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Walls may be divided into two types:
a Load-bearing walls which support loads from floors and roof in addition to their own weight and which resist side pressure from wind and, in some cases, from stored material or objects within the building,
b non-load-bearing walls which carry no floor or roof loads. Each type may be further divided into external or enclosing walls, and internal dividing walls. The term partition is applied to walls, either load-bearing or non-loadbearing, dividing the space within a building into rooms.
Good quality walls provide strength and stability, weather resistance, fire resistance, thermal insulation and sound insulation.
Types of Building Walls
There are various ways to construct a wall and many different materials can be used, but they can be divided into four main groups.
Masonry wall, in which the wall is built of individual blocks of materials such as brick, clay or concrete blocks, or stone, usually in horizontal courses bonded together with some form of mortar. Several of the earth derived products, either air dried or fired, are reasonable in cost and well suited to the climate.
Monolithic wall, in which the wall is built of a material placed in forms during the construction. The traditional earth wall and the modern concrete wall are examples. The earth walls are inexpensive and durable if placed on a good foundation and protected from rain by a rendering or wide roof overhangs.
Frame wall, in which the wall is constructed as a frame of relatively small members, usually of timber, at close intervals which together with facing or sheething on one or both sides form a load-bearing system. Offcuts are a lowcost material to use for a frame wall covering.
Membrane wall, in which the wall is constructed as a sandwich of two thin skins or sheets of reinforced plastic, metal, asbestos-cement or other suitable material bonded to a core of foamed plastic to produce a thin wall element of high strength and low weight.
Another form of construction adapted for framed or earth buildings consists of relatively light sheeting secured to the face of the wall to form the enclosed element. These are generally termed 'claddings'.
Factors which will determine the type of wall to be used are:
The height of walls should allow people to walk freely and work in a room without knocking their heads on the ceiling, beams etc. In dwelling houses with ceilings is 2.4m a suitable height. Low roofs or ceilings in a house create a depressing atmosphere and tend to make the rooms warmer in hot weather.
Masonry Walls
Apart from certain forms of stone walling, all masonry consists of rectangular units built up in horizontal layers called courses. The units are laid up with mortar in specific patterns called bonding in order to spread the loads and resist overturning and in the case of thicker walls, buckling.
The material in the masonry units can be mud or adobe bricks, burnt clay bricks, soil blocks (stabilized or unstabilized), concrete blocks, stone blocks or rubble. Blocks can be solid or hollow.
Figure 5.18 Examples showing why bonding is necessary.
Figure 5.19 English and Flemish bonding of brick walls.
Bricks
In brickwork, those bricks laid lengthwise in the wall are called stretchers and the course in which they occur, a stretching course. Bricks laid across the wall thickness are called headers and the course in which they occur, a heading course.
Bricks may be arranged in a wide variety of ways to produce a satisfactory bond and each arrangement is identified by the pattern of headers and stretchers on the face of the wall. These patterns vary in appearance resulting in characteristic 'textures' in the wall surfaces, and a particular bond may be used for its surface pattern rather than for its strength properties. In order to maintain bond it is necessary at some points to use bricks cut in various ways, each of which has a technical name according to the way it is cut.
The simplest arrangements, or 'bonds' as they are called, are stretching bond and heading bond. In the former, each course consists entirely of stretchers laid as in Figure 5.20 and is only suitable for half-brick walls such as partitions, facing for block walls and the leaves of cavity walls. Thicker walls built entirely with stretchers are likely to buckle as shown in Figure 5.18. The heading bond is ordinarily used only for curved walls.
The two bonds most commonly used for walls one brick and over in thickness are known as English bond and Flemish bond. A 'one-brick thickness' is equal to the length of the brick. These bonds incorporate both headers and stretchers in the wall which are arranged with a header placed centrally over each stretcher in the course below in order to achieve a bond and minimize straight joints. In both bonds 120 bricks of standard size are required per m˛ of 23cm wall. This figure allows for 1 5 to 20% breakage and 1cm mortar joints. Figure 5.19 illustrates English and Flemish bonding.
Bricks are sometimes used in the construction of cavity walls since the airspace improves the thermal resistance and the resistance to rain penetration compared to a solid wall of the same thickness. Such a wall is usually built up with an inner and outer leaf in a stretching bond, leaving a space or cavity of 50 to 90mm between the leaves. The two leaves are connected by metal wall ties spaced 900mm horizontally and 450mm vertically as shown in Figure 5.20.
Figure 5.20 Brick cavity wall.
Concrete Blocks
Much of the procedure for the construction of concrete block walls has been discussed under the heading 'Foundations'. However, there are a few additional factors to be considered.
