Douglas Fir vs Redwood: Which Is Better for a Deck?
Douglas fir is denser and about 620 lbf on the Janka scale, making it stronger and cheaper than redwood’s 450 lbf average — but redwood’s heartwood resists decay and insects on its own, without pressure treatment. Pick the wrong one and a deck either flexes under load or rots at the ground-contact points within a few years. This guide compares hardness, decay resistance, cost, and the best use for framing, decking, and painted porch steps.
Quick Answer
Use Douglas fir for framing, beams, and load-bearing structures where strength-per-dollar matters most. Use redwood (a durable heartwood grade like Construction Heart) for decking, fence posts, and anything touching soil or moisture, since its heartwood resists rot without chemical treatment. Douglas fir needs a preservative or pressure treatment outdoors; redwood generally doesn’t.
📊 Douglas fir averages 620 lbf on the Janka hardness scale versus 450 lbf for redwood (480 lbf old-growth, 420 lbf second-growth) — Source: The Wood Database, Douglas Fir & Coast Redwood species profiles
Douglas Fir vs Redwood: Full Property Comparison
Both are prized North American softwoods, but they come from different families and are graded differently — Douglas fir for structural strength, redwood for natural durability and appearance. The table below compares the properties that actually decide which one to use.
| Property | Douglas Fir | Redwood |
|---|---|---|
| Janka hardness | 620 lbf | 450 lbf avg (480 old-growth / 420 second-growth) |
| Density | 32 lbs/ft³ | 26 lbs/ft³ avg |
| Decay resistance (heartwood) | Moderately durable; susceptible to insects | Moderately to very durable; naturally insect-repellent |
| Grain/appearance | Light brown, straight grain, visible growth rings | Reddish-brown, finer and smoother grain |
| Typical cost | Roughly 50% cheaper than redwood | Premium price; $3,000–$6,000 more on a typical 14×22 deck |
| Best use | Framing, beams, trusses, structural work | Decking, fencing, siding, anything near soil/moisture |
Which Wood Is Stronger and Harder?
Janka hardness is a lumber-industry test that measures the force needed to embed a 0.444-inch steel ball halfway into a wood sample — the higher the number, the more resistant the wood is to dents and wear. Douglas fir’s 620 lbf rating comes largely from its tight growth rings and density (32 lbs/ft³), which also gives it a higher modulus of rupture than redwood. That extra density is why Douglas fir is the default choice for joists, beams, and load-bearing framing.
Redwood is noticeably softer at 450 lbf average, and old-growth redwood (480 lbf) is measurably harder than the second-growth redwood (420 lbf) sold at most lumberyards today — most new redwood lumber is second-growth. That softness isn’t a defect; it makes redwood easier to cut and nail by hand, and it’s part of why the wood is stable and resists warping across humidity swings.
Which Wood Resists Decay and Insects Better?
Heartwood is the dense, inner wood of a tree; it’s the part that carries natural decay resistance in both species — the outer sapwood of either wood has almost none. Redwood’s heartwood gets its resistance from fungicidal tannins that discourage decay fungi, while Douglas fir heartwood is rated moderately durable by the USDA but is more vulnerable to insect attack. Redwood is generally sold in graded heartwood lots (Construction Heart, Deck Heart) specifically for ground-contact and outdoor use, while Douglas fir almost always needs a borate or copper-based preservative before it goes outside.
“Douglas-Fir heartwood is rated to be moderately durable in regard to decay, but is susceptible to insect attack.”
Does Redwood’s Rot Resistance Ever Wear Out?
Yes. The tannins that protect redwood heartwood are water-soluble, so they slowly leach out with repeated rain and moisture exposure over years, and older, weathered redwood does become more vulnerable over time. Neither species is rot-proof in standing water or buried, wet contact — for true ground-contact posts, pressure-treated lumber still outperforms both untreated Douglas fir and untreated redwood. See our guide on whether Douglas fir is truly rot-resistant for the full USDA durability breakdown.
Douglas Fir vs Redwood: Which Is Better for a Deck?
For a deck, redwood is usually the better pick if budget allows — its heartwood resists rot and insects without chemical treatment, so it holds up to ground-level moisture and splash-back from the yard better than untreated Douglas fir. Douglas fir works for a deck too, but only if it’s pressure-treated or sealed with a penetrating preservative, and it should be reserved for the structural framing (joists, beams) underneath rather than the exposed decking boards.
