Summary

Close board fencing is the UK's most widely installed domestic fencing system. Drive down any residential street built in the last 40 years and the chances are that the rear garden boundaries are close board — overlapping vertical softwood boards creating a robust, private, and aesthetically acceptable barrier at a price point accessible to most homeowners.

Despite its ubiquity, close board is routinely installed badly. The most common failure modes are posts set too shallow, arris rail joints sited at the same height on adjacent panels (creating a line of weakness), no gravel boards leaving boards in contact with soil, and the use of untreated or inadequately treated timber that begins to rot within five years. Doing the job properly costs marginally more in materials and slightly more in time, but produces a fence that lasts two decades rather than one.

This article covers specification to BS 1722-5, post setting methods, construction sequence, and common failure modes to avoid. It also addresses the homeowner questions about planning permission and neighbour rights that fencing installers deal with on virtually every job.

Key Facts

  • Governing standard — BS 1722-5: Specification for close-boarded fences
  • Post spacing — maximum 3 m centres; 2.4 m to 2.7 m is more typical for standard board lengths
  • Post size (timber) — minimum 100 × 100 mm section for 1.8 m fence height; 125 × 125 mm for exposed sites or heights over 1.8 m
  • Post size (concrete) — minimum 100 × 100 mm slotted or morticed concrete posts; standard lengths 2.4 m (for 1.8 m fence) and 3.0 m (for 2.4 m fence)
  • Post ground depth — minimum one-third of total post length; 600 mm for a 1.8 m fence (total post length 2.4 m); 750 mm for windier sites
  • Arris rail size — 100 × 75 mm (nominal) triangular profile; two rails for up to 1.5 m height, three rails for 1.5–1.8 m, four for over 1.8 m
  • Feather-edge board width — 100 mm, 125 mm, and 150 mm are standard; 100 mm most common for domestic close board
  • Feather-edge board thickness — tapered: thick edge 16 mm minimum, thin edge approximately 5–6 mm
  • Overlap — minimum 25 mm overlap between adjacent boards; 25% of board width is a practical guide
  • Gravel board — 150 × 38 mm or 200 × 38 mm timber or concrete gravel board fixed at the base, keeping feather-edge boards off the ground
  • Capping rail — 75 × 38 mm timber capping rail nailed over board tops protects end grain and extends fence life
  • Treatment standard — UC4 (Use Class 4) for ground contact elements (posts, arris rails if close to ground); UC3 for above-ground elements (feather-edge boards, capping)
  • Green oak — acceptable alternative for posts; naturally durable; does not require treatment
  • Post concrete — C20 or ST2 mix; minimum 150 mm aggregate around post base or concrete haunching; concrete should be crowned above ground to shed water away from post
  • Maximum fence height without planning — 1 m adjacent to a highway (road, pavement), 2 m elsewhere; see planning-permission article for full details

Quick Reference Table

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Fence Height Post Size Post Depth Rails Required Typical Post Length
Up to 1.2 m 75×75 mm min 450 mm 2 arris rails 1.8 m
1.5 m 100×100 mm 525 mm 2 arris rails 2.1 m
1.8 m 100×100 mm 600 mm 3 arris rails 2.4 m
2.0 m 125×125 mm 650 mm 3 arris rails 2.7 m
2.4 m 125×125 mm 750 mm 4 arris rails 3.2 m

Detailed Guidance

Post Setting

Posts are the most critical element — a close board fence falls apart at its weakest post, and weak posts are almost always the result of incorrect setting depth or poor concrete specification.

Dig depth: Use the one-third rule as a minimum. For a 2.4 m post, dig to 600 mm. On sites with loose or sandy soil, chalk, or where wind exposure is significant, increase to 750 mm. A fence in an open garden on a hill catches substantially more wind load than one sheltered by adjacent buildings.

Concrete vs postcrete vs dry-pack: All three methods work if done correctly.

  • Wet concrete (C20 mix): most durable for timber posts; fill hole to within 75 mm of surface, then crown with additional concrete sloping away from the post to shed water
  • Postcrete (fast-setting bag mix): convenient and strong if used correctly; pour dry granules in hole, add water, allow to set before loading; do not disturb for 30 minutes minimum
  • Dry-pack (gravel + lean mix): acceptable in well-drained soil; not recommended on clay or in areas with high water table

Concrete posts in slots: Slotted concrete posts accept arris rails and boards directly into the slot. Timber posts require arris rail brackets or mortice joints. Concrete posts are more durable at the base (no timber rot at ground level) but are heavier to handle and less forgiving if set slightly out of alignment.

Level and line: Set the corner and end posts first, string a line, and set intermediate posts to the line. Check plumb in two directions — a post that looks plumb one way can be out 5 mm the other way. For long fence runs, allow for gradient: posts should step down to follow the ground contour rather than having the fence fly out at the top at a low point.

Arris Rail and Board Installation

Arris rails run horizontally between posts, carrying the vertical boards. On a 1.8 m close board fence, three rails are standard: top rail 150 mm from the fence top, bottom rail 150–200 mm above the gravel board, middle rail equidistant between them.

