MANY important details relating to house construction have already been dealt with in the previous chapters; the building itself and its site have now to be considered.

BUILDING-SITES.

The site for a house is often selected without regard to its suitability from a health point of view. Speculative builders naturally take no interest in the question, landowners are only too anxious to avail themselves of the extra price offered for building-sites, and, as a rule, the public either under-estimate or are ignorant of the important influence that locality and soil have on health.

The important considerations in selecting a site are-dryness, warmth, light, and air, and, as a rule, dryness and warmth go together, as do light and air.

The dryness of a site is mainly dependent upon the facility with which rain can pass off or through the soil, and the distance from the surface of the subsoil water (see p. 13). It follows, therefore, that flat and non-porous land, or land which, though porous, has an impervious stratum immediately underneath, is not desirable as a building-site. A gravelly soil, of considerable depth, and on a slight slope, is probably the best site that can be selected from this point of view, for not only does it afford facilities for natural drainage, but, by reason of its depth, the subsoil water is a long way from the surface. On the other hand, although the surface be of sand or gravel, if within a few feet there is a bed of clay, the pervious upper layer simply acts as a sponge, and absorbs the water which lies on the impervious bed immediately underneath; such a site, therefore, is not a favourable one, although it may be much improved by subsoil drainage.

Impermeable rocks, as regards dryness, are healthy, as the water readily runs off them, but in country districts the difficulty of obtaining water in many cases militates against such

sites.

Chalk soil is dry and healthy; so is sandstone, provided (for the reason given in the case of gravel) it is of considerable depth and uninterrupted by clay.

Clay and marl, but especially the former, are damp, and unless thoroughly drained are not desirable for building-sites.

The connection between damp surroundings and phthisis has already been referred to (p. 3), and it is probable that the prevalence of other lung diseases, as well as rheumatism, neuralgia, and throat affections, is influenced by damp.

Peat land, and all soils which contain much vegetable or animal matter, are unhealthy.

Made soils ought to be shunned, owing to the amount of organic matter they are likely to contain, which will exist in a state of putrefaction for years, and render the air surrounding the house impure.

The ground air—that is, the air which is intermixed with the soil from its surface down to the level of the subsoil or ground water-is continually being discharged into the atmosphere, owing, among other causes, to its displacement by the rainfall. This is the reason why it is important that the soil on which houses are built should, as far as possible, be free from vegetable and animal matter. To the presence of such decaying matter certain diseases are largely attributed. Most authorities are now agreed that typhoid fever, infantile diarrhoea, and diphtheria are intimately connected with ground effluvia from soils which have been polluted owing to faulty drainage, cesspools, &c.; hence the importance of guarding against any such risks of pollution of the ground surrounding houses as well as their actual sites.

The warmth of a site, other things being equal, is influ enced by the nature of the soil and the degree of moisture it contains.

The power of absorbing heat differs in different soils, as has been proved by Schübler, who has estimated it as follows, assuming 100 as the standard :—

These figures indicate how greatly superior the absorbing power of sand is as compared with clay, and, consequently, how much warmer it is as a site. Again, the evaporation from the surface (see p. 12) is greater the damper it is, and as loss of heat results from evaporation, consequently a damp site is colder than a dry one.

It follows from what has been said that, in selecting a site for a house, preference must be given to one which is dry, and if there is no alternative to building on a damp site, it is imperative that it should first be drained. Attention should be paid to encouraging the natural drainage, by removing obstructions that may exist to the free flow of the streams in the neighbourhood, and thus lowering the subsoil water. The measures to be adopted against damp as regards the building itself will be considered later.

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The two important requirements, light and air, are to be secured, as regards the first, by selecting a southerly or southwesterly aspect, and as regards the second, a site well removed from other buildings, and not closely surrounded by trees. is not always possible in towns to obtain the advantages in this respect afforded by the country, but the more breathing space that can be provided the better, and to insure attention to this, all urban authorities should adopt bye-laws defining the limits beyond which buildings shall not extend (see Appendix).

BUILDING MATERIALS.

Bricks of good quality should be heavy and hard, and when knocked one against the other, they ought to give a clear, ringing sound. Soft bricks are more absorbent than hard ones, consequently walls built of the former are more likely to be damp and cold. Frost also has a crumbling effect upon them. The usual size of bricks is 9 inches in length, by 4 inches in width, and 3 inches in thickness.

