Many local councils have restrictions on the height of garden walls, although in most cases walls that do not form part of the house or an extension are unlikely to be the remit of Building Regulations. One exception to this general rule, however, is when the wall provides support to the foundations of a building.
Your local planning department will confirm the rules that apply in your area.
Retaining Garden Walls
Building Regulations are not usually required for walls constructed for landscaping, however, where the wall supports a large amount of earth you should take advice from a structural engineer to ensure they are built to the correct standard to prevent danger to the public.
If the retaining wall is built within 3.7 metres of any highway, the Highways Act 1980 requires the approval of the local authority. If the road is adopted, you will need the approval of the Highways Authority.
As a guide, retaining walls should be strong enough to resist the horizontal soil pressure that arises from the different ground levels.
Ground water can increase the pressure, potentially causing water to accumulate behind the structure, and this should be allowed a path of egress by adding drainage. Where necessary, movement joints and slip ties can be incorporated to prevent cracking and where a wall abuts a building.
Party Walls
In certain circumstances, garden walls may come under the terms of the Party Walls Act, particularly if the party wall is built on the land of more than one owner, and forms part of a building or where it is sited on one owner’s land but is used by other owners to separate their buildings.
A Chartered Surveyor will give advice on party wall matters, including garden walls. Whether or not the duty of care for maintenance of garden walls built on a boundary is the responsibility of one owner or the other is not straightforward, and reference should be made to HM Land Registry and the title deeds of the properties. A Chartered Surveyor will make an assessment which can be used to assist a property owner reach agreement should no duty of care be specified.
Safety of Garden Walls
To check whether repairs are necessary, or if a wall needs rebuilding, garden and boundary walls should be inspected from time to time. Garden walls are among the most common forms of masonry to collapse, and they are one of the commonest causes of death by falling masonry. Your insurance may not cover you if the wall has been neglected.
Over the years, masonry walls may be affected by:
- general deterioration and ageing;
- an increase in wind load or driving rain, if a nearby wall is taken down;
- the felling of nearby trees or planting new trees close to the wall;
- changes leading to greater risk of damage from traffic;
- alterations, including additions to walls or the removal of parts of the wall e.g. for a new gateway;
- changes to the water table equilibrium.
Things to check include:
- Is the surface of the brickwork crumbling away? If the damage is restricted to a few bricks this may not be serious, but walls can be weakened by general crumbling across either face.
- Is the mortar pointing in good condition? If the hard surface layer can be picked out from the joint, or if the mortar can easily be scraped out, perhaps with a door key, then this is a good indication that the wall may need repointing.
- Is there a tree near the wall? As trees mature, there is a risk of the wall being damaged by roots, and from falling branches. Damaged sections may need to be re-built, perhaps with bridges incorporated to carry the wall over the roots. Removal of mature trees can also lead to problems as soil accumulates more moisture and expands. Dead tree roots can also collapse, undermining the wall’s foundations.
- Is the wall upright? Walls lean for a variety of reasons, sometimes because of failure below ground caused by tree roots, cracked drains, frost damage to the foundations or inadequate foundations. If your wall leans to an extent that it could present a danger e.g. more than 30mm (half brick wall), 70mm (single brick wall) or 100mm (brick and a half wall) you should seek expert advice, which may also involve checking the wall foundations.
- Is the wall thick enough for its height? The table below gives guidance on how high walls should be in different parts of the UK relative to their thickness. You should seek expert advice if your wall exceeds the recommended height, or where this guidance is inapplicable e.g walls incorporating piers, supporting heavy gates or retaining soil.
- Some climbing plants, such as ivy, can damage walls if growth is unchecked. Consider cutting them back and supporting regrowth with trellis, clear of the wall.
- Is the top of the wall firmly attached? Brick or concrete copings may be loose or the wall may have horizontal cracks in the brickwork a few courses down, possibly from frost damage. Loose or damaged masonry near the top of the wall will need to be rebuilt.
- Has the wall been damaged by traffic? Minor scratch marks or scoring of the surface may hide more significant cracks. Piers at vehicular entrances may have been dislodged by impact and be unsafe; in such cases, they should be rebuilt.
- Are there any cracks in the wall? Hairline cracks (0-2mm across) are common in walls and may not be an indication of serious problems. For wider cracks seek expert advice – some may indicate a need for partial or complete rebuilding. Seek advice on any horizontal cracks which pass right through a wall or which are close to piers or gates. Repointing cracks can lead to problems. Never repoint without first establishing the cause of the cracking.
Height of Garden Walls
Safe heights for walls of different thicknesses (Government guidelines)
| Zone 1 | Zone 2 | Zone 3 | Zone 4 | ||||
| *Wall Thickness | Max. Height | *Wall Thickness | Max. Height | *Wall Thickness | Max Height | * Wall Thickness | Max. Height |
| ½ Brick¹ | 525mm | ½ Brick ¹ | 450mm | ½ Brick ¹ | 400mm | ½ Brick ¹ | 375mm |
| 1 Brick ² | 1450mm | 1 Brick ² | 1300mm | 1 Brick ² | 1175mm | 1 Brick ² | 1075mm |
| 1½ Brick ³ | 2400mm | 1½ Brick ³ | 2175mm | 1½ Brick ³ | 2000mm | 1½ Brick ³ | 1825mm |
| 100mm Block | 450mm | 100mm Block | 400mm | 100mm Block | 350mm | 100mm Block | 325mm |
| 200mm Block | 1050mm | 200mm Block | 925mm | 200mm Block | 850mm | 200mm Block | 775mm |
| 300mm Block | 2000mm | 300mm Block | 1825mm | 300mm Block | 1650mm | 300mm Block | 1525mm |
¹ = 100mm; ² = 215mm; ³ = 323mm.
Certain conditions may override this guidance, including where the wall is:
- Adjacent to a vehicle access area or public right of way;
- Where busy traffic areas are likely;
- Close to a building over four storeys high, that is closer than a distance equal to the height of the building;
- On the crest of a hill or where the slope of the ground is greater than 1:10;
- Near an extensive hill or mountain range;
- Intended to support a large gate or door;
- Where the sub soil is soft, for instance, soft clay or peat, or the ground unstable;
- Where the difference in ground level between each side of the wall exceeds twice the wall thickness.
For more advice on all of these matters contact www.PropertySurveying.co.uk