Project planner
Deck Framing: Joist, Beam, Post & Footing Planner
Competition on this search is the lowest of anything we measured at this volume, because nobody has built the tool. The span tables exist and are public — this applies them to your deck.
- Joist size for your span, spacing and species
- The full span table, so you can check the choice
- Beam size and the post spacing it allows
- Footing diameter from tributary load and soil bearing
- Footing depth against your frost line
- Guard, railing and permit thresholds flagged
Deck Framing: Joist, Beam, Post & Footing Planner — interactive tool
Deck dimensions
The distance joists cross unsupported — house to beam, or beam to beam.
Above about 30 in, guards and a permit come into play.
Ledger failure is the leading cause of deck collapse. Freestanding avoids the connection entirely.
Site conditions
Set by your building department. Footings must go below it or they will heave.
1,500 is the conservative default for unknown soil.
12 × 16 ft · Southern pine · 16" o.c.
Your framing schedule
joists at 16 in centres — rated to span 14 ft
- Joists
- 13 × 12 ft
- Beam
- (2) 2×12
- Footings
- 3 × 18"
These are prescriptive sizes from published residential deck span tables at the standard 40 psf live plus 10 psf dead load, chosen at the conservative end. They are a sound starting point for a permit application and a conversation with your building department — not a substitute for either.
Now plan the boards on topHome & Garden Living · homeandgarden.living/tools/deck-framing-planner
These are prescriptive sizes, not an engineered design
The spans here are the conservative end of published residential deck tables at 40 psf live plus 10 psf dead load, for No. 2 grade timber. They do not account for your local snow load, unusual geometry, hot tubs, roof structures, or anything cantilevered beyond the normal allowance. Your building department will have its own requirements and may want a stamped design. Where they differ from this, they win.
The ledger connection is where decks kill people
Ledger failure is the leading cause of catastrophic deck collapse, and it fails suddenly and completely rather than gradually. The ledger must be fastened into the house's rim joist or framing with structural fasteners at the specified spacing — never into sheathing, never into brick veneer, and never with lag screws where the code calls for through-bolts. It must be flashed above so water cannot get behind it, because a rotted rim joist behind an intact-looking ledger is the classic failure. If you cannot positively identify what is behind the cladding, this connection is worth a professional regardless of your confidence with the rest.
This deck almost certainly needs a permit and inspections
Attached decks, raised decks and anything over about 200 square feet trigger permit requirements nearly everywhere. Inspections typically happen at footings (before concrete), framing (before decking), and final. Building without one risks an order to remove the deck, and it will surface during a sale.
Use fasteners rated for treated timber
Modern pressure-treated lumber is corrosive to standard steel. Every fastener, joist hanger, post base and structural screw in contact with it must be hot-dip galvanised or stainless. Mixing electroplated fasteners into treated lumber produces connections that fail quietly over a few seasons.
Material schedule
| Item | Quantity | Note |
|---|---|---|
| 2×10 joists | 13 at 12 ft | Southern pine, No. 2 or better |
| (2) 2×12 built-up beam | 16 ft | Laminated with structural fasteners, not nails alone |
| 6×6 posts | 3 | On standoff post bases — never set directly into concrete |
| Concrete footings | 3 at 18 in dia × 42 in deep | About 31 bags of 60 lb mix |
| Joist hangers | 13 | Galvanised or stainless, sized to the joist |
| Ledger board | 16 ft of 2×10 | With flashing above and structural fasteners at code spacing |
Joist span table — Southern pine, No. 2 grade
| Joist | 12" o.c. | 16" o.c. | 24" o.c. |
|---|---|---|---|
| 2×6 | 9.9 ft | 9 ft | 7.6 ft |
| 2×8 | 13.1 ft | 11.9 ft | 9.7 ft |
| 2×10yours | 16.2 ft | 14 ft | 11.5 ft |
| 2×12 | 18 ft | 16.6 ft | 13.6 ft |
Conservative values at 40 psf live + 10 psf dead. Hot tubs, roof structures and heavy snow all exceed this and need a designed solution.
- Tributary load per post
- 2,460 lb
- Footing area needed
- 1.64 sq ft
- Footing depth
- 42 in
- Concrete
- 31 bags
Take these numbers further
What this estimate assumes
- · Design load is 40 psf live plus 10 psf dead — the standard residential deck load. Hot tubs, planters, roof structures and heavy snow all exceed it and need a designed solution.
- · Span figures are the conservative end of published prescriptive tables for No. 2 grade timber. Higher grades span further; this deliberately does not assume them.
- · Footing size is derived from tributary area × 50 psf against 1500 psf soil bearing. Soil capacity varies enormously and a local test beats any default.
