A well-built brick garden wall will outlast the house it stands behind. A badly built one can lean, crack along the mortar joints and, in the worst case, fall on someone. The difference is rarely the bricklaying skill on the top; it is the planning, the foundation and the decision about how high the wall needs to be. This guide covers the sequence for a freestanding wall in a typical English garden: what the height rules say, how to think about foundations, which bricks and mortar suit outdoor work, and how to work out quantities before you place an order.

How high can you build?

For most houses in England, a new wall, fence or gate does not need planning permission if it would not exceed one metre in height when next to a road used by vehicles (or the footpath beside it), or two metres in height elsewhere, measured from ground level. The Planning Portal also notes that you cannot increase the height of an existing structure that already exceeds these limits without permission. The rights do not apply if the property is listed, if the wall is in the curtilage of a listed building, or where an Article 4 direction or a planning condition has removed them. In a conservation area you might need permission to take down a wall as well as to build one, and flats and maisonettes do not enjoy the same rights as houses. Wales, Scotland and Northern Ireland have their own planning rules, so confirm with your local planning authority if you are outside England.

Two practical points follow from this. First, check your deeds and any estate covenants, which can restrict boundary treatments even when planning law does not. Second, think about who owns the boundary. A wall built on the line, or foundations that cross it, can trigger the Party Wall etc. Act 1996, which has specific notice procedures when you build on or astride a boundary line; the government guidance explains when it applies. Building entirely on your own land, with foundations kept inside your boundary, is the simplest route, but get professional advice if you are unsure.

Do building regulations apply?

A freestanding garden wall is not usually controlled by the Building Regulations in England, but that does not make it exempt from the laws of physics or from a duty to be safe. Tall or exposed walls need engineering. As a rule of thumb that you should confirm locally, a wall approaching or exceeding one metre should be designed with piers or returns, and a wall of two metres is substantial structural work in its own right. Retaining walls, which hold back soil, are a different category entirely and often need calculations and sometimes building control involvement. If your wall will retain more than a small difference in level, treat it as an engineering job.

Choose the wall's thickness and form

A half-brick wall (one brick wide, around 102.5 mm thick) is tall enough for a low edging or a bed border, but it is flimsy as a freestanding feature taller than a few courses, because it has no resistance to sideways push. For a freestanding wall that is a boundary or screen, there are three usual approaches:

  • Solid one-brick wall (about 215 mm thick), laid in English or Flemish bond. Heavy and stable, using about twice the bricks per square metre.
  • Half-brick wall with piers. Piers, which are thicker columns at intervals, stiffen a thin wall. Spacing and size depend on the height and exposure, so ask a bricklayer or engineer, or check the guidance published by the brick manufacturers.
  • Cavity or double-skin wall. Rare for garden boundary walls; it costs more and has no great advantage over a solid wall.

Whatever you choose, include expansion joints in long runs, typically a vertical gap every 6 to 12 metres for clay brickwork depending on the manufacturer's recommendation, filled with a flexible sealant. Clay bricks expand a little over time as they take up moisture; long, rigid runs crack at weak points unless the movement is allowed for.

Foundations

The foundation is where most DIY walls fail. A wall transmits its weight and any wind load into the ground through a concrete strip. If that strip is too shallow, too narrow or sits on topsoil, the wall will move.

  • Depth. Dig below the topsoil and any loose or organic material onto firm subsoil. Frost, shrinking clay and tree roots all push depth requirements deeper. There is no single figure; conditions near large trees or on clay are a matter for a structural engineer or building control advice. Many builders dig at least 450 mm deep for a typical domestic wall, but treat that as a starting point to be confirmed, not a rule.
  • Width. Wider than the wall, so the load spreads. A common rule of thumb is a strip about two to three times the wall thickness, with at least 100 mm projecting each side of the wall.
  • Concrete thickness. Typically 150 mm or more of concrete in the bottom of the trench, to allow a few courses of bricks to be built below ground level up to the damp-proof course or the lowest visible course.
  • Level. Set steel pegs with their tops at the concrete level and screed to them, or use a laser level. A foundation that is level by eye is rarely level in practice.

Allow the concrete to harden before building on it, typically at least a day or two, longer in cold weather. The concrete volume calculator works for a strip as well as a slab: enter the length, width and depth of the trench fill.

Bricks and mortar for outdoor use

Garden walls are exposed on both faces, and the top is exposed to rain and freezing. Standard facing bricks are not all suitable. Brick specifications are given in BS EN 771-1 and the associated national guidance, which classify bricks by their frost resistance (F0, F1, F2 are the categories in the standard) and soluble salt content. For a freestanding wall, choose a brick sold as frost resistant and suitable for external walls and free-standing work, rather than a soft interior or "commons" brick. Ask your supplier to confirm this in writing or on the datasheet, because a brick that spalls (flakes off its face) after one winter cannot easily be replaced.