Rail positioning on timber posts: Fix rails using pressed steel arris rail brackets (galvanised or stainless) rather than through-nailed mortice joints, unless the client specifically requests morticed joints (more traditional but susceptible to water ingress at the joint if poorly made).

Rail staggering: Never site arris rail joints (butt joints between rail lengths) directly above one another. Offset the joint heights between adjacent bays — top rail joint in bay 1 at post A, bottom rail joint in bay 1 at post B. This prevents a line of structural weakness along the fence run.

Gravel board: Fix the gravel board first, level across the base of each bay. Use a 150 × 38 mm timber gravel board or a precast concrete gravel board. The gravel board lifts feather-edge boards clear of soil contact — without it, the board bases rot within 3–5 years regardless of treatment. Fix timber gravel boards to the posts with two screws each end; concrete gravel boards slot into slotted concrete posts.

Feather-edge boards: Start at one end, fix the first board with the thick edge to the prevailing weather side (the side the rain hits), thin edge inboard. Nail through the thick portion of each overlapping board into the arris rail using two galvanised ring-shank or spiral nails per rail crossing. Do not nail through both boards at an overlap — this causes boards to split as they expand and contract. Check vertical with a level every 5–6 boards.

Capping rail: Nail a 75 × 38 mm planed capping rail over the tops of the boards, centred, with the flat face up and slightly chamfered at each end for drainage. This protects the exposed end grain of the feather-edge boards, which is where moisture ingress and rot begin.

Timber Treatment

Treatment specification is critical for longevity. The Use Class system (based on BS 8417 and BS EN 335) defines the risk environment:

  • UC3 — above ground, exposed to weather (feather-edge boards, capping, gravel boards above soil): vacuum/pressure treated CCA or Tanalith equivalent; preservative retention for softwood minimum 9 kg/m³ permethrin equivalent
  • UC4 — in ground contact (posts, bottom of arris rails near soil level): UC4 treatment; retention 9 kg/m³ boron equivalent or Tanalith E equivalent

Most commercially supplied close board fencing components are sold as "pressure treated" or "tanalised" — confirm the Use Class and treatment chemical from the supplier rather than relying on the description. Budget timber often receives UC2 (indoor use) or minimal UC3 treatment that is inadequate for UK outdoor conditions.

Factory treatment vs field application: Factory pressure-treated (vacuum impregnated) timber is far superior to brushed or dipped treatment applied on site. Any cuts made on site expose untreated heartwood at the cut face — treat all cut ends immediately with an end-grain preservative before installation.

Frequently Asked Questions

How long should a well-built close board fence last?

With UC4 posts (or concrete posts), UC3 boards, concrete gravel boards, and galvanised fixings, a close board fence should last 20–25 years before requiring significant intervention. The first component to fail is usually a post or two — replaceable without removing the whole fence. A fence built with inadequately treated timber or posts set too shallow may need replacing in 8–10 years.

Who is responsible for a boundary fence?

Boundary ownership is determined by the title deeds. The "T" mark on a title plan indicates ownership of the boundary, with the foot of the T on the owning side. However, many UK properties have no clear T marks. Without deeds evidence, there is no automatic rule that the "good side" (boards facing outward) indicates ownership. Advise clients to check their deeds before starting work on a shared or ambiguous boundary.

Can I use metal posts instead of timber or concrete?

Yes — galvanised steel drive sockets (Metpost or similar) set into the ground are an alternative to concrete-in posts for lighter fence systems. For close board at 1.8 m height, use at minimum a 75 × 75 mm Metpost socket set to the manufacturer's recommended depth, with additional concrete backfill for stability. Metpost drive sockets do not perform as well as concreted posts in clay soils where the socket can work loose with frost heave over time.

Do I need planning permission for a close board fence?

1.8 m close board to the rear or side of a domestic property falls within Permitted Development and does not require planning permission. Fences adjacent to a highway (including a public footpath that abuts the property) are limited to 1 m without permission. For listed buildings or properties in Conservation Areas, all boundary works may require consent — advise the client to check with their local planning authority.

Regulations & Standards

  • BS 1722-5 — Fences: specification for close-boarded fences; governs dimensions, material specification, and construction

  • BS 8417 — Preservation of wood: code of practice; Use Class framework for timber treatment specification

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

  • Town and Country Planning Act 1990 / GPDO 2015 Schedule 2 Part 2 — Permitted Development rights for gates, fences, walls and means of enclosure

  • BS EN 12372 / BS EN 1317 — reference standards for concrete fence posts (strength and durability)

  • BS 1722-5 Specification for Close-Boarded Fences — BSI — British Standard governing close board fence specification

  • Timber Research and Development Association (TRADA) — timber treatment guidance and Use Class reference tables

  • Planning Portal — Fences, Gates and Garden Walls — Permitted Development guidance for boundary structures

  • Tanalith E and Lonza Wood Protection — Technical Data — preservative treatment specifications for pressure-treated timber

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