- · Footing depth is frost depth plus 6 in, with a 36 in minimum. Your building department sets local frost depth.
- · Concrete is estimated at 0.6 cu ft per 60 lb bag, with no allowance for over-excavation or spillage.
- · This sizes members prescriptively. It is not a stamped engineering design and does not claim to be one.
Prescriptive sizing from published span tables. Not a stamped engineering design, and your building department has the final word.
Decking is the part people photograph and the part every calculator addresses. The frame underneath is the part that decides whether the deck is safe, and it is governed by published span tables that are freely available and almost never applied to a specific deck by anything you can find online.
Those tables are not complicated to use. A joist of a given size, in a given species, at a given spacing, spans a stated distance under the standard residential deck load of 40 psf live plus 10 psf dead. Beams follow from post spacing, footings follow from tributary load and soil bearing, and footing depth follows from your local frost line. Every one of those is arithmetic once you know the inputs.
This applies them at the conservative end, deliberately. An oversized joist costs a few dollars more per length. An undersized one produces a deck that feels springy on day one, sags within a few years, and fails under the load of a party — which is when decks are fullest and when failures make the news.
The ledger is where decks kill people
If your deck is attached to the house, one connection carries a large share of the whole structure's load, and it is the connection that fails in almost every catastrophic deck collapse. It is worth understanding before anything else.
The ledger is the board bolted to the house that the joists hang from. It must fasten into the house's rim joist or framing — structural timber — with fasteners of the specified type at the specified spacing. It must not be fastened to sheathing, which is not structural. It must not be fastened to brick veneer, which is not structural either. And lag screws are not always an acceptable substitute for through-bolts; the code is specific about this and the specification varies with the situation.
Then there is water. A ledger fixed flat against a wall without flashing above it creates a permanent horizontal ledge holding water against the house. The rim joist behind it rots slowly and invisibly, and the ledger stays looking perfectly sound while the timber it is bolted to turns soft. Decks have collapsed years after construction for exactly this reason, with no external warning at all.
Failures here are sudden and total rather than gradual. If you are building this yourself and cannot positively identify what is behind the cladding, this one connection justifies a professional even if you do the rest. A freestanding deck avoids the problem entirely at the cost of two more posts, and on a lot of projects that is the better trade.
How the sizing chain works
The chain runs downward. Joists span from the house or a beam to another beam, and their size follows from that span, the spacing between them, and the species of timber. Closer spacing lets a smaller joist span the same distance, which is why 12-inch centres often let you drop a size.
Beams carry the joists, and a beam's allowable span between posts depends on how much deck it is carrying — the tributary width, which is roughly half the joist span. A beam supporting 12-foot joists carries twice the load of one supporting 6-foot joists over the same length, so it either gets larger or the posts get closer.
Posts carry the beam down to footings, and footings spread that load into the ground. Footing size comes from the load on the post divided by the soil's bearing capacity: 1,500 psf is the conservative default for unknown soil, and firmer ground allows smaller footings. Footing depth is set by frost, not by load — a footing that stops above the frost line will be lifted every winter, and a deck that heaves will rack, pull at the ledger, and eventually tear itself apart.
- Closer joist spacing lets a smaller joist span the same distance. It is often cheaper than the next size up.
- Diagonal decking increases the effective span by about 41% and needs joists at 12 inches on centre.
- Every fastener, hanger and post base in contact with treated timber must be hot-dip galvanised or stainless. Standard steel corrodes fast in modern treatment chemistry.
- Posts sit on standoff bases above the concrete, never embedded in it. Buried posts rot from the inside where nobody can see.
Height changes everything at 30 inches
Around 30 inches above grade — the exact figure varies by jurisdiction — a deck crosses a threshold that changes its requirements substantially. Guards become mandatory, typically at least 36 inches high with balusters spaced so a 4-inch sphere cannot pass between them.
The important part of the guard requirement is not the height but the loading. A guard must resist a 200-pound concentrated load applied in any direction at the top rail. That is a structural requirement and it is where most site-built guards fail: notching a post to fit around a rim joist removes most of its strength at precisely the point where the bending load is highest. Purpose-made tension ties exist for this connection and are worth using.
A raised deck also needs larger footings and taller posts, and above about 6 feet, bracing to resist racking. All of this is in the prescriptive tables, and all of it is why a raised deck costs considerably more per square foot than a ground-level one.
Permits, inspections and why they are worth having
Attached decks, raised decks and anything over roughly 200 square feet require a permit almost everywhere. Building without one risks an order to remove the structure, complicates insurance after any incident, and surfaces during a sale when the buyer's inspector asks for paperwork that does not exist.
