Three materials, three answers. Cedar at ~$3-4/LF lasts 15-20 years stained + maintained, takes face-screws, looks the part for visible decks. Pressure-treated at ~$1.50-2/LF lasts 10-15 years before the surface checks, takes face-screws, wins on budget for utility decks. Composite (Trex / TimberTech / AZEK) at ~$3-7/LF lasts 25-30 years per warranty, requires hidden clips, earns its keep on shaded north-facing decks where wood rots fast.
The structural frame underneath is the same regardless — 2×8 or 2×10 PT joists at 16″ on center per AWC DCA-6, post-and-beam ledger flashed against the rim joist, footings below frost line. Run the surface materials through the deck cost calculator (surface-only — the frame goes through your contractor + the AWC DCA-6 prescriptive guide).
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Quick answers about SiteworkMath's calculators and material take-offs — concrete yardage, topsoil + mulch volume, tile box-count, deck-surface materials. Free, no signup. Not structural-engineering or code advice — for joist / beam / footing / permit decisions, talk to a structural engineer, licensed contractor, or your local building department.
Hi, I'm the SiteworkMath assistant. I answer questions about the calculators and guides on this site — concrete yardage, topsoil, mulch, tile, and decking material math. I'm not a structural engineer or a licensed contractor; I'm a calculator built around the math that James Wu — Chicago-area flipper — uses on his own jobs. For structural decisions (joist sizing, beam spans, footing depth in your soil + climate, anything that needs a permit) talk to a licensed structural engineer or your local building department.
How pros actually do this
The cedar deck I built at the Chicago-suburb gut rehab in summer 2020 was a 16×12 ft surface — clean rectangle, west-facing for afternoon sun, parallel-to-house layout, 5.5″ cedar boards, 16 ft lengths, 27 board rows × 16 ft = 432 LF exact, 30 boards ordered with the 10% cushion. The deck stained to a soft warm amber by the open house, photographed great, and held up clean through the showing window. Cedar was the right pick because (a) it was a visible surface from the kitchen, (b) west-facing dries fast so rot risk was low, and (c) the budget couldn't carry composite on a flip with eight other line items competing.
The PT-vs-cedar split decision is where most of the cost discipline lives. PT runs roughly half the per-LF cost of cedar and lasts about 70% as long — so the break-even on visible decks is roughly “does this owner stain it?” If the answer is yes, cedar wins on appearance + the lifespan gap closes; if the answer is no, PT wins on cost and ages similarly (both go gray + check; cedar just does it slower). For utility decks (under a workshop, behind a garage, somewhere a neighbor doesn't see) PT is almost always the right answer regardless of stain-and-seal habits.
Composite is the last 20% of the curve. It's 50-100% more expensive on materials, requires the hidden-clip system for warranty, and demands flatter joist work because the boards have less give than wood does — 12″ on center isn't unusual on composite installs vs the 16″ standard on wood. The warranty conditions are real, not optional: face-screwing Trex into a deck looks fine for two seasons and then voids when the boards start flexing past spec. If you're paying composite money, follow the manufacturer install guide to the letter — that's the warranty discipline that separates trust-credible installers from the “close enough” ones.
The decision matrix
Six rows, three columns. Read across the row to see how the three materials trade off on that dimension; pick the column that wins on the dimensions that matter to your job.
| Dimension | Cedar | Pressure-treated | Composite |
|---|---|---|---|
| Cost (per LF) | $3-4 | $1.50-2 | $3-7+ |
| Lifespan | 15-20 yr (stained) | 10-15 yr | 25-30 yr (warranty) |
| Fastener | Face-screws (clips optional) | Face-screws (clips optional) | Hidden clips (required for warranty) |
| Maintenance | Annual stain + seal | Stain optional, recheck 3-5 yr | Wash with soap; no stain |
| Install difficulty | Standard; pre-drill ends | Standard; hand-select boards | Slower; clip system + flatter joists |
| When to pick | Visible deck, owner stains | Utility deck, budget tight | North-facing, low-maintenance |
Run the surface math yourself
Plug in your deck dimensions and pick a material. The calculator's material preset auto-fills the fastener type (face-screws for cedar / PT, hidden clips for composite per warranty); plug in your local price-per-LF for the cost output. Surface-only — the frame stays out of scope.
Surface-material only
This calculator estimates deck boards + fasteners + (optional) material cost. It does NOT estimate joists, beams, posts, footings, ledger flashing, railings, stairs, permits, labor, or structural-design review. Frame must be designed per AWC DCA-6 + IRC 2021 R5 by a qualified contractor or engineer.
Where this number breaks down
A few traps that put the material decision on the wrong side:
- Composite warranty void on face-screws.Trex / TimberTech / AZEK warranties require hidden-clip systems — face-screwing the boards looks fine for two seasons and then voids the warranty in writing when the boards flex past spec. If you're paying composite money, follow the manufacturer install guide to the letter.
- 20 ft boards warp regardless of material. SiteworkMath field preference caps practical residential board length at 16 ft. Composite is no exception — premium AZEK 20 ft boards still cup under wet service. AWC DCA-6 covers structural framing (joist spans, ledger, beam, footings); it doesn't publish board-length max — the 16 ft cap is operator + manufacturer-handling experience. Plan staggered runs across 12-16 ft boards instead of single-piece spans.
