Pressure-treated wood or composite: how to choose

Pressure-treated wood

An economical choice for exterior structure when rated for the actual use: above ground, ground contact or freshwater. It can split, warp, shrink and need stain or sealer. Exposed cuts and holes must be treated per manufacturer.

Composite

Mostly used for decking surfaces and trim, not automatically as structure. It resists rot and reduces maintenance, but may cost more, heat in sun, expand and require system-specific spacing, ventilation, gaps and fasteners.

Choice by location

• Hidden structure: properly rated treated wood or an engineered system.
• High-sun surface: check composite temperature and colour.
• Damp, poorly ventilated area: drainage details are paramount.
• Stairs and rails: verify stiffness, slip and approvals.
• Near a pool: barefoot grip, heat and chemical resistance.

Fasteners and compatibility

Use corrosion-resistant fasteners compatible with the treatment and environment. Do not randomly mix aluminum, galvanized steel, stainless steel and chemicals. Follow manufacturer details for clips, screws, plugs, joists, protective tape and ventilation.

True cost

Compare purchase, delivery, substructure, hardware, waste, initial finish, 15–25 years of maintenance, repairability and appearance. Premium composite can be worthwhile when maintenance time is valued; wood remains easy to modify and repair.