Summary

Feather-edge board installation is the core skill in close board and traditional timber fencing. The boards themselves are straightforward — tapered softwood planks that any joiner would recognise — but the installation has a sequence logic that, done wrong, either splits boards or creates a fence that opens up as the timber dries and moves.

The overlap method is not just about coverage; it creates a weatherproof assembly by ensuring rain driven against the fence face always hits a lapped joint rather than a through-gap. The direction of lay (thick edge to prevailing weather or thick edge to non-prevailing, depending on construction convention) affects which face sees the most wear. The nailing pattern matters because feather-edge boards move significantly with moisture: a board fixed through both the overlap and its own body is restrained and will split when it swells.

This article walks through board selection, arris rail layout, installation sequence, and the finishing details that separate a fence that looks good after five years from one that looks tired after two.

Key Facts

  • Board dimensions — standard widths: 100 mm, 125 mm, 150 mm; length 1.8 m standard; 900 mm, 1.2 m also available
  • Taper — thick edge approximately 16 mm; thin edge approximately 5–6 mm (some premium boards specify 19 mm thick edge)
  • Overlap — minimum 25 mm per BS 1722-5; in practice 25–38 mm is common; greater overlap uses more boards but gives better coverage at the joints over time
  • Coverage calculation — for 100 mm boards with 25 mm overlap, effective coverage per board = 75 mm; for 1 m of fence face width, 14 boards needed (1000/75 = 13.3, round up)
  • Material quantity — for a 10 m fence at 1.8 m height: approximately 135 × 100 mm boards, or 110 × 125 mm boards
  • Arris rail heights — bottom rail: 150–200 mm above gravel board level; top rail: 150 mm below board tops; middle rail: equidistant for 3-rail setup; four rails for fences over 1.8 m
  • Nailing — two galvanised 65–75 mm ring-shank or spiral nails per rail crossing; one nail only per board per rail (not pinning to adjacent board)
  • Nail corrosion — use hot-dip galvanised ring-shank nails; standard bright steel nails stain boards with rust streaks within 12–18 months on UC3-treated softwood
  • UC3 treatment — feather-edge boards for external use must be pressure treated (tanalised) to UC3 minimum; not UC2 indoor grade
  • Spacing from ground — boards should clear soil by minimum 50 mm via a gravel board; boards in contact with soil rot at the base within 3–5 years
  • Capping rail — 75 × 38 mm planed capping rail nailed over board tops, protecting exposed end grain from water ingress
  • Board faces — sawn face (rougher) is traditionally placed on the inside; planed or smooth face to the outside; though convention varies by region

Quick Reference Table

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Board Width Min Overlap Coverage per Board Boards per Metre Run Boards per 10m × 1.8m Fence
100 mm 25 mm 75 mm 13.4 ~135
125 mm 25 mm 100 mm 10 ~100
150 mm 25 mm 125 mm 8 ~80
100 mm 38 mm 62 mm 16.1 ~162
125 mm 38 mm 87 mm 11.5 ~115

Detailed Guidance

Arris Rail Layout and Board Start Point

Before fitting a single feather-edge board, fix all the arris rails and check that they form a flat plane. Rails that bow or twist will cause boards to follow the bow, creating a rippled fence face.

Setting out the arris rails:

Set out the three-rail positions for a 1.8 m fence: top at 1.650 m above the gravel board (150 mm below fence top), bottom at 150–200 mm above the gravel board, middle equidistant (approximately 700–725 mm). Use a chalk line or laser level along the fence run to mark the rail height on each post before fitting. This check takes 10 minutes and prevents building a complete bay only to find the boards won't run true because one rail sags.

Starting the first board:

Decide whether to start from the structure end or the open end of the fence run. For a fence that terminates at a building wall, start at the wall end — the last board in the run can be trimmed to fit, and the cut end is less visible. For a free-standing fence, start from the most visually prominent end (usually the end seen from the gate).

Set the first board vertical using a spirit level. The thick edge should face the direction you intend the fence to present — the overlapping pattern means the thick edge of each subsequent board covers the thin edge of the previous one.

Nailing Technique: The One-Nail Rule

This is the most important technique point in feather-edge installation. Each board is nailed through its own body into the arris rail; it is NOT pinned to the board behind it.

Why this matters: Feather-edge boards are green (wet) softwood when bought. They dry down in service, shrinking across the grain. If you nail board B through both its own body and through board A behind it (pinning the overlap), you constrain both boards. When they dry, the board splits at the nail point, opens up the overlap, or pulls the nail out. A fence built this way shows splits and gaps within 12 months.

