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Rebuild a Deck: Project Walkthrough
Published July 19, 2026
The 5 calculators for this job, in order
Run them in this sequence — each step's measurements feed the next, and changing an early number changes every number after it.
Rebuilding a deck starts with information a brand-new deck never has: the old frame. Before anything comes down, it's worth reading what years of weather and load have already told you — where the ledger shows staining, where a joist has sagged, whether the old footings are actually at the depth and diameter they should be. A rebuild that skips this and just copies the old layout onto new lumber repeats whatever the old deck got wrong, footings included.
The build order: assess and tear off, size new footings from the layout you actually want (not the layout that happens to already be there), frame to the span those footings were sized for, then deck and fasten. That's the deck footing calculator, floor joist calculator, deck board calculator, and deck screw calculator, with the dumpster size calculator handling the teardown at the front of the job. This is structural, load-bearing work — treat every number here as a planning estimate, confirm depth and sizing against your local code, and get a professional or engineer's sign-off for anything beyond a small, low platform.
1. Read the old frame before you touch a pry bar
Check the old footings first, if you can expose them: diameter, depth relative to your local frost line, and any cracking or heaving. An old deck built to a lighter, older code, or built without a permit at all, often has undersized footings that happened to hold up under a smaller original design — evidence that the deck stayed standing, not evidence that the footings were sized correctly. Check the ledger connection to the house next, since a rebuild is a chance to fix a ledger that was only ever a handful of lag screws into siding, which is exactly the kind of connection failure that shows up in deck-collapse reports.
Note anything you want to change about the layout at this stage — a post moved to open up a walkway, a wider bay to fit new furniture, boards run a different direction — because the next two steps size everything off whatever layout you settle on here, not off the deck that's currently standing.
2. Tear off and size the container on real demo weight
Run the dumpster size calculator using the actual old decking and framing lumber coming out, plus any old concrete you're breaking out of footings that aren't being reused — old deck lumber that's been pressure-treated for two decades is heavier than the equivalent length of new stock, since it's absorbed moisture over its life outdoors. See estimating demolition debris for converting a deck's square footage and board count into the volume and weight figures the calculator wants.
Leave existing footings in place wherever the new layout reuses that exact post position and the old footing checked out in step 1 — breaking out sound concrete for no reason adds debris and labor for nothing.
3. Size footings from the new post layout, not the old one
Run the deck footing calculator using the post spacing and joist span the new layout actually calls for, along with your soil's bearing capacity — a presumptive figure for your soil type if you don't have a geotechnical report, checked against what your local building department accepts. This is the step where the layout choice from step 1 stops being a sketch and starts being a concrete order, and it's also the step with the clearest example on this entire site of an early decision changing a later number, worked through in detail below.
How two feet of post spacing turns a 16-inch footing into a 20-inch one
A deck's footing diameter is sized from the tributary area each post actually carries — roughly the post spacing along the beam multiplied by half the joist span, since half of that span lands on the beam and the other half lands on the ledger. Take a common case: a 12-foot joist span, posts originally spaced 6 feet apart along an 18-foot beam (three even bays), a combined live and dead load of 50 pounds per square foot, and soil rated for 1,500 pounds per square foot. That tributary area works out to 36 square feet per post, a load of 1,800 pounds, and a required footing diameter that lands just under 15 inches — which rounds up to the next standard size the footing calculator offers, 16 inches.
Now say the layout gets tidied during the redesign in step 1 — a post moved out to line up with a paver edge and dodge a tree root, widening that one bay from 6 feet to 8 feet while everything else stays the same. Tributary area for that post jumps to 48 square feet, load to 2,400 pounds, and the required diameter to just over 17 inches — which rounds up past 16 straight to the next standard size, 20 inches. A two-foot layout tweak made for tidiness, decided before anyone thought about footings, pushes one post's footing up a full standard size, meaning meaningfully more concrete and a bigger hole for that post alone. This is why the footing calculator has to run after the layout is actually finalized, not before — and why every post along an uneven bay spacing is worth checking individually rather than sizing the whole deck off the smallest or most convenient bay.
4. Frame to the span the footings were actually sized for
Run the floor joist calculator using the same span and spacing values that went into the footing sizing in step 3 — not a round number that looked close enough. If the footing calculator was run at a 12-foot joist span and 8-foot post spacing, the framing has to actually deliver that same span and spacing, since the footing's diameter was sized specifically for the load those numbers produce, and a longer span or wider post spacing than what was calculated pushes more weight onto a footing that wasn't sized to carry it.
5. Decking direction decides joist spacing, and joist spacing decides screw count
Board direction has to be settled before final joist layout, not after: composite decking commonly needs tighter joist spacing than solid wood of a similar thickness to avoid visible deflection underfoot, and a diagonal decking pattern effectively shortens each board's unsupported span between joists compared to running boards straight across, which can also call for tighter spacing. Run the deck board calculator once the joist layout is locked in, using the gap spec for your chosen board material.
Once decking is planned, run the deck screw calculator off the actual joist count and spacing from step 4, not off square footage alone — the number of fastening points per board is set by how many joists that board actually crosses, and a tighter joist spacing means more fasteners per board even though the board count itself hasn't changed.
What goes wrong when footings get poured before the layout is final
Pour footings sized off a first-draft layout, then decide during framing that a post really does need to move for clearance or symmetry, and there's no fixing it without breaking out cured concrete — a footing is the one part of a deck rebuild that's genuinely permanent the moment it's poured. The layout decisions in step 1, however minor they feel, need to be the final ones before step 3's footing calculation runs, not decisions still being worked out while concrete trucks are already scheduled.
The same ordering problem shows up between framing and decking: order deck boards off square footage alone before joist spacing and direction are locked in, and a later decision to switch to composite or to run boards diagonally can leave you with boards that don't reach cleanly between the joists you already built, or a fastener count that no longer matches the frame underneath it.
FAQ
Do I need a new permit for a deck rebuild if the footprint isn't changing?
In most jurisdictions, yes — a rebuild that replaces the structural framing is generally treated the same as new construction for permitting purposes, even if the finished deck looks identical to what was there before, and an unchanged footprint on its own is not typically grounds for an exemption.
Can I reuse old joist hangers and post bases if they still look solid?
It's generally not worth it — hardware rated for older lumber treatments can corrode faster in contact with modern pressure-treated wood's different chemical formulation, and hangers that have been through repeated wet-dry cycles for years may have lost strength in ways that aren't visible from a surface inspection, so new connectors matched to your current lumber are the safer call on a rebuild.
How do I know if my old footings are actually deep enough, or if I'm just assuming they are because the deck never moved?
A deck standing without visible problems for years is evidence the footings survived that specific load and soil condition, not evidence they meet current depth requirements — dig down to expose at least one footing fully and measure it against your local frost line before deciding to reuse any of them.
Is it worth upgrading from wood to composite decking during a rebuild, given the framing implications?
It can be, but decide before finalizing joist spacing in step 4, not after the frame is built — composite's stricter span ratings sometimes call for tighter joist spacing than a wood-appropriate frame provides, and sistering additional joists into an already-built frame to meet a composite product's span rating is considerably more work than spacing correctly the first time.
What's the actual risk of just eyeballing post spacing to make the layout look tidy, rather than running the numbers?
Post spacing directly sets how much of the deck's total load lands on each footing, so widening a bay to avoid a step in the yard or to line posts up with a fence changes that footing's required size — sometimes by a full standard size increment — which is exactly the kind of change that's invisible until you actually run the footing calculator with the new spacing.