Article — Board-on-Board Fence Calculator
Board-on-Board Fence Calculator: Privacy Done Right
A board-on-board fence uses two layers of vertical pickets with 1-inch overlap to eliminate sight gaps. A 100-foot, 6-foot tall fence with 1×6 boards needs about 267 boards per side — 534 total — plus 14 posts and 22 cubic feet of concrete.
Board-on-board (also called shadowbox) is the most-installed privacy fence style in suburban North America. It hides views from both sides, looks finished from inside or out, and uses standard 1×6 lumber. The math gets you to the material list; the article below explains the trade-offs that make this style worth its 2× cost premium over standard plank fencing.
What is a board-on-board fence?
A board-on-board fence is built in two layers. The back layer has vertical pickets nailed to the inside face of the rails, spaced with small gaps between adjacent boards. The front layer is offset so each board centers over a gap in the back layer. Front boards overlap the back boards by an inch on each side, completely blocking any line of sight through the fence.
The result is 100% privacy with no see-through gaps even when wood shrinks in dry seasons. From a perpendicular angle the fence looks like a flat plank wall; from an oblique angle the depth becomes visible as alternating shadow lines — hence the alternative name "shadowbox fence."
Standard board fences shrink and reveal sight gaps within their first dry season. Western red cedar shrinks roughly 4-5% across the grain as it dries from 25% moisture (fresh) to 8% moisture (seasoned). A 5.5-inch board becomes 5.2 inches — enough to create 0.3-inch gaps in a tight fence. The 1-inch overlap on board-on-board absorbs all of that and more.
Board-on-board fence math
The effective spacing per pair of boards equals board width minus overlap. With 1×6 boards (5.5 inch actual) and 1-inch overlap: effective period = 4.5 inches. For a 100-foot run that's 100 · 12 / 4.5 = 267 boards per side, or 534 total.
effective = w_board − w_overlap front-to-front spacingboards/side = ceil(L / effective) per layertotal = 2 × boards/side both layersposts = ceil(L / spacing) + 1 structureEach board runs the full fence height. A 6-foot fence with 534 boards uses 3,204 linear feet of picket lumber. At 1×6 nominal stock, that's about 1,600 board feet plus 100 board feet of rail stock, totaling around 1,700 BF for a moderate-sized residential fence.
Board-on-board vs. other privacy fences
Four privacy fence styles dominate residential construction. They differ in cost and effectiveness.
- Standard plank: Single layer, boards edge-to-edge. Cheapest but gaps appear after first dry season.
- Tongue-and-groove: Boards lock together via milled edges. Permanent privacy but boards cost 50% more.
- Board-on-board: Two layers with overlap. 2× boards but no gap risk, attractive from both sides.
- Stockade: Single layer with narrow pointed pickets. Decorative, partial privacy.
- Vinyl panel: Pre-fabricated 6 or 8 ft panels. Quick install, $25-40 per linear foot.
- Composite: Engineered wood-plastic boards in any pattern. 2-3× material cost but zero maintenance.
Board-on-board fence materials
Wood choice drives lifespan and aesthetics.
Cedar is the premium choice — naturally rot-resistant heartwood lasts 25-30 years even in damp climates. Pressure-treated pine costs a third as much but only lasts 15-20 years and requires annual staining to keep looking presentable. Composite (Trex Fence, TimberTech) doubles material cost but never needs paint, stain, or replacement and lasts 25+ years with no maintenance.
Board-on-board fence installation
Seven steps to install a board-on-board fence correctly:
- Mark the fence line with stakes and string. Check for property lines, easements, and underground utilities (call 811).
- Dig post holes 8 feet on center, 24-36 inches deep depending on frost depth.
- Set 4×4 (or 6×6 for tall fences) posts in concrete. Plumb each with a level. Cure 48 hours.
- Attach top and bottom rails (2×4) horizontally between posts.
- Nail back-layer pickets to the inside face of rails, spaced 3-4 inches apart.
- Nail front-layer pickets to the outside face, centered over gaps in the back layer.
- Cap the top of each post with a decorative cap and apply stain or sealer within 30 days.
Set posts 24 hours before attaching rails or boards. Concrete needs to cure or the post can drift out of plumb when you start hanging weight on it. A stiff breeze during the first 8 hours is enough to push an uncured post out of alignment.
Board-on-board fence cost
For 2026 in the central US: $25-40 per linear foot installed for pressure-treated; $50-75 per linear foot for cedar; $90-120 per linear foot for composite. A 100-foot board-on-board fence in cedar runs roughly $5,000-7,500 installed.
DIY saves 40-50% on labor but takes 2-3 weekends for a moderate run. Material cost only (no labor): roughly $15-20 per linear foot for pressure-treated, $30-40 for cedar. Don't forget concrete ($25-30 per post) and post caps ($3-8 each) — small line items that add 10% to the total.
Common board-on-board fence mistakes
Six errors show up on inspection reports and call-back lists:
Setting posts and hanging boards the same day saves a day but ruins the fence. Wet concrete shifts under weight; posts drift out of plumb; gaps open at the top of the fence. Pour concrete one weekend, hang boards the next.
- Hanging boards before concrete cures: Posts drift out of plumb; fence develops gaps at the top.
- Wrong post depth: Below the frost line is non-negotiable in cold climates.
- Underspecified board overlap: Less than 1 inch may reveal gaps after seasonal shrinkage.
- Wrong fastener: Galvanized nails stain cedar; stainless or hot-dipped galvanized only.
- No top cap: End grain absorbs water and rots posts from above. Always cap.
- Boards touching ground: Leave 1-2 inches of clearance. Wood touching soil rots fast.
- Skipping the gravel base in post holes: Without drainage, water pools at the post bottom and accelerates rot.
Board-on-board fence maintenance
Five tasks keep a board-on-board fence looking new for decades:
- Stain or seal every 2-3 years: Cedar and pressure-treated both benefit. UV destroys the surface lignin and turns wood gray without protection.
- Inspect post bases annually: Look for cracks, settling, or rot at grade level. Catch problems before they spread.
- Clear vegetation away from the fence: Vines and shrubs trap moisture against the wood and accelerate rot.
- Replace damaged boards individually: Pulling one rotten board is cheap; replacing 20 at once is a project.
- Tighten loose fasteners: Wood movement loosens nails over years. Driving them back in every few years prevents board sag.
- Power-wash before staining: Surface dirt and oxidation block stain absorption. A 1500-PSI wash with mild detergent restores the surface.