A common approach on this site’s reader projects: frame the deck substructure in pressure-treated or preservative-sealed Douglas fir for strength and cost savings, then use redwood heartwood boards for the visible decking surface where rot resistance and appearance matter most. If redwood’s premium price is the deciding factor, treated Douglas fir with an annual sealant reapplication is the budget alternative.
Best Deck Sealer Pick
Ready Seal Exterior Wood Stain & Sealer, 1 Gallon – $40.98
A penetrating oil sealer for exactly the situation this guide covers: sealing untreated Douglas fir framing or redwood decking against the moisture that causes tannin leaching and rot over time.
- Best for: new or bare deck boards on either species before the first season of weather exposure
- Why we picked it: penetrates instead of forming a surface film, so it won’t peel like a film-forming stain can on redwood’s tighter grain
- Main drawback: needs reapplication every 1–3 years depending on sun exposure
Compare more Douglas fir & redwood project supplies
 Option 1 Wolman WOODLIFE CopperCoat Wood Preservative, Quart – $21.75
|
 Option 2 304 Stainless Steel Deck Screws, 500-Pack – $56.99
|
 Option 3 Klein Tools ET140 Pinless Moisture Meter – $49.97
|
As an Amazon Associate we earn from qualifying purchases.
What About Painted Porch Steps?
For painted porch steps, Douglas fir is the more common choice because its tighter, straighter grain holds paint film more evenly than redwood’s softer, more porous grain, which can telegraph through paint over time. Prime bare Douglas fir with an oil-based or stain-blocking primer first, since fir’s resin pockets can bleed through paint if left unsealed. Redwood can be painted too, but it’s more often left with a clear sealer or semi-transparent stain specifically to show off its natural color.
Cost Comparison: Which Wood Costs Less?
Douglas fir is roughly 50% cheaper than redwood at most lumberyards, and that gap compounds fast on a full project — a typical 14×22-foot deck built in redwood instead of Douglas fir runs about $3,000 to $6,000 more in material cost alone. That premium buys redwood’s natural decay resistance and finer grain, but it isn’t a small difference once a project scales past a small repair or a single set of steps. For a full breakdown of current per-square-foot pricing, see our redwood deck lumber prices guide.
Douglas fir and redwood aren’t the only comparison worth checking before you buy — if cedar is also on your shortlist, our Douglas fir vs cedar guide and cedar vs redwood cost comparison cover how cedar stacks up on price and rot resistance against both woods here. For framing specifically, see how Douglas fir compares to southern yellow pine on strength.
Frequently Asked Questions
Which is better for a deck, Douglas fir or redwood?
Redwood is generally better for exposed decking because its heartwood resists rot and insects without treatment. Douglas fir works for the deck’s structural framing underneath, but the boards you walk on should be redwood heartwood or pressure-treated fir.
Is Douglas fir stronger than redwood?
Yes. Douglas fir is denser (32 lbs/ft³ vs 26 lbs/ft³) and harder (620 lbf vs 450 lbf on the Janka scale), which is why it’s the standard choice for beams, joists, and other load-bearing framing rather than redwood.
Does redwood or Douglas fir resist rot better?
Redwood heartwood resists rot better without any chemical treatment, thanks to natural tannins. Douglas fir heartwood is only moderately durable and is more vulnerable to insects, so it typically needs a preservative or pressure treatment for outdoor use.
Is Douglas fir cheaper than redwood?
Yes, Douglas fir typically costs about half as much as redwood. On a mid-size deck project, choosing redwood over Douglas fir can add $3,000 to $6,000 to the material cost.
Can you use Douglas fir for outdoor porch steps?
Yes, but it should be pressure-treated or sealed with a preservative first, then primed and painted. Douglas fir’s straight, tight grain actually holds paint more evenly than redwood, which is why it’s a common choice for painted porch steps specifically.
What’s the visual difference between Douglas fir and redwood?
Douglas fir is light brown with a straight, prominent grain pattern and visible growth rings. Redwood is reddish-brown with a finer, smoother grain that’s less pronounced. Most people can tell them apart at a glance once they know the color difference to look for.
Which Wood Should You Choose?
Choose Douglas fir when strength-per-dollar matters most — framing, beams, and structural work where the wood will be covered, protected, or pressure-treated. Choose redwood when the wood will be exposed to weather and you want to skip the maintenance cycle of chemical treatment — decking, fencing, siding, and porch posts near ground contact. Many projects, including most decks, end up using both: Douglas fir framing underneath, redwood boards on top.