Mortar should be weaker than the brick, so that any movement cracks the replaceable mortar rather than the brick. Mortar for garden walls is commonly mixed from cement, building sand and a plasticiser, with the proportions set by the manufacturer of the plasticiser or the brick supplier. Typical figures quoted are one part cement to between four and six parts sand, with the richer mix for more exposed or higher walls, but follow the guidance on your products. Do not use a mix much stronger than the bricks need. Do not add washing-up liquid as a plasticiser, an old habit that entrains an uncontrolled amount of air.

Use a damp-proof course (DPC) near the base of the wall, at least 150 mm above finished ground level, to stop moisture rising into the brickwork and carrying salts that stain the faces. A coping on top, ideally overhanging the wall by 25 to 40 mm on each side with a drip groove or throating on the underside, protects the top course from saturation. Flat-topped brick-on-edge courses without a proper coping are a common cause of failure.

Working out quantities

A standard UK metric brick is 215 x 102.5 x 65 mm. With a 10 mm mortar joint, each brick occupies a face of (215 + 10) x (65 + 10) mm = 225 x 75 mm = 0.016875 square metres, so you need 1 / 0.016875 = 59.3, usually quoted as about 60 bricks per square metre for a half-brick wall in stretcher bond. A one-brick-thick wall roughly doubles that, to about 120 per square metre.

Worked example (illustrative numbers): a half-brick wall 6 m long and 0.9 m high, with a coping of separate coping stones.

  • Area = 6 x 0.9 = 5.4 square metres.
  • Bricks = 5.4 x 60 = 324. Add 5 to 10 percent for cuts and breakage: 324 x 1.10 = 356, so order about 360.
  • Mortar: the wet volume of mortar in a half-brick wall is about 0.018 cubic metres per square metre of wall. 5.4 x 0.018 = 0.097 cubic metres, and an allowance of 25 to 30 percent for waste and the bed under the foundation course raises the order to about 0.125 cubic metres of mixed mortar.

The brick wall quantities and mortar calculator does these sums and breaks the mortar down into cement and sand. Bricks are sold in packs, and batches vary in colour, so buy them all at once and a few spare, and mix bricks from several packs as you lay them.

Setting out and laying

  1. Dry-lay a course. Place the first course on the foundation without mortar, leaving 10 mm gaps, to check the layout and avoid awkward cuts at the ends.
  2. Build the ends first. Lay the corner or end leads a few courses high, checking plumb and level, and stretch a line between them to guide the courses in between.
  3. Bed the bricks. Spread a bed of mortar about 10 mm thick, furrow slightly, butter the end of each brick and tap it into position. Strike off surplus mortar with the trowel.
  4. Check constantly. A spirit level on every few bricks, plumb on every course at the ends. A small error repeated in each course becomes an obvious lean.
  5. Point the joints. When the mortar is thumb-print firm, rake or brush the joints to a consistent profile. A slightly recessed or weather-struck joint sheds water better than a flush finish that retains moisture.
  6. Limit the daily height. Do not build too many courses in a single day. Fresh mortar can squeeze out under the weight of new courses. A common guide is around 1.2 metres in one lift, but build lower in cold weather or with soft mixes.

Protect fresh work from rain and frost by covering the top with polythene or hessian, weighted down but not touching the faces. Avoid laying in freezing conditions. Brickwork that freezes before the mortar sets can be permanently damaged.

Piers, ties and openings

Gates need stronger piers than the wall, because the gate load acts at the end of the run. Do not hang a heavy gate on a half-brick wall end. If your wall includes a gate pier, use a one-brick-square or larger pier, built off a deeper, wider foundation, and think about embedding the hinge fixings during the build rather than drilling in later. Lintels over a gap, and any wall with a retained height difference, are structural elements that should be specified, not improvised.

Safety and cutting

Cutting bricks and concrete creates silica dust, which is harmful to lungs. Cut outdoors, with water suppression or extraction if possible, and wear a suitable dust mask rated for the job, eye protection and hearing protection. Wear gloves when handling mortar, as cement burns skin.

When to call a professional

Hire a qualified bricklayer or structural engineer if the wall will be higher than around one metre and free-standing, if it retains soil, if it adjoins a road or public space, if it sits near trees or on clay, or if it is on a boundary shared with a neighbour. This guide is general information and does not replace advice from your local planning authority or building control team, who can confirm what applies to your property.

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