Decks and porches
Updated 5 min readWorks without an account
A deck is a raised wood platform with its own framing: joists, a beam, posts and footings, worked out for you from the IRC 2021 span tables. Add one from the library, set its height, and FloorGen draws the framing, the guard and the stairs, checks them, and lists the lumber to buy.
Add a deck
- Step 1: Pick the library entry
In the library, open Structure › Railings, balconies & ramps and click Deck (fits to wall), or drag it onto the plan. Next to an outside wall it is built against that wall with a ledger; anywhere else it is freestanding.
- Step 2: Set the height
In the panel, type Top above ground. Over 30 in (76 cm) the open edges need a guard and the deck needs stairs to the ground.
- Step 3: Add stairs
Click Stairs, far side, Stairs, left or Stairs, right. The number of risers follows the height, at 7 3/4 in or less each.
- Step 4: Size the framing
Click Size from IRC tables to pick the smallest joists and beam that span the deck. Show framing on the plan swaps the boards for the joists, beam, posts and footings.
What the checks look at
| Check | Rule |
|---|---|
| Guard | Open edges more than 30 in above the ground need a guard at least 36 in high (IRC R312.1). Opening gaps stop a 4 in sphere. |
| Joist span | Table R507.6, southern pine No. 2, 40 psf live load, 10 psf dead. 2x8 at 16 in spans 11 ft 10 in. |
| Cantilever | Joists may reach past the beam by a quarter of their span at most (R507.6). The table’s own cantilever columns depend on the back span: check them. |
| Beam and posts | Table R507.5 sets how far a beam spans between posts; posts are spaced to fit, sized by Table R507.4 and footed by Table R507.3.1 (60 psf row, 1500 psf soil). |
| Ledger | Against its house wall, not on a glazed or curved wall, and under the IRC not on stone or masonry veneer (R507.9.1.1). Lag screws into the band joist are spaced by Table R507.9.1.3(1), 1/2 in lag with 1/2 in sheathing: 30 in apart for joists up to 6 ft down to 10 in at 16 to 18 ft. Past 18 ft the table stops: ask an engineer. |
| Stairs | Riser 7 3/4 in at most, tread 10 in at least, 36 in wide, a handrail from four risers (R311.7), a landing above 151 in of rise (R311.7.3). |
Guard and stair findings cite the rule of the project’s code profile; the R507 span checks are the IRC’s and run only under the IRC profile. With a lot grade set (site settings), posts, stairs and the guard rule follow the ground under the deck; the deck’s height is measured from the datum, the grade at the house.
The span tables assume southern pine and a 40 psf live load. Check your species, ground snow load, soil, frost depth and local amendments before you file a permit set: these checks guide the design and are not an engineer’s sign-off.
A covered porch
Switch on Roof over the deck for a shed roof over the whole deck, high at the house, on posts at the outer corners. For a roof hung on the house wall itself, use a pent roof in the roof settings (see Roofs).
Materials list
The schedules and the takeoff list decking boards, joists, beam plies, posts and ledger by size and length, footings and concrete, and an approximate count of hardware. Lumber lengths round up to the next even foot; counts are for buying, not a cut list.
Questions
Can an AI assistant build one?
Yes: add_deck and update_deck take a wall, size, height, stairs and porch, e.g. a 12 by 16 ft deck off the kitchen, 4 ft up, with stairs to the yard.
Why does the deck say my joists are too long?
The span from the ledger or first beam to the outer beam is more than the table allows for that size and spacing. Pick bigger joists, closer spacing or Size from IRC tables.