Trellis and Panel Fencing: Specification, Installation and Common Problems

Quick Answer: Panel fencing uses prefabricated 1.83 m wide × 0.9–1.8 m high panels of lapped or woven boards between posts at 1.83 m centres; trellis panels use an open diagonal or square lattice framework. Both are governed by BS 1722-11. Standard panel fencing is less durable than close board construction and requires UC4-treated posts and concrete gravel boards — panels standing in soil will rot at the base within 3–5 years.

Summary

Panel fencing is the fastest fence to install and the first to be replaced. The construction — prefabricated panels of lapped softwood boards screwed or nailed into a softwood frame — allows a garden fence to be erected in an afternoon, but it is structurally weaker than close board. The lapped boards are thin (usually 7–9 mm), the frame is light, and the panels flex in high winds. On exposed sites or in gardens with large dogs or persistent climbing plants, panel fencing typically lasts 10–15 years at most before the frames begin to fail.

Trellis has a different primary function: providing a surface for climbing plants rather than privacy or security. Trellis panels are inherently non-structural and should not be used as a boundary fence in isolation (unless specifically specified as a privacy screen at low height). Combined with solid fencing below, trellis is an effective way to increase the effective height of a fence without triggering planning permission issues for solid screens over 2 m.

This article covers installation standards, the post-setting requirements that most panel fence installers get wrong, weathering and replacement considerations, and the planning grey area around trellis topping on existing fence posts.

Key Facts

• BS 1722-11 — Specification for wooden fence panels; governs construction and performance of prefabricated panel fencing
• Standard panel dimensions — 1830 mm wide (6 ft) × 900 mm, 1200 mm, 1500 mm, 1800 mm high; some manufacturers offer metric sizes (1800 mm wide)
• Panel types — lapped (horizontal boards lapped over each other); woven (horizontal boards woven around vertical laths); feather-edge panel (vertical feather-edge boards on a frame); hit-and-miss (alternating vertical boards with gaps)
• Frame timber — typically 47 × 47 mm or 50 × 50 mm frame; check for UC3 treatment; many budget panels use untreated or inadequately treated timber
• Board thickness — lapped panels: 7–9 mm boards; woven panels: 6–8 mm; feather-edge panel boards: 10–12 mm
• Post spacing — exactly 1830 mm from inside face to inside face of posts for standard panels; confirm against actual panel dimensions before setting posts
• Post size — 100 × 100 mm minimum for 1.8 m panel fence; concrete posts or 100 mm timber UC4-treated
• Post depth — minimum 600 mm for 1.8 m fence; 750 mm on exposed sites
• Gravel board — essential; panel base must be off the ground; concrete gravel board minimum 150 mm deep
• Panel fixing — panels slot into slotted concrete posts, or fix to timber posts with panel clips (joist hangers or purpose-made panel brackets), or screw through panel frame into timber post
• Trellis sizes — typically 1830 mm wide × 300 mm, 600 mm, 900 mm, 1200 mm, 1800 mm high; lattice 25×25 mm or 38×38 mm square or diamond pattern
• Trellis construction — 12–16 mm lath nailed or stapled at crossing points; 35–47 mm perimeter frame
• Trellis fixing — fix to fence top by slotting into post if post is taller, or by screwing to post face; do not rely on gravity
• Planning height — solid panels + trellis: planning officers treat the total height as the fence height for PD assessment; a 1.8 m solid fence with 300 mm trellis topper is 2.1 m total and requires planning permission (above 2 m limit for non-highway positions)

Quick Reference Table

Detailed Guidance

Installation Sequence for Panel Fencing

The critical difference from close board installation is that the post spacing must match the panel width precisely before any post is set in concrete. If posts are set 1850 mm apart when panels are 1830 mm wide, the panels will not fit — you cannot adjust post position once concrete is poured.

Pre-setting check: Before digging the first hole, measure 3–4 actual panels from the supplied delivery. Panel widths vary ±15 mm between manufacturers. Set post centres based on measured panel width, not catalogue specification.

Installation sequence:

1. Set the first corner or end post; brace plumb; allow concrete to partially set (2 hours)
2. Measure exactly one panel width (inside face measurement) from the first post; mark the second post position
3. Check that this measurement places the second post on line with the first; set the second post
4. Continue bay by bay — measure from the previously set post for each subsequent post
5. After all posts are set and concrete cured (minimum 48 hours), install gravel boards
6. Drop panels into slotted posts from the top, or fix with panel clips to timber posts

Slotted post system: Concrete slotted posts are the correct specification for panel fencing — the panel frame slides directly into the slot without additional fixing. Confirm the slot width matches the panel frame thickness (typically 47 mm slot for 47 mm frame; some budget panels have 38 mm frames requiring different posts).

Timber post panel clips: Where timber posts are used, stainless or galvanised panel clips (L-shaped brackets screwed to the post face) provide the fixing. Use minimum 4 clips per panel — two on each post. Pre-drill the panel frame to prevent splitting.

