Building for stability
The maximum height and minimum foundation width of free™standing walls are given for four wind exposure zones, shown on the map. By following the guidelines provided, stable freestanding walls can be constructed in most circumstances throughout the UK without the need to resort to formal design procedures. Safety margins are required for the development of these Standard Detail walls, and it is stressed that design methods (1) and rules (2) are available which may allow greater economy in use of materials or taller walls. The recommendations given here for height and foundation width should be taken as limits above which a design check is recommended to ensure stability. Greater heights are possible for more complex wall constructions and rules of thumb guidance for a range of these are given in GBG 19 (3).
Exclusions
The Standard Detail brickwork walls given here do not apply if any of the following exclusions apply, with the proposed wall being:
Where any of these conditions apply, these Standard Detail Walls should not be used - it is
not necessarily unsafe to build a wall - it is just that the assumptions made in calculating the wall
dimensions found here are not appropriate.
Under these circumstances you should seek the advice of a structural engineer, who will be able
to provide a bespoke designed solution.
Additional guidance These Standard Detail walls do not include stone walls, blockwork walls, complex plan walls, retaining walls or the construction of freestanding parapet walls on buildings. Further guidance on some of these forms of walling is available in:
However, you should seek structural advice before constructing walls with sunken panels or where brickwork or blockwork is to be combined with other materials such as wood panelling.
These, and other BRE documents, are available from Construction Research Communications Ltd (CRC) at 151 Rosebery Avenue, London, EC1R 4QX; e-mail crc@construct.emap.co.uk; and telephone 0171 - 505 - 6622, fax 0171 505 6606.
Procedure
The input data needed to obtain a Standard Detail wall are:
For each combination of input data, a dimensioned drawing of a Standard Detail wall will be generated, showing the required foundation width.
Where the combination of the required wall height and preferred wall thickness does not provide a safe solution, you will probably need to select a thicker wall.
1 Wall height
The height of the wall which will be used in the Standard Detail Wall is measured from the top
surface of the foundation to the top of any coping. Where no coping is present, this height is the
distance to the top of the brickwork.
2 Thickness of wall
Wall thickness given are in multiples of half bricks - either a half brick, a single brick, or 1½ bricks
thick. In the absence of other information, Where the wall is intended to be built to a different
thickness, the next smallest thickness should be used as the input data.
3 Wind exposure zones
The appropriate wind zone for the wall location can be found on the wind zone map. These wind
exposure zones are based on wind speed distributions across the UK, fitted as closely as possible
to the national grid, and you should select the correct wind zone on the basis of the location of the
proposed wall.
When determining the appropriate wind exposure zone for a series of walls, you must assess the
wind exposure zone for each wall, to ensure that the zone selected is appropriate for the location
of that particular wall.
4 Local exposure conditions
The local exposure conditions are used to allow for the differences in exposure which exist within
each of the exposure zones. You must choose either the 'sheltered' or 'exposed' condition, where:
Sheltered locations are typical urban areas, but possibly others, where there is considerable
local interruption of wind flow
Exposed locations are typical rural areas or others where there is a clear view over open country or where there is no local shelter from other buildings or trees.
Where there is any doubt over whether a site can be classed as 'sheltered', either seek specialist advice before proceeding or opt for the 'exposed' condition.
Where more than one wall is planned for a site, you must reassess the site exposure condition for
each wall - the conditions may change within a site, particularly if it is large.
Protection from vehicles
As a guide, provide a curb at a distance of 1 m, or a crash barrier at bumper height and at least 400 mm, from any freestanding wall which is to be built adjacent to an area which may be used by vehicles. If there is a high risk of damage by vehicles, consider building a reinforced wall.
Security and safety
A new wall may increase seclusion at ground level, but make sure that it will not provide a route for unwanted entry into the dwelling. Walls should not be positioned so that young children are tempted to climb on them or to use them as a route to other surfaces like flat roofs.
