Rural Hygiene. Henry N. Ogden
and well-drained soil around and below the cellar walls.
CHAPTER III
CONSTRUCTION OF HOUSES AND BARNS WITH REFERENCE TO HEALTHFULNESS
Any liability to disease that may come from faulty construction of habitations is likely to spring from a polluted subsoil. Such pollution vitiates the air drawn from that soil and is a source of danger on account of the resulting impurity of the whole atmosphere within the house.
Shutting out soil air.
We have already seen (Chapter II) how it is possible for soil charged with organic matter to deliver, either through suction from a heated house or on account of a rising ground water, soil air into the cellar, and also that moist air may enter the house in the same way. In order to prevent this, it is plainly necessary to interpose some air-tight or water-tight layer between the house and the soil, and also, since perfection in this layer is impossible, to make provision for draining away any water which may accumulate against the walls. Ordinary builders do not lay much emphasis on the importance of either of these precautions, and while one may often see cellar walls roughly and carelessly coated on the outside, with tar or asphalt, a thoroughly water-tight coating is not a common practice. Similarly, