Which wood is best for a deck in Southern California: redwood, cedar, ipe or thermally modified?

Heartwood is the whole story with redwood and cedar

Redwood and western red cedar earn their reputation from their heartwood, the dense inner wood that carries natural extractives insects and fungi dislike. The pale sapwood near the bark has none of that protection and rots about as fast as any softwood. So the grade matters more than the species name. For decking you want an all-heart grade; for redwood that is Construction Heart or better, and the clear heart grades are beautiful but priced accordingly and often not necessary for a deck surface.

Both woods are soft. Chairs scraped across them leave marks, dogs' nails show, and a dropped grill tool dents the board. They are also light, stable and a pleasure to work, which means tight joints and clean miters. Redwood is the stronger of the two and has long been the default in California; cedar is more common up the coast but readily available here.

Ipe and the dense tropical hardwoods

Ipe, cumaru, garapa and their relatives are so dense that they barely absorb water, resist insects and fire better than most softwoods, and can last decades with almost no attention. Left alone, ipe weathers to an even silver gray; oiled once a year or so, it stays a rich brown. Nothing else feels as solid underfoot.

The tradeoffs are in the building and the buying. Every hole must be pre-drilled, blades dull fast, and the boards are heavy enough that the framing and the crew both feel it. Hidden-fastener systems designed for hardwood exist and work well. On sourcing, we insist on wood with credible chain-of-custody certification, and we will tell you if the lead time or the certification is in doubt. If you do not want to think about where the wood came from, this is not the material for you.

Thermally modified wood

Thermal modification bakes a plentiful species such as ash, pine or poplar at high temperature in a low-oxygen kiln. The heat changes the wood's sugars so fungi have less to eat and the cells take on much less water, which makes the boards far more stable and rot-resistant than the raw species, with no chemical treatment. The color is a deep, even brown that grays in the sun like any wood.

The process also makes the wood somewhat more brittle and reduces its strength, so it is a decking and cladding material rather than a framing material, and the manufacturer's span and fastener guidance should be followed exactly. It is an interesting middle path for a client who wants real wood, wants it domestic and chemical-free, and will accept a newer product with a shorter track record than redwood or ipe.

Pressure-treated decking, for completeness

Pressure-treated pine or fir decking is the economy option and it has a place on utility decks and in places where appearance matters little. In our climate it tends to check, twist and splinter as it dries, and it needs a finish to look like anything. Current treatments are copper-based and corrosive to ordinary steel, so hot-dip galvanized or stainless fasteners are required. Older decks may still carry CCA-treated wood, which the EPA phased out of residential use in the early 2000s; it is safe to leave in place but should not be burned or sanded without care.

How we choose with a client

There is no wrong answer here, only a wrong match between the wood and the household. We bring samples and let you drag a chair across them.

• Barefoot feel and heat: redwood and cedar stay coolest; ipe gets warm; dark thermally modified boards warm as well.
• Maintenance appetite: ipe tolerates neglect best; redwood and cedar want a finish refreshed regularly to keep color.
• Wear: ipe shrugs off furniture and dogs; redwood and cedar show it.
• Fire zones: dense hardwoods and some treated products meet ignition-resistance standards; untreated softwoods generally do not. We check the listing for your address.
• Sourcing: redwood and thermally modified domestic species are the simplest to source responsibly; tropical hardwoods require certification you can verify.

Related questions

Sources and further reading