Wind Loading and Panel Failure

Prefabricated panels fail because the frame-to-board fixings loosen over time, allowing boards to rattle and eventually detach, and because the frame joints (corners) weaken with moisture cycling. The boards themselves may still be serviceable when the frame has failed.

Reducing wind damage:

• On exposed sites, specify hit-and-miss panels (with gaps between boards) rather than solid lapped panels; the wind passes through rather than loading the panel face
• Ensure post-to-ground depth is 750 mm (not 600 mm) on sites with regular strong winds
• Apply annual fence treatment to maintain timber integrity in the frame joints

Replacing individual panels: One of the advantages of panel fencing over close board is that a failed panel can be replaced without disturbing adjacent bays. With slotted concrete posts, simply lift the failed panel out from the top and slide a replacement in. With panel clips on timber posts, unscrew the clips and remove the panel.

Trellis: Uses and Limitations

Trellis panels are correctly used as:

• Climbing plant support on a wall or fence face (fixed 50–75 mm proud of the surface for plant growth)
• Decorative screen at low height (up to 1.2 m) where full privacy is not the requirement
• Topper on an existing fence (provided total height is within planning permission limits)
• Training frame for espalier fruit trees or wall shrubs

Trellis is not suitable as:

• A boundary fence without a solid base (wind deflects light trellis out of any fixing)
• A security fence (any person or animal walks through it)
• A support for heavy climbers without additional structural support — wisteria, Virginia creeper, and mature climbing roses generate significant weight and wind leverage; fix trellis with robust galvanised screws into treated battens fixed to the wall or fence frame

Fixing trellis proud of walls:

The gap between trellis and the wall or fence it is fixed to is critical for plant health — climbing plants need air circulation behind their stems to resist fungal disease. Fix 50 × 50 mm timber battens to the wall face at 600–900 mm centres, then screw the trellis to the battens. This provides the 50–75 mm air gap and makes trellis removal for wall maintenance straightforward.

Planning and trellis:

The planning height debate around trellis toppers is genuinely ambiguous. Planning Policy Guidance states that the height of a fence includes any trellis or other additions. However, enforcement practice varies between local authorities — some treat open trellis as non-material because it cannot form a solid visual barrier; others apply the rule strictly. Advise clients that adding trellis to bring total height above 2 m adjacent to a highway (1 m limit) or above 2 m elsewhere is technically planning-relevant and they should check with their local planning authority before proceeding.

Maintaining Panel Fencing

Apply timber fence treatment (Cuprinol, Ronseal, Sadolin or equivalent) annually or every other year to maintain the preservative protection in panel frames and boards. Pay particular attention to:

• Panel frame end grain at the top and bottom edges
• Gravel board upper face (faces upward, collects water)
• Capping rail end cuts

Treat in late spring or early autumn when the timber is dry — not immediately after rain and not in frost. Fence treatment soaks into open-grained timber; a second coat applied 2–4 hours after the first significantly improves protection.

Frequently Asked Questions

My client's fence panels keep blowing out in high winds — the posts are solid. What's wrong?

If the posts are solid but panels are blowing out, check: (1) panel clips or fixing method — clips can pull through the panel frame if the frame timber is wet and soft; (2) panel frame condition — joints that have opened allow racking and panel ejection; (3) wind exposure — hit-and-miss panels or close board will perform better on exposed sites. As an immediate fix, add additional panel clips or through-bolt the panel frame to the post face.

Can I treat pre-treated panels with additional treatment on delivery?

Yes. Factory-applied UC3 treatment is the base layer; an additional surface coat of fence treatment (water-based or oil-based) applied on delivery and annually thereafter significantly extends panel life. Treat the complete panel including the back face — one-sided treatment causes differential moisture absorption and board cupping.

How long do woven fence panels last compared to lapped?

Both are approximately equivalent in longevity because the board and frame materials are similar. Woven panels can be marginally more rigid than lapped panels (the weave pattern creates some triangulation), but the frame is typically the first failure point in either type. Quality differs far more between manufacturers than between panel types — a premium feather-edge panel outperforms both lapped and woven budget panels in longevity.

Regulations & Standards

• BS 1722-11 — Specification for wooden fence panels; construction, dimensions, and material requirements

• BS 8417 — Preservation of wood: code of practice; Use Class for panel components (UC3 above ground, UC4 for posts)

• Town and Country Planning Act 1990 / GPDO 2015 Schedule 2 Part 2 — Permitted Development heights for fences, gates, and trellis toppers

• BS 1722-11 Specification — BSI — British Standard for wooden fence panels

• Jacksons Fencing Panel Selection Guide — UK manufacturer's guide to panel types and installation

• Forest Research — Timber Treatment for Fencing — treatment specifications for fence components

• Planning Portal — Fences and Boundaries — Permitted Development guidance for trellis and panel heights

• close board fencing as a more durable alternative to panel fencing

• post setting requirements for panel fencing

• concrete post and gravel board systems for panel fences

• planning permission for fences and trellis toppers