Planning considerations
You should check with the county surveyor if there are any local planning restrictions on wall height. Many councils have upper height maxima for walls in front of houses and between gardens. Trees should be planted at recommended distances from the wall foundations (see 7).
Piers
Piers of the sizes shown are recommended at the ends of all half brick and one brick walls. The piers described will be adequate for supporting a 1.2 m tall, 800 mm wide gate weighing no more than 10 kg. Seek structural advice if larger or heavier gates are to be supported on the wall.
Guidance on use of reinforced piers is given in GBG 19 (3).
Detailing at steps
Changes of level will require careful detailing of upper and lower dpcs and coping cappings. With cappings, plan changes of level so that adequate overhang of top dpc is possible at the step. In some cases the lower dpc may be easier to detail if movement joints are planned to coincide with steps.
Rendering
Where a render coat has been specified, make sure that the joints are raked back 10-12 mm to ensure a proper key. Render coats must not run over movement joints or bridge the lower dpc. Further advice on rendering is given in GBG 18(8).
Foundations
The choice of materials and their proportion is important if foundations are to be strong and durable. If the soil conditions are dry (water table always below the foundation level) a wide range of concrete mixes can be used (see 9, 10), including those based on ordinary Portland cement. The concrete mix will need more careful choice if the foundations are in wet or constantly damp soils; here the foundation will need to be resistant to any sulphate salts in the water and the choice of mix should be governed by concentration of salts present. You are advised to seek advice from the local Building Control Officer, especially in instances where a high water table coincides with sulphate-bearing clay soils. Always use clean tap water in preparing the mix. On soils contaminated by industrial waste, acids may be present; advice is available (10) on an appropriate acid-resisting concrete mix.
Masonry: bricks:
For reasons of stability, the density of the bricks used must be greater than 1200 kg/m³. Most clay,
calcium silicate and concrete bricks will be sufficiently dense. If in doubt, consult your supplier.
Clay bricks:
If the wall is to have a generous - 45 mm - overhang to the coping, a type MN or ML brick to BS
3921(11) should suffice for most conditions. Where greater frost resistance is required, type F
bricks should be used (see 12, which identifies relevant postcode areas).
| Below the low level dpc- | BRE recommends the use of type F bricks. |
| Above the high level dpc- | BRE recommends the use of type F bricks, type F capping bricks or type F engineering bricks - see the section on 'Cappings and copings'. |
Calcium silicate bricks:
Calcium silicate bricks to class 3, according to BS 187 (13), are suitable for use both above and below the dpc.
Mortar:
The high durability mortar mix shown below is normally suitable for all levels in the waIl (14).
Suggested mortar mix:
In wet locations consider using a designation (i) mortar (2) at and below the brick dpc level. Coarser sands (Type S, see 15) are recommended, particularly if using calcium silicate bricks. Sulphate-resisting Portland cement may be needed below the lower level dpc if building on wet soils.
Cappings and copings
Use cappings or copings to BS 4729 (16) or other copings to BS5642(17). Copings must be frost resistant and should shed rainwater clear of the wall. They are often specified in wetter regions but note that some rigid dpcs also deflect rainwater effectively and can substitute for a coping. Coping overhangs should be a minimum of 45 mm and be provided with a drip. In less exposed locations, or if frost resistant materials have been used throughout the wall, the need for protection against rainwater is not so great and smaller overhangs may be acceptable.
Cappings must be frost resistant. Galvanized or stainless steel metal straps can be used to strengthen ends of on-edge brick cappings but appearance and durability will be improved if special end capping bricks are used.
Copings and cappings must have a 'soft' waterproof joint above all movement joints. Where there is a risk of vandalism or of children climbing on walls, consider using an interlocking coping or capping system. For safety, copings/cappings at low level and up to about 1.5 m should preferably not have sharp edges, particularly if near walkways or play areas.
Some coping and capping options are set out in GBG 17(18).
Damp proof courses see BS 8215(19)
There are two main types of damp proof courses:
