Can I add trellis to the top of my fence?

Topping a fence with trellis is one of the most common ways people try to add privacy. It is perfectly legal in principle, but only if you understand that the trellis is part of the fence's measured height, not a bonus you can stack on top.

Trellis is part of the fence's height

The most important thing to understand is how height is measured. Permitted development limits apply to the entire structure on the boundary, from the ground to its highest point. Trellis fixed to the top of a fence is part of that structure, so it adds to the measured height in exactly the same way a taller panel would.

This means there is no special trellis allowance. The widely repeated belief that you can add, say, 30 cm of trellis on top of a 2 metre fence because 'trellis does not count' is simply wrong. A 2 metre fence with a 30 cm trellis topper is a 2.3 metre structure, and 2.3 metres is over the 2 metre limit. To stay within permitted development, the total of fence plus trellis must not exceed the applicable limit.

Working out whether your trellis is allowed

The arithmetic is straightforward once you know the limit for your boundary:

• Boundary not next to a road: fence plus trellis must total 2 metres or less. So a 1.7 metre fence can take up to 0.3 metres of trellis; a 1.5 metre fence can take up to 0.5 metres.
• Boundary next to a highway used by vehicles: the total must be 1 metre or less, so there is very little room for trellis on a roadside fence.

Measure from the natural ground level on the higher side of the fence to the top of the trellis. Remember to include posts and any gravel board if they sit higher than the panel. If the total comes in at or under the limit, you can add the trellis without permission. If it goes over, you need planning permission for the extra height.

How much trellis a fence can take within the 2 metre limit. Source: Planning Portal permitted development guidance.

If the fence belongs to your neighbour

Height is only half the question. If the fence is not yours, you cannot attach trellis to it without the owner's permission, regardless of height. The fence is their property, and fixing trellis, brackets or battens to it is interfering with their property, which can amount to trespass to goods. Trellis also adds wind load and pierces the timber with fixings, accelerating wear, which is exactly why owners object.

If you want trellis but the fence is the neighbour's, the clean solution is to put up your own trellis on your own posts, just inside your boundary. That keeps the fixings on your land and the structure under your control, while still respecting the overall height limit measured on your side.

Adding privacy without breaching the limit

If your fence is already at or near 2 metres and you want more screening, there are lawful alternatives to a topper that would breach the height limit:

• Plants and hedging: there is no planning height limit on most hedges (though anti-social-behaviour rules can address a hedge that becomes an unreasonable nuisance to a neighbour's light). A hedge or climbers grown on your own supports can add height and screening that a hard structure could not.
• Free-standing screens set back from the boundary: a screen positioned a little inside your garden, rather than fixed on the boundary, is assessed differently and can sometimes give privacy without breaching the boundary fence limit, though tall structures may still need permission depending on siting.
• Apply for permission: if you genuinely need a taller boundary, a planning application for the extra height is the proper route, decided on the impact on neighbours and the street scene.

Pergolas, gazebos and other garden structures have their own permitted development rules, so a tall planted screen or a structure set away from the boundary can achieve privacy where a boundary topper would not.

What happens if the total is too high

If you add trellis that pushes the boundary over the limit without permission, the council can take planning enforcement action, which may require you to reduce the height or remove the trellis. Enforcement is usually triggered by a neighbour complaint, so an overheight topper that blocks a neighbour's light or view is more likely to be reported. The safe approach is to do the sums first, keep fence plus trellis within the 2 metre (or 1 metre roadside) limit, and apply for permission before going taller. If the fence is the neighbour's, get their consent before attaching anything, or build your own supports just inside your boundary instead.

Frequently asked questions

Sources & further reading

• Planning Portal — fences, gates and garden walls
• GOV.UK — when you need planning permission
• GOV.UK — high hedges complaints

Figures on this page are typical UK ranges drawn from published sources and depend on your specific garden. They are guidance, not a quotation.