Materials from which bricks are made.

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In this country there are very extensive areas of clay soil suitable for brickmaking. Clay differs quite widely in composition from place to place and the clay dug from one part of a field may well be quite different from that dug from another part of the same field. Clay is ground in mills, mixed with water to make it plastic and moulded, either by hand or machine, to the shape and size of a brick.

Bricks that are shaped and pressed by hand in a sanded wood mould and then dried and fired have a sandy texture, are irregular in shape and colour and are used as facing bricks due to the variety of their shape, colour and texture.

Machine made bricks are either hydraulically pressed in steel moulds or extruded as a continuous band of clay. The continuous band of clay, the section of which is the length and width of a brick, is cut into bricks by a wire frame. Bricks made this way are called ‘wire cuts’.

Brick and Block Walls.

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The majority of the walls of small buildings in this country are built of brick or block. The external walls of heated buildings, such as houses, are built as a cavity wall with an outer leaf of brick, a cavity and an inner leaf of concrete blocks. Internal walls and partitions are built, in the main, of concrete blocks.

The word brick is used to describe a small block of burned clay of such size that it can be conveniently held in one hand and is slightly longer than twice its width. Blocks made from sand and lime or concrete are manufactured in clay brick size and these are also called bricks. The great majority of bricks in use today are of clay.

The standard brick is 215 x 102.5 x 65 mm, as illustrated in Fig. 45, which with a 10mm mortar joint becomes 225 x 112.5 x 75mm. 

Fig. 45 Standard brick.

Resistance to the passage of sound - Materials construction.

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Sound is transmitted as airborne sound and impact sound. Airborne sound is generated as cyclical disturbances of air from, for example, a radio, that radiate from the source of the sound with diminishing intensity. The vibrations in the air caused by the sound source will set up vibrations in enclosing walls and floors which will cause vibrations of air on the opposite side of walls and floors.

Impact sound is caused by contact with a surface, as for example the slamming of a door or footsteps on a floor which set up vibrations in walls and floors that in turn cause vibrations of air around them that are heard as sound.

The most effective insulation against airborne sound is a dense barrier such as a solid wall which absorbs the energy of the airborne sound waves. The heavier and more dense the material of the wall the more effective it is in reducing sound. The Building Regulations require walls and floors to provide reasonable resistance to airborne sound between dwellings and between machine rooms, tank rooms, refuse chutes and habitable rooms. A solid wall, one brick thick, or a solid cavity wall plastered on both sides is generally considered to provide reasonable sound reduction between dwellings at a reasonable cost. The small reduction in sound transmission obtained by doubling the thickness of a wall is considered prohibitive in relation to cost.

For reasonable reduction of airborne sound between dwellings one above the other, a concrete floor is advisable.

The more dense the material the more readily it will transmit impact sound. A knock on a part of a rigid concrete frame may be heard some considerable distance away. Insulation against impact sound will therefore consist of some absorbent material that will act to cushion the impact, such as a carpet on a floor, or serve to interrupt the path of the sound, as for example the absorbent pads under a floating floor.

Noise generated in a room may be reflected from the walls and ceilings and build up to an uncomfortable intensity inside the room, particularly where the wall and ceiling surfaces are hard and smooth. To prevent the build-up of reflected sound some absorbent material should be applied to walls and ceilings, such as acoustic tiles or curtains, to absorb the energy of the sound waves.

Air changes.

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For general guidance a number of air changes per hour is recommended, depending on the activity common to rooms or spaces. One air change each hour for dwellings and three for kitchens and sanitary accommodation is recommended. The more frequent air changes for kitchen and sanitary accommodation is recommended to minimise condensation of moisture-laden, warm air on cold internal surfaces in those rooms.

Condensation - dwellings.

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Condensation is the effect of moisture from air collecting on a surface colder than the air, for example in a bathroom or kitchen where water from warm moisture-laden air condenses on to the cold surfaces of walls and glass. To minimise condensation, ventilation of the room to exchange moisture-laden air with drier outside air and good insulation of the inner face of the wall are required.

A consequence of the need for internal air change in buildings is that the heat source must be capable of warming the incoming air to maintain conditions of thermal comfort, and the more frequent the air change the greater the heat input needed. The major source of heat loss through walls is by window glass which is highly conductive to heat transfer. This heat loss can be reduced to some small extent by the use of double glazing. 

