Published August 18, 2026 · Updated August 23, 2026 · By Tupep
The border is the easy part
A picture frame border looks like four extra boards around the outside of the deck, and four boards is close to the truth for the border itself. What it actually costs you is blocking. A border board runs perpendicular to the field, so on two sides of the deck it runs parallel to the joists with nothing underneath it, and on the other two sides it creates a joint line where every field board ends in mid-air. Neither is fixable after the decking is down.
The width formula
The border and the field have to add up to the deck’s exact width. That gives one equation and one very useful free variable: the border can be ripped to any width you like.
- Field width = rows x face width + (rows minus 1) x gap
- Border rip width = (deck width minus field width minus 2 gaps) / 2
So instead of forcing a strange gap in the field, pick the row count that gives a clean 1/4 in gap and rip the two border boards to whatever closes the difference. That is the whole trick, and it is why a picture frame deck comes out exact when a plain deck cannot.
Worked example: 16 ft x 20 ft deck, 5/4×6
Joists run the 16 ft direction, field boards run the 20 ft direction. The field has to cover the 16 ft width, which is 192 in, minus the two borders and the two gaps beside them.
Try 32 field rows at a 1/4 in gap. Field width = 176 + 7.75 = 183.75 in. Remaining = 192 minus 183.75 minus two 1/4 in gaps = 7.75 in, split between two borders, so each rips to 3-7/8 in. Check: 3.875 + 0.25 + 183.75 + 0.25 + 3.875 = 192.0 exactly.
| Field rows | Field width at 1/4 in gap | Left for both borders | Border width each | Verdict |
|---|---|---|---|---|
| 30 | 172.25 in | 19.25 in | 9-5/8 in | Needs a double-wide border |
| 31 | 178.00 in | 13.50 in | 6-3/4 in | Wider than one board, awkward |
| 32 | 183.75 in | 7.75 in | 3-7/8 in | Clean single rip, use this |
| 33 | 189.50 in | 2.00 in | 1 in | Too skinny to look like a border |
Row 30 is not a failure, it is the option that gives you a double picture frame: one full 5.5 in board plus a 3-5/8 in ripped board with a gap between them. That is a common and good-looking choice on larger decks, and it doubles the border board count.
Border board takeoff
Perimeter is 16 + 20 + 16 + 20 = 72 lineal feet, though the house side usually gets no border because a threshold or skirt covers it, dropping it to 56 ft. Two 20 ft boards and two 16 ft boards cover a full four-sided frame with no joints. We plan 10 to 15 percent extra on border stock because a chipped miter is unusable and you will chip one.
Blocking, the real cost
Two different blocking problems show up, and they need different solutions.
1. Under the border boards that run parallel to the joists
On the two 16 ft ends of this deck, the border runs the same direction as the joists. There is nothing under it except the end joist, and the border is inboard of that. You need a continuous nailer, usually a doubled end joist or a ladder of blocking. That is roughly 32 lineal feet of extra framing lumber, plus the short blocks that tie the ladder back to the first interior joist.
2. Under the seam where field boards meet the border
On the two 20 ft sides, every field board ends at the border line, and that line sits inboard of the rim joist by the border width plus a gap. Nothing is under it. You need a continuous row of blocking between the joists on that line, so each field board end and each border edge lands on solid wood.
Count it: 240 / 16 = 15 bays, so 15 blocks per side and 30 total, each cut to 14.5 in. 30 x 14.5 = 435 in, or 36.25 lineal feet. A 12 ft board yields nine blocks, so four 12 ft boards covers it.
| Added item | Quantity | Reason |
|---|---|---|
| Border boards, 20 ft | 2 plus 1 spare | Long sides, ripped to 3-7/8 in |
| Border boards, 16 ft | 2 plus 1 spare | Short sides, ripped to 3-7/8 in |
| Seam blocking, 12 ft stock | 4 boards, 30 blocks | Under the field-to-border joint, both long sides |
| Ladder nailer, 16 ft stock | 2 boards plus tie blocks | Under borders running parallel to joists |
| Face screws or plugs | about 250 extra | Hidden clips do not work at the perimeter |
Field boards get shorter, and that is waste
Each field board now runs 240 minus 11.5 = 228.5 in, or 19 ft 1/2 in. You still buy a 20 ft board for every row and throw away 11.5 in. Across 32 rows that is 368 in, or 30.7 lineal feet of decking in the offcut pile. On a plain deck those same 32 boards would have zero waste. That is the number people miss when they price a picture frame as “four extra boards.”
Two things that make it look right
Hidden fasteners stop at the border. Clip systems need a grooved edge on both sides, and the border’s outer edge and the miter joints have neither. Plan on color-matched face screws or a plug system around the whole perimeter and count them separately. Mixing a clipped field with a face-screwed border is normal and expected.
Pre-drill at the miter tips. The last two inches of a 45 degree miter is a thin wedge, and driving a screw into it without a pilot hole splits it every time. We drill the tip, set the fastener, then set a second one 4 to 6 in back so the point cannot lift.
Related guides
- Composite vs Wood: Board Length and Waste
- How Many Deck Boards for a 12×16 Deck
- Deck Framing Lumber List for a 10×12 Deck
- Post Spacing: 6 ft vs 8 ft
Sources and Further Reading
Run your own numbers with the Deck Board Calculator, or browse every tool on the calculators index. Coverage figures and material constants are cross-checked against manufacturer technical data sheets before publication. See our Methodology page for how figures are selected and verified.
Planning estimate only. Results assume standard conditions and are intended for material planning. Verify against your product’s technical data sheet and your local building code before purchasing. Structural, electrical, and gas work should be specified by a licensed professional.
Last updated: August 23, 2026
Leave a Reply