- PT ships wet + variable.Pressure-treated ships saturated; a 16 ft board can vary 1/4″ in straightness from rack to rack. Hand-select at the lumber yard. The calculator assumes uniform stock; the field doesn't. Add an extra 5% to the waste cushion if your supplier's PT stock is rough.
- Cedar at the cut ends rots first.Cedar's rot resistance lives in the heartwood. Cut ends expose the sapwood, which rots fast in wet contact. Seal cut ends with end-grain sealant before installation; otherwise plan to replace 2-3 boards per deck within 5-7 years.
- Joist spacing isn't universal. 16″ on center is residential code default. Composite manufacturers often require 12″ on center for diagonal layouts or heavier loads. Confirm the manufacturer install spec before the joist work goes in — re-spacing joists after the fact is a tear-out.
Frequently asked
What's the cheapest deck material?
Pressure-treated wins on upfront cost — typically $1.50-2 per linear foot for 5/4×6 deck boards versus $3-4/LF for cedar and $3-7/LF for composite (Trex, TimberTech, AZEK premium tiers can run higher). On a 16×12 ft deck (480 LF of decking), PT runs ~$720-960 in materials, cedar ~$1,440-1,920, composite ~$1,440-3,360. PT is the cheapest answer for under-deck workshops + utility decks where you're not chasing a finished look.
Which deck material lasts longest?
Composite, by a wide margin — Trex / TimberTech / AZEK ship with 25-30 year warranties on the surface boards (warranty conditions require their hidden-clip fastener systems and proper joist spacing per the manufacturer install guide). Cedar lasts 15-20 years stained + maintained. Pressure-treated lasts 10-15 years before the surface starts checking + cracking. North-facing or shaded decks where wood rots fast are where composite earns its keep; sunny dry decks see cedar age gracefully for closer to 20 years.
Do I need hidden clips for cedar or PT?
No — cedar and PT take face-screws as standard. Hidden clips are an optional upgrade for the cleaner look (no visible screw heads) and run roughly $80-150 extra per 100 sq ft of deck. For composite (Trex, TimberTech, AZEK), hidden clips are required for warranty — face-screws void the warranty even though the deck performs identically the first few seasons. The fastener-type decision is material-driven for composite, aesthetic-driven for wood.
Cedar or composite for a north-facing deck in Chicago?
Composite. North-facing decks in Chicago see less sun + more sustained moisture; cedar holds up but needs annual stain-and-seal maintenance to avoid mildew + rot at the cut ends. Composite ignores the orientation entirely. The cost premium (~50-100% on materials) pays back over 15-20 years where cedar would need replacement boards every 3-5 years. South-facing decks in Chicago tip the math the other way — cedar dries fast, ages well, and the maintenance is minor.
Can I mix materials — composite surface on PT joists?
Yes — and it's the most common residential setup. PT 2×8 or 2×10 joists carry the structural load (cheap + treated against rot from ground contact), composite 5/4×6 boards on top carry the visible surface (rot-resistant + low-maintenance). Confirm the joist-spacing requirements from the composite manufacturer's install guide — Trex typically wants 16″ on center for residential, 12″ for diagonal layouts and heavier loads. The frame goes through AWC DCA-6 + IRC 2021 R5 regardless of surface material.
Is there a deck material I should avoid?
Old-spec PT (CCA, pre-2003) — but you can't buy it new anyway. Modern PT (ACQ or copper-azole treated, 2003+) is fine for residential use. The other category to avoid: "value" composite from non-major brands. Cheap composite cracks + fades faster than name-brand Trex / TimberTech / AZEK and the warranties are weaker. If you're spending composite money, spend it on a brand whose warranty is enforceable. Cedar is fine; ipé and other tropical hardwoods are gorgeous but $8-12/LF and require pre-drilling every fastener.
Related guides
- Deck board spacing + joist layout →
- Deck cost calculator (cluster anchor) →
- Concrete yardage (footings live here) →
- Tile calculator (sister cluster) →
Once the material decision is made, the next decision is joist spacing + board-end alignment for staggered patterns. Composite warranty often demands 12″ oc; cedar + PT take 16″ oc as residential default. Deck board spacing and joist layout covers it.
By James Wu. Material per-LF pricing reflects typical Chicago-suburb supplier ranges as of 2026; verify against your local lumber yard or supplier quote. Joist-spacing default (16″ on center) + structural-frame opt-out come from American Wood Council DCA-6 — Prescriptive Residential Wood Deck Construction Guide; the 16 ft practical board-length cap is SiteworkMath field preference, not a DCA-6 publication. Composite warranty conditions follow Trex installation guidance and TimberTech installation guidance; AZEK has equivalent published install + warranty docs. IRC 2021 Chapter 5 (Floors) is paywalled at ICC and cited by name. Engine logic in lib/sitework/deck.ts. Surface- material discussion only — frame design (joists, beams, posts, footings, ledger flashing, railings, stairs) requires AWC DCA-6 + IRC 2021 R5 + a qualified contractor or engineer. Not structural-engineering advice. Full methodology.