The quality of bricks, as of other materials used in house building, varies, and upon it depends, in a great measure, the health and comfort of the inmates. In certain districts the clay is peculiarly well suited for brick-making, and there the chance of bad bricks being used is much less than in other districts, where, owing to the quality of the clay, the "tempering" process entails greater labour. An important part in the process of brick-making is the burning. The heat has to be raised gradually up to a certain point, at which it should be maintained,

without variation, for several days and nights; should the heat be too great, the bricks will be vitrified, and if not sufficient, they will turn out soft and friable.

It may seem strange, but it is none the less true, that wind can pass through a brick wall. This may have its advantages if we consider how rarely any provision is made for ventilation in the houses of the poor; but, as porosity is the cause, and as water can penetrate where air can, the necessity for constructing as far as possible impervious walls becomes apparent.

The quality of stone for building purposes varies, and hardness and compactness, or non-porosity, are the important requisites. Granite, of course, is well adapted for the purpose, but it is not met with in all neighbourhoods, and the labour involved in dressing it adds greatly to the cost of the building. The atmosphere of large towns has a perishing effect on some stones (those, for example, containing lime and magnesia), owing to the solvent action of rain and moisture when charged with gases which act chemically on stone.

Builders often use stone of the most inferior nature for window-sills, and for decorative purposes; it imparts an air of grandeur to buildings, but, owing to its perishable nature, the effect is but temporary. It is important that the builder should lay the stone as it was in its natural bed, otherwise it is more likely to perish.

Mortar is composed of sand and slaked lime, in the proportion usually of three of the former to one of the latter. The sand should be clean, sharp, tolerably fine, and free from small stones. Builders are apt to be very careless with regard to the freedom from dirt in the sand they use. Should it contain clay, marl, or earthy matter the mortar will not "set," but crumble to pieces; for this reason, it is advisable to wash all sand used for the purpose that is likely to contain any foreign matter.

The quantity of mortar used should not exceed what is necessary for insuring adhesion and uniformity of pressure. Walls built with inferior mortar, especially if a large quantity is used, are extremely friable structures, and they are far more porous than those put together with proper material.

Mortar ought to be prepared in small quantities as it is wanted, the sand being added immediately after the lime has been slaked. If it is allowed to stand it absorbs carbonic acid from the atmosphere, and when again disturbed for the purpose of being used it will have lost much of its adhesive quality.

Portland cement is the material best suited for building work in which strength is necessary.

Plaster which is applied to the interior of walls, and is used in the construction of ceilings, is prepared in a variety of ways, lime or cement being the chief ingredient. Durability, smoothness of surface, and absence of porosity, are the features of a good plaster. Unless it is smooth it is difficult to clean, and if porous it absorbs organic impurities from the atmosphere of the room, and in time becomes saturated with such impurity. Very inferior plaster is often used by speculative builders, consisting of a mixture of lime and sifted vegetable mould; such a plaster is exceedingly liable to break, for example, when articles of furniture are pushed against the wall. If the walls are papered a certain amount of support is afforded to the plaster, but in re-papering, when an attempt is made to remove the old paper the surface is certain to be more or less injured. It may here be remarked that the common practice of re-papering walls on the top of old and filthy papers is most objectionable, and ought never to be followed.

Plaster ought to be applied in three layers. The first, con sisting of equal parts of lime and sand mixed with ox-hairs, is applied on the face of the wall or on laths. The second, or floating coat, is composed of slaked lime and a little hair, mixed to the consistency of thick cream. The final coat consists of a thinner mixture of lime and water, sometimes with the addition of a little plaster of Paris to facilitate setting.

Keen's cement, Martin's cement, and Parian cement are all mixtures of calcined gypsum and other substances; they all set hard, and are capable of receiving a high polish.

Concrete is a mixture of lime or cement and gravel from which the fine sand has been separated. Stone crushed into sharp fragments, broken pottery, and slag answer the purpose, however, better than gravel, which, owing to the smoothness of its particles, has less adhesive properties. Concrete is used for foundations, for floors, or even for the walls themselves. ought to be made with cement when strength is of importance.

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Slate is an altered form of fine clay which has been compressed and hardened by natural processes. Its laminated formation allows of its being easily split into thin sections; hence it is frequently used for roof covering.

Tiles are formed of baked clay, and are either flat (plain tiles), or bent (pan tiles). The latter are twice bent—that is, in cross sections they present both a convex and a concave surface, to allow of their overlapping laterally.

Lead is the most suitable material for covering flat roofs and gutters, because it is very durable and can easily be worked.

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