Inspections usually happen at three points: footings before concrete is poured, framing before the decking goes down, and a final. Each of those is a free structural review by someone who looks at decks all week, and the footing and framing inspections in particular catch exactly the errors that matter.
It is worth submitting a plan with the sizes from this tool rather than turning up with nothing. The building department will tell you their local requirements — snow load, frost depth, ledger fastening specifics — and those will override anything a web page tells you, including this one.
What this tool assumes
Every number this tool produces rests on these. Change your inputs and they change with you.
- Design load is 40 psf live plus 10 psf dead, the standard residential deck load. Hot tubs, planters, roof structures and heavy snow exceed it and need a designed solution.
- Span figures are the conservative end of published prescriptive tables for No. 2 grade timber. Higher grades span further; this does not assume them.
- Footing size derives from tributary area times 50 psf against the soil bearing capacity you set. Soil varies enormously and a local test beats any default.
- Footing depth is frost depth plus 6 in, with a 36 in minimum. Your building department sets local frost depth.
- This sizes members prescriptively. It is not a stamped engineering design and does not claim to be one.
Mistakes that cause rework
Each of these costs money or a whole weekend to undo.
Fastening a ledger to sheathing or brick veneer
Neither is structural. The ledger must reach the rim joist or framing behind it with fasteners of the specified type and spacing. This is the connection that fails catastrophically.
Skipping the ledger flashing
Water sits on the ledger and rots the rim joist behind it, invisibly, over years. The deck looks fine right up until it comes off the house.
Setting posts in concrete
Embedded posts rot from the inside where nothing shows. Standoff bases keep the end grain clear of standing water and cost a few dollars each.
Footings that stop above the frost line
Frost heave lifts them every winter. The deck racks, the ledger connection works loose, and the damage compounds each season.
Notching guard posts
It removes most of the post's strength exactly where the bending load peaks. Guards must resist 200 lb applied at the top in any direction, and a notched post frequently cannot.
Mixing standard fasteners into treated lumber
Modern treatment chemistry corrodes electroplated steel quickly. Every hanger, screw and bolt in contact with it needs to be hot-dip galvanised or stainless.
Safety & honest limits
- Ledger failure is the leading cause of catastrophic deck collapse, and it happens suddenly under a full load of people. If you cannot positively identify the framing behind the cladding, have this connection done or inspected professionally.
- Guards are required above roughly 30 inches and must resist a 200 lb concentrated load in any direction at the top rail. Post attachment is where site-built guards usually fail this test.
- Footings must extend below the local frost line. Frost heave destroys deck frames over a few seasons.
- Every fastener and connector in contact with treated timber must be hot-dip galvanised or stainless.
- These are prescriptive sizes, not an engineered design. Snow load, unusual geometry, hot tubs and roof structures all require a professional.
Frequently asked questions
What size joists do I need for a deck?
It depends on the span, the spacing and the species. As a rough guide in southern pine at 16-inch centres, a 2x8 spans about 11 ft 11 in, a 2x10 about 14 ft and a 2x12 about 16 ft 6 in under the standard 40 psf live plus 10 psf dead load. The planner on this page applies the full table to your specific span, spacing and species, and shows the table so you can check it.
How far apart should deck joists be?
Sixteen inches on centre is standard and suits most decking. Twelve inches is required for diagonal decking, because laying boards at 45 degrees increases the effective unsupported span by about 41%, and it also lets you use a smaller joist for the same span. Twenty-four inches is permitted for some materials but produces noticeably more bounce underfoot.
How deep do deck footings need to be?
Below your local frost line, plus a little — typically frost depth plus 6 inches, with a 36-inch minimum in most places. A footing that stops above the frost line gets lifted every winter, which racks the frame and works the ledger connection loose. Your building department publishes the local frost depth, and it varies enormously across the country.
Do I need a permit to build a deck?
Almost certainly, if it is attached to the house, raised more than about 30 inches, or larger than roughly 200 square feet. Inspections usually happen at footings, framing and final — each of which is a free structural review by someone who looks at decks every week. Building without a permit risks removal orders and complicates any future sale.
How big should deck footings be?
It comes from the load on each post divided by the soil's bearing capacity. A post carrying 3,000 lb on soil rated 1,500 psf needs 2 square feet of bearing, which is about a 20-inch diameter footing. This tool computes it from your deck geometry and the soil figure you enter; 1,500 psf is the conservative default when the soil is unknown.
Can I attach a deck to my house?
Yes, and most decks are, but the ledger connection is the single most consequential detail in the project. It must fasten into structural framing with specified fasteners and be flashed so water cannot get behind it. A freestanding deck avoids the risk entirely at the cost of two more posts and footings, which is often the better trade for a self-build.
Last reviewed July 25, 2026 · Home & Garden Living
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