Correct method: Hold board B against board A with the correct overlap. Drive one nail through the thick edge of board B, through the overlap zone, into the arris rail. The nail passes through board B only — it does not pin board A. Repeat at each arris rail crossing. Board A is free to move independently; board B is free to move independently. Overlaps remain intact as both boards shrink.

Nail selection: 65 mm × 3.1 mm ring-shank or spiral galvanised nail, hand-driven or air gun. Ring-shank nails provide far better pull-out resistance than smooth shank — important on feather-edge boards where the nail is driven into the relatively thin section of the arris rail triangular profile.

Maintaining Vertical Alignment

Feather-edge boards are nominally identical but in practice vary slightly in width due to sawing tolerances. A cumulative drift of 2 mm per board adds up to 20 mm error over 10 boards — enough to put the fence visibly out of square.

Checking alignment: Every 5–6 boards, step back and sight along the fence face to check boards are still running true vertical. Alternatively, use a plumb bob or digital level on each board. If drift is occurring, adjust slightly by varying the overlap — increase or decrease by 2–3 mm per board to correct back to true vertical over the next 5–6 boards. Abrupt corrections look worse than gradual ones.

Uneven board widths: Sort boards before installation and discard any that are badly bowed or significantly underwidth. On a 100 mm board, more than 3 mm under nominal width causes visible variation in the overlap pattern.

Top Edge and Capping

The tops of feather-edge boards are the most vulnerable point to moisture ingress. End grain absorbs moisture rapidly, swells unevenly, and is the point where splits typically initiate. Two details address this:

Board tops at consistent height: Set boards so tops are at the same height within each bay. Drive a temporary nail in the post at the target height and rest each board on it while nailing. A fence where boards vary in height by 20–30 mm across a run looks amateurish.

Capping rail: A 75 × 38 mm planed timber capping rail nailed over the tops of all boards is standard specification per BS 1722-5. Nail it down onto the board tops at 300 mm intervals using 75 mm galvanised nails. The cap protects end grain, unifies the top edge visually, and is far easier to renew than full boards. Cut the capping at a 45-degree angle at each post face to shed water and for appearance.

Some installations omit capping and use a pointed top (arrowhead) profile on the feather-edge boards instead — boards cut to a point. Pointed tops shed water from the end grain slightly better than square-cut tops but are more expensive and still benefit from capping for maximum longevity.

Finishing

After all boards and capping are fixed, apply a timber preservative and finish coat if the boards are not pre-coated. Fence treatment (Sadolin, Ronseal, Cuprinol or equivalent fence treatment) should be applied to the full fence face while the timber is dry, typically in spring or late summer — not in rain or when the timber surface is damp.

For the client, note that most manufacturers of pressure-treated timber recommend applying an additional coat of fence treatment within 12 months of installation, once the timber has dried out from the factory treatment process.

Frequently Asked Questions

How many feather-edge boards do I need per metre of fence?

For 100 mm boards with standard 25 mm overlap: 14 boards per metre of fence face (1000 ÷ 75 mm coverage = 13.3; round up). For 1.8 m fence height, one board per row at 1.8 m long covers the full height. So for 10 m of fence at 1.8 m height: 10 × 14 = 140 boards (plus 10% waste allowance = 155 boards). See the coverage table above for other sizes.

Should the smooth face or rough face of feather-edge boards go outward?

Convention varies regionally and by client preference. The rough-sawn face is more open-grained and absorbs treatment better; some fencers put it outward to improve treatment penetration on the weather-exposed face. Others put the planed/smooth face outward for appearance. Structurally there is no difference. Be consistent within a run.

The boards are moving in the wind — is that normal?

Some movement in high winds is expected on a tall fence. If individual boards rattle or flex significantly, check: (1) the nails have not pulled through (boards are only fixed at one rail); (2) the arris rails are sound and fixed properly to posts; (3) the posts themselves are not rocking. The close board assembly gets more rigid as the boards dry and pack together, but if posts are loose, no amount of board fixing will resolve the issue.

Regulations & Standards

  • BS 1722-5 — Specification for close-boarded fences; board dimensions, overlap, treatment, and construction requirements

  • BS 8417 — Preservation of wood: code of practice; Use Class specification for feather-edge boards (UC3 for above-ground exterior)

  • BS EN 335 — Durability of wood and wood-based products: use classes and definitions

  • BS 1722-5 Specification — BSI — British Standard for close-boarded fences

  • Forest Research — Wood Properties and Timber Treatment — timber moisture content, treatment penetration and preservative specification

  • Tanalith E Technical Guide — Lonza Wood Protection — UC3 treatment specification for feather-edge boards

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