板重ねフェンス計算ツール

Board-on-board overlaps each picket over part of its neighbor on the opposite face of the rail, so there is no sightline through the fence from any angle on either side. That overlap, commonly around an inch on a standard 5.5 inch board, tightens the effective picket pitch below the board's own width, which is why this calculator uses width minus overlap rather than the plain width-plus-gap formula a picket count normally runs on. The result is a meaningfully higher board count than a butted privacy layout over the same run, often 20 to 30 percent more, which is the single biggest thing to account for when comparing a board-on-board quote to any other style.

The closest comparison is shadowbox, which also covers both faces of the rail but spaces boards apart with a small gap instead of overlapping them. Board-on-board is fully closed from every angle; shadowbox trades some of that closure for airflow and a somewhat lower board count. Neither changes the post or rail formulas versus the general wood fence calculator, since the overlap or gap only affects the infill boards, not the structure holding them.

Because the extra board count is the real cost driver here, the fence cost calculator is worth running right after this page to see what the overlap actually adds in dollars using your own local lumber prices, rather than guessing at the premium. Rails themselves do not change: the fence rail calculator handles rail count by height and section the same way for board-on-board as for any butted style, since boards on both faces attach to the same rail run.

For a worked picket-pitch example to sanity check the overlap math, how many pickets for 100 feet of fence covers the base formula this calculator adjusts for overlap. The board-on-board vs shadowbox vs solid privacy fence post lays out when the extra board cost of this style is worth it over a plain privacy build, and the wood fence installation guide covers attaching overlapping boards to alternating faces once the count is set. The broader wood fence calculators hub links every other style covered on this site.

The overlap amount is a design choice rather than a fixed number: a wider board can usually carry a larger overlap while staying structurally sound, while a narrower board loses fixing room if the overlap grows too large relative to its width. A proportional overlap, roughly 15 to 20 percent of the board's width, is a reasonable guide for boards wider than the common 5.5 inch picket, with the 1 inch default here best treated as a floor rather than a ceiling.

The labor side of a board-on-board job also runs a bit higher than a butted privacy fence, since attaching alternating boards to both faces of each rail takes more handling per linear foot than nailing a single row flat. That extra labor, on top of the higher board count this calculator already accounts for, is part of why a board-on-board quote commonly comes in above a privacy quote for the same run, and it is worth confirming a quote reflects both factors rather than just the material difference.

Fastening an overlapping board calls for slightly longer nails or screws than a butted board of the same thickness in some cases, since the overlapping board sits proud of the rail by roughly the thickness of the board behind it, and getting fastener length right avoids either a loose board or a fastener that punches through the face. This is a detail worth checking against the specific board thickness being used rather than assuming the same fastener spec as a flat butted fence.

Board-on-board is also one of the styles where buying from a single lumber run matters more than usual, since the overlap narrows the margin for width variation between boards: a batch with noticeably inconsistent actual widths can throw off the even alternating pattern across a long run in a way that is more visible than on a butted fence, where small width differences are less obvious side by side.

Board-on-board is also a common choice where local rules require a finished face toward a neighboring property, since some municipal or HOA fence codes specify that the better-looking side of a fence must face outward or toward the neighbor rather than showing the rail structure. A two-sided style sidesteps that requirement entirely because there is no structural side to hide, which is worth factoring in before defaulting to a one-sided privacy fence in a jurisdiction with that kind of rule.

Spacing the overlap evenly becomes more important than on a one-sided fence as the run gets longer, since any drift in the pitch compounds visibly on both faces rather than just one, making a story pole or a pre-marked layout board worth using on any run longer than a single section.