This section is from the book "The Principles And Practice Of Modern House-Construction", by G. Lister Sutcliffe. Also available from Amazon: How Your House Works: A Visual Guide to Understanding & Maintaining Your Home.
The walls of houses are designed for a twofold purpose, namely, protection and support, or, to put it more fully, to protect the occupants and contents of the houses from those external influences which might act injuriously upon them, and to provide adequate support for floors and roof
It is only in lofty or heavy-laden buildings that the question of support needs much consideration. For ordinary brick or stone houses, a wall that is weather-proof will be amply strong enough to carry all the weight which will be put upon it. In exposed situations especially, the question of shelter or protection is practically the only one that requires attention. To fulfil this primary purpose, a wall must be proof against wind and rain, a bad conductor of heat, and durable.
The thickness of the walls has a considerable effect on the dryness and even temperature of a house, but the nature and quality of the materials constituting the walls, and the manner in which they are put together, are also of great importance. The thickness of a wall, in fact, must be varied according to the nature and quality of the materials and the manner of construction. Thus, rubble walls in which the stones are not laid in horizontal beds or courses, are usually specified to be one-third thicker than brick walls or squared-stone walls of the same height.
In order to put some check on the jerry-builder's love of flimsiness, building-regulations, prescribing inter alia the thickness of walls for buildings of various heights, have been adopted in all towns and cities. The regulations in force in London are somewhat intricate, but, speaking broadly, two-storied houses not more than 25 feet high must have walls not less than 8½ inches thick for the whole height, and three-storied houses must have walls 8½ inches thick for the highest story, and not less than 13 inches for the others. Walls from 40 to 50 high must be not less than 8½ inches thick for the top story, 17½ inches for the lowest, and 13 inches between. Walls from 50 to 60 feet high must be not less than 17½ inches thick for the two lowest stories, and 13 inches above. If the walls are unsupported by cross-walls, except at considerable distances, the thickness must be somewhat increased.
The thicknesses just given are for walls built of brick or squared stone, or of Portland-cement concrete properly laid in courses. Random rubble-walls must one-third thicker. In the case of hollow walls, there must be a wall on one side of the cavity of the full thickness prescril>ed by the Act.
Of course these regulations are for London only. The by-laws of other cities and towns differ considcrablv, but in a work of this kind it would be useless Attempting to note the different regulations, even of the largest towns. The by-laws in force in any locality must be carefully studied by the architect and builder before plans are drawn or work begun for any houses there. It will often, however, be advisable to adopt a greater thickness than the minimum allowed by the regulations; certainly an ordinary brick wall 8½ or 9 inches thick is little protection against cold and rain, especially in exposed situations.
The walls of houses are constructed of various materials - stone, brick, terracotta, concrete, mortar, wood, tiles, plaster, etc. But in most large towns and cities, the authorities insist on the walls being built of "brick, stone, or other hard and incombustible substances"; wood, valuable though it is as a non-conductor of heat, is too inflammable to be allowed for so important a part of a building as the walls. Of every kind of material there are different qualities - good, bad, and indifferent; and the durability, healthfulness, and comfort of a house depend largely on the proper selection of the several materials. Perhaps there is no part of an architects work more difficult or disagreeable than to decide as to the acceptance or rejection of materials which the builder has brought to the building-site.
It will be impossible here to enter with any degree of fulness into the varieties of every kind of material used in the construction of walls, but an attempt will be made to give briefly some useful information on the subject.
One general rule may be laid down: - Before adopting any particular material in a building, take care to examine its behaviour in one or more buildings in the immediate neighbourhood. This perhaps is particularly applicable to stone and book, but it will prove useful in other cases too.
And a second rule is: - Be chary of adopting new materials, or of using known materials in localities where they have not before been adopted. Had Sir Gilbert Scott acted upon a rule like this, he would not have specified Bath stone for the beautiful church at Haley Hill, in smoky Halifax, nor would the vicar and churchwardens have been called upon to "restore" the church within a few decades of its erection.
But while bearing this rule in mind, we must not run to the opposite extreme and resolutely ignore all new materials or new adaptations of old ones:
"Be not the first by whom the new are tried, Nor yet the last to lay the old aside".