It is best to work with dry, well-cured blocks to reduce shrinking and cracking in the wall to a minimum. Except at quoins (corners), load-bearing concrete block walls should not be bonded at junctions as in brick and stone masonry. At junctions one wall should butt against the face of the other to form a vertical joint which allows for movement in the walls and thus controls cracking. Where lateral support must be provided by an intersecting wall, the two can be tied together by 5mm x 30mm metal ties with split ends, spaced vertically at intervals of about 1 200mm. Expansion joints should be allowed at intervals not exceeding 2 1/2 times the wall height. The two sections of wall must be keyed together or stabilized by overlapping jamb blocks as shown in Figure 5.21. The joints are sealed with flexible mastic to keep water from penetrating the wall.
Figure 5.21 Lateral support for walls at expansion joints.
Many walls in the tropics are required to let in light and air while acting as sun-breakers. To meet this need, perforated walls are popular and are designed in a variety of patterns, some load bearing, others of light construction. Hollow concrete blocks may be used to good effect for this purpose. Horizontal or vertical slabs of reinforced concrete (r.c. slots) can be used to act as sunbreakers. These are usually built at an inclined angle in order to obtain maximum shelter from the sun.
Stones
Quarried stone blocks, either rough or dressed to a smooth surface are laid in the same way as concrete or stabilized soil blocks. Random rubble walls are built using stones of random size and shape as they are found or come from the quarry. Walls using laminated varieties of stone which split easily to reasonably straight faces of random size are called squared rubble walling.
Figure 5.22 Block walls for ventilation.
In these walls, as in all masonry, longitudinal bond is achieved by overlapping stones in adjacent courses, but the amount of overlap varies because the stones vary in size. Since rubble walls are essentially built as two skins with the irregular space between solidly filled with rubble material (small stones), transverse bond or tie is ensured by the use of long header stones known as bonders. These extend not more than three-quarters through the wall thickness to avoid the passage of moisture to the inner face of the wall and at least one is required for each m˛ of wall face. Large stones, reasonably square in shape or roughly squared, are used for corners and the jambs of door and window openings to obtain increased strength and stability at these points.
Random rubble walls may be built as uncoursed walling in which no attempt is made to line the stones into horizontal courses, or it may be brought to courses in which the stones are roughly levelled at 300mm to 450mm intervals to form courses varying in depth with the quoin and jamb stones.
Rough squaring of the stones has the effect of increasing the stability of the wall and improving its weather resistance since the stones bed together more closely, the joints are thinner, and therefore there is less shrinkage in the joint mortar. External load-bearing stone walls should be at least 300mm thick for one-story buildings.
Openings in Masonry Walls
Openings in masonry walls are required for doors and windows. The width of opening, height of the wall above the opening and strength of the wall on either side of the opening are major design factors. They are particularly important where there are many openings that are quite close together in a wall.
The support over an opening may be a lintel of wood, steel or reinforced concrete or it may be an arch constructed of masonry units similar to or the same as used in the adjoining wall. Lintels impose only vertical loads on the adjoining sections of walls and are themselves subjected to bending and shear loads and compression loads at their support points. Concrete lintels may either be cast in place or prefabricated and installed as the wall is constructed.
Figure 5.23 Coursed and uncoursed random rubble walls.
Arches are subjected to the same bending and shear forces, but in addition there are thrust forces against both the arch and the abutting sections of the wall.
It is not difficult to determine loads and choose a wood or steel lintel to install, or to design the reinforcing for a concrete lintel. However, the design of an arch always involves assumptions and then verification of those assumptions.
Lintels made of wood are suitable for light loads and short spans. Timber pressure treated with a preservative should be used.
Steel angles are suitable for small openings and Table 5.8 presents size, span and load information for several sizes. Larger spans require universal section 1 - beams and a specific design analysis. Steel lintels should be protected from corrosion with two or more coats of paint.
Table 5.8 Allowable Uniformly Distributed Loads on Steel Angle Lintels ( kg)
| Angle size, mm | Weight | Safe load (kg) at Span length, (m) | ||||
| V x H x Th | kg/m | 1 | 1.5 | 2 | 2.5 | 3 |
| 90 x 90 x 8 | 10.7 | 1830 | 1200 | 900 | 710 | |
| 125 x 90 x 8 | 13.0 | 3500 | 2350 | 1760 | 1420 | 1150 |
| 125 x 90 x 13 | 20.3 | 5530 | 3700 | 2760 | 2220 | 1850 |
| 125 x 102 x 10 | 18.3 | 6100 | 4060 | 3050 | 2440 | 2032 |
V = vertical leg. H = horizontal leg, Th = thickness
Reinforced concrete is a very common material used for lintels.
