Indoor air.
  • Marketing claims: "water-resistant" or "eco-friendly" without a specification or certificate is not enough; ask for the data sheet. See Comparing materials.

5) Before buying and installing

  1. Identify the location — wet (kitchen/bathroom) or dry — and choose a moisture-resistant panel where needed.
  2. Ask about the moisture content of solid wood and how it was dried.
  3. Ask for a formaldehyde emission certificate for engineered panels.
  4. Ask for a soil termite treatment certificate for new builds, with the warranty period.

Sources

The number next to a statement points to its source in this list. Sources back the general information; anything marked “practical advice” is editorial experience, not a quoted source. Anything that affects safety, structural design or electrical installations needs a licensed professional, and in Saudi Arabia the binding reference is the Saudi Building Code.

  1. 1Wood Handbook — Drying and Control of Moisture Content and Dimensional Changes — USDA Forest Products Laboratory
  2. 2Formaldehyde Emission Standards for Composite Wood Products in US (CARB ATCM Phase 2 and EPA TSCA Title VI) — International Committee of the Decorative Laminates Industry (ICDLI)
  3. 3Formaldehyde Emission Standards for Composite Wood Products (TSCA Title VI) — U.S. Environmental Protection Agency (EPA)
  4. 4Pre-Construction Subterranean Termite Control — North Carolina Department of Agriculture — Structural Pest Control
  5. 5Termites: How to Identify and Control Them — U.S. Environmental Protection Agency (EPA)
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This guide is for general information and planning, based on standards and technical guides. Standards are revised periodically; in Saudi Arabia the binding reference is the Saudi Building Code and the instructions of the competent authorities. For design and execution, use a licensed engineer or technician. Found an error? Tell us.