Most of the suppliers of double glazed windows provide one of the very effective air seals around all of the opening parts of their windows. These air seals are very effective in excluding the draughts of cold air that otherwise would penetrate the necessary gaps around opening windows and so serve to a large extent to reduce the heat loss associated with opening windows to an extent that they may reduce air changes to an uncomfortable level.

There is a fine balance between the need for air change and the expectations of thermal comfort that receives too little consideration in the design of windows.

Ventilation - comfort and good health in buildings.

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The sensation of comfort is highly subjective and depends on the age, activity and to a large extent on the expectations of the subject. The young ‘feel’ cold less than the old and someone engaged in heavy manual work has less need of heating than another engaged in sedentary work. It is possible to provide conditions of thermal comfort that suit the general expectations of those living or working in a building. None the less, some may ‘feel’ cold and others ‘feel’ hot.

For comfort and good health in buildings it is necessary to provide means of ventilation through air changes through windows or yentilators, that. can be controlled, depending on wind speed and direction and outside air temperature, to avoid the sensation of ‘stuffiness’ or cold associated with too infrequent or too frequent air changes respectively. As with heating, the sensation of stuffiness is highly subjective.

Calculation Methods for the SAP for dwellings.

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Three methods of calculating the figures necessary for the SAP for dwellings are proposed in Approved Document L. They are:

(1) an elemental method
(2) a target U value method
(3) an energy rating method.

In the elemental method standard U values for the exposed elements of the fabric of buildings are shown under two headings: (a) for dwellings with SAP ratings of 60 or less and (b) for those with SAP ratings over 60. The standard U values are 0.2 and 0.25 W/m2K for roofs, 0.45 W/m2K for exposed walls, 0.35 and 0.45 W/m2K for exposed floors and ground floors, 0.6 W/m2K for semi-exposed walls and floors and 3.0 and 3.3 W/m2K for windows, doors and rooflights, the two values being for headings (a) and (b), respectively. The basic allowance for the area of windows, doors and rooflights together is 225% of the total floor area. The area of windows, doors and rooflights, larger than those indicated by the percentage value, may be used providing there is a compensating improvement in the average U value by the use of glazing with a lower U value.

As it is unlikely that the SAP rating of the majority of new dwellings, complying with standard U values, will fall below 60, the over 60 rating values are the relevant ones.

The target U value method for dwellings is used to meet the requirement for conservation of fuel and power by relating a calculated average U value to a target U value, which it should not exceed. The average U value is the ratio of:

The total area of exposed floors, windows, doors, walls and roof and the standard U values in the elemental method are used to calculate the heat loss per degree. Where the calculated average U value exceeds the target U value it is necessary to improve the thermal resistance of walls, windows or roof either separately or together so that the average U value does not exceed the target U value. As an option, account may be taken of solar heat gains other than those allowed for in the equation on which the method is based. This method is based on the assumption of a boiler with an efficiency of at least 72%. Where a boiler with an efficiency of 85% is used the target U value may be increased by 10%. The use of the elemental or target U value methods of showing compliance does not give exemption from the requirement to give notice of an SAP rating.

The energy rating method is a calculation based on SAP which allows the use of any valid conservation measures. The calculation takes account of ventilation rate, fabric losses, water heating requirements and internal and solar heat gains.

The requirement for conservation of fuel and power will be met if the SAP energy rating for the dwelling, or each dwelling in a block of flats or converted building, is related to the floor area of the dwelling and ranges from 80 for dwellings with a floor area of 80 m2 or less to 85 for dwellings with a floor area of more than 120 m2.

As there is a requirement to complete the SAP worksheet to determine an SAP rating, which has to be notified to the local authority, whichever method of showing compliance is used the most practical and economic method of approach is to use the standard U values for SAP ratings over 60 set out in the elemental method in the initial stages of design, and then to complete the SAP worksheet at a later stage and make adjustments to the envelope insulation, windows and boiler efficiency as is thought sensible to achieve a high SAP rating.

For a description of the requirements for conservation of fuel and power for all buildings other than dwellings.