Concrete lintels are made of 1:2:4 concrete mix (with an ultimate strength of 13.8N/mm˛) and are normally reinforced with one steel bar for each 100mm of width. For reasonably short spans over door and window openings, the 'arching' action of normal well-bonded bricks or blocks due to the overlapping of the units may be taken into account. It may be assumed that the lintel will carry only that part of the wall enclosed by a 45° equilateral triangle with the lintel as its base. For wide spans, an angle of 60° is used. For spans up to 3m the sizes of lintels and the number and sizes of reinforcement bars shown in Table 5.9 may be used. The steel bars should be covered with 40mm of concrete and the bearings on the wall should be preferably 200mm or at least equal to the depth of the lintel. Lintels with a span greater than 3m should be designed for the specific situation.
Long-span concrete lintels may be cast in situ in formwork erected at the head of the opening. However, precasting is usually adopted where suitable lifting tackle or a crane is available to hoist the lintel into position or where it is light enough to be put into position by two men.
Stone is generally used as a facing for a steel or concrete lintel. Unless reinforced with mild steel bars or mesh, brick lintels are only suitable for short spans up to Im, but like stone, bricks are also used as a facing for a steel or concrete lintel.
The arch is a substructure used to span an opening with components smaller in size than the width of the opening. It consists of blocks which mutually support each other over the opening between the abutments on each side. It exerts a downward and outward thrust on the abutments which must be strong enough to ensure stability of the arch.
Jointing and Pointing
Jointing and pointing are terms used for the finishing given to both the vertical and horizontal joints in masonry, irrespective of whether the wall is made of brick, block or stone construction. Jointing is the finish given to the joints as the work proceeds. Painting is the finish given to the joints by raking out the mortar to a depth of approximately 20mm and refilling the face with a hard-setting cement mortar which can have a colour additive. This process can be applied to both new and old buildings. Typical examples of jointing and pointing are given in Figure 5.25.
Figure 5.24 Openings in masonry walls.
| Size of Lintel(mm) | Clear Span | Bottom Reinforcement | ||
| H | W | m | Number of bars | Size of bars |
| 150 | 200 | <2.0 | 2 | 10mm, round, deformed |
| 200 | 200 | 2.0- 2.5 | 2 | 10mm, round, deformed |
| 200 | 200 | 2.5 - 3.0 | 2 | 16mm, round, deformed |
| Split Lintels with Wall Load Only | ||||
| 150 | 200 | <2.0 | 1 each | 10mm, round, deformed |
| 200 | 200 | 2.0-2.5 | 1 each | 10mm, round, deformed |
| 200 | 200 | 2.5 -3.0 | 1 each | 16mm, round, deformed |
Safe bearing at each end, 200mm
Figure 5.25 Examples of jointing and pointing.
Monolithic Earth Walls
Earth wall construction is widely used because it is an inexpensive building method and materials are usually abundantly available locally. Because the earth wall is the only type many people can afford, it is worthwhile to employ methods that will improve its durability. It has been found that susceptibility to rainfall erosion and general loss of stability through high moisture can be eliminated if simple procedures are followed during site selection, building construction and maintenance.
Earth walls are mainly affected by:
For one-story earth walled houses, structural considerations are less important because of the light roofing generally used. A badly designed or constructed earth-walled building may crack or distort, but sudden collapse is unlikely. Durability, not strength, is the main problem and keeping the walls dry after construction is the basic solution. Methods of stabilizing earth can be found in Chapter 3.
Key factors for improving the durability of earth-walled buildings include:
The material soil can be used in many ways for wall construction. Hand - rammed or machine - compacted, stabilized soil blocks and sun-dried mud (adobe) bricks are used in the same mannor as masonry units made of other materials. While masonry constructions have already been described, it should be noted that the somewhat poorer strength properties and durability of soil blocks and adobe bricks may make them less suitable for some types of construction, e.g. foundation walls. Special care must be taken when designing lintel abutments to ensure that the bearing stresses are kept within the allowable.
Rammed Earth Walls
A method for the construction of a monolithic earth wall is shown in Figure 5.26. The use of soil mixed with a suitable stabilizer at a proper ratio will increase the strength and durability of the wall provided the wall is properly cured. However, the single most important factor when constructing a rammed earth wall (using stabilized or natural soil) is perhaps thorough compaction of each layer of soil as it is filled in the mould. the formwork must be strong enough to resist the lateral forces exerted by the soil during this operation. The distance between lateral supports (cross walls etc.) should not exceed 4m for a 300mm thick rammed earth wall.
Figure 5.26 Construction of a rammed-earth wall
Finish the foundation wall with a sand/cement mortar cap. Supported on horizontal brackets running across the wall - a mould is constructed. The brackets, as well as, draw wires above the mould act as ties and must, together with the rest of the mould be sufficiently strong to resist the pressure of the earth during the ramming operations. Fill the earth in thin layers and compact thoroughly before the next layer is placed. After the mould has been filled, it is removed and placed on top of the already finished wall. While the mould is only 500 to 700mm deep, it will be moved several times before the finished height of the wall is reached. Notching of the sections will increase the stability of the wall. A work force that is large enough to allow several operations, such as soil preparation, transport, filling and ramming, to go on simultaniously will ensure swift construction.
Gliding Formwork for Rammed-earth Walls
The foundation wall is built to 5Ocm above the ground level with stones and lime mortar. Reinforcement in the walls consists of poles or bamboo which are set in the trench when the stones of the foundation wall are laid. The earth panel in the gliding formwork is tamped layer after layer until the form is full. The form is then moved and a new panel started. Finally the upper ring beam is tied to the reinforcement sticks. After finishing the panels, the joints are filled with earth mortar.
Mud and Pole Walls
The construction of mud and pole walls is dealt with at the end of Section Earth as Building Material along with some other types of mud wall constructions. A pole frame wall can be built with either thick earth construction (25cm or more) or thin earth cladding (10cm or less). While soil block walls and rammed earth walls usually are superior to mud and pole wall, this should only be used when a supply of durable poles is available and the soil is not suitable for block making. Regardless of the type of wall, the basis of all improvement is to keep the wall dry after construction.
Install a dampproof course on top of the foundation wall, about 50cm above ground level. Pre-fabricate ladders out of green bamboo or wooden poles that are about 5cm diameter. The outside wooden or split bamboo battens are nailed or tied to the ladders as the soil is filled in successive layers. The corners must be braced diagonally. Earthquack resistance is improved by securing the base frame to the foundation with a layer of lime or cement soil mortar.
Figure 5.27 Construction of a rammed-earth wolf with a gliding form.
Figure 5.28 Construction of a mud and pole wall.
Framed Walls
Frame walls consist of vertical timber members called studs framed between horizontal members at the top and bottom. The top member is called a plate and the bottom member a sole or sill. Simple butt joints are used which are end-nailed or toe-nailed. The frame is, therefore, not very rigid and requires bracing in order to provide adequate stiffness.
Diagonal braces can be used for this purpose, but a common method which is quicker and cheaper, is to use building board or plywood sheething to stiffen the structure. The studs are commonly spaced on 400 or 600mm centres which is related to the standard 1200mm width of many types of building boards used for sheathing. Since the load-bearing members of this type of wall are wood, it is not recommended for termite areas, especially if both faces of the frame are finished or covered, thus making it difficult to detect a termite attack.
Frame construction using timber must be raised out of contact with ground moisture and protected from termites. This is accomplished by erecting it on a base wall or foundation beam rising to a damp-proof course, or on the edge of a concrete slab floor. As a base for the whole structure a sill is set and carefully levelled on the dampproof course and securely anchored to the foundation. To maintain the effectiveness of the dampproof course it must be sealed carefully at all bolt positions. A continuous termite shield should be installed between the damp-proof course and the sill and great care taken to seal around the holes required for the anchor bolts. The sill plate may be 100mm by 50mm when fixed to a concrete base, but should be increased in width to 150mm on a brick base wall.
Instead of timber, bamboo or round wooden poles can be used as studs which are then clad with bamboo mats, reed mats, grass, palm leaves etc. A further alternative is to fix mats to the studs and then plaster the mats with ;cement plaster or other material. Some structures of this type have a short life due to damage by fungi and termites. They are also difficult to keep clean and the risk of fire is great. Figure 5.30 gives brief information on bamboo wall panels which can be made by skilled craftsmen.
Figure 5.29 Frame wall construction.
Facings and Claddings
Facings and claddings refer to panels or other materials that are applied as external coverings on walls for protection from the elements or for decorative effects. Facings or claddings are particularly useful for protecting and improving the appearance of the walls of earth structures which by themselves may be eroded by rain and become quite unsightly.
Facings generally have little or no structural strength and must be attached to a smooth continuous surface. Plaster or small size tiles are examples.
Cladding differs from facing in that the materials have some structural strength and are able to bridge the gaps between the battens or furring strips on which they are mounted. Various shingles, larger size tiles, both vertical and horizontal timber siding and building boards such as plywood and asbestos-cement board are suitable for cladding. Corrugated steel roofing is also satisfactory. The cladding materials must be able to transfer wind loads to the building structure and to absorb some abuse from people and animals. The spacing of the furring strips will influence the resistance of the cladding to these forces.
The spacings for shingles and tiles is determined by the length of the units. The spacing for horizontal timber siding should ordinarily be about 400mm, while vertical timber siding can safely bridge 600mm. Plywood of at least 12mm thickness can bridge 1200mm edge to edge if supported at 800mm intervals in the other direction.
Metal roofing used as cladding can be mounted on furring strips spaced 600mm apart. It is common for manufacturers of building materials to provide installation instructions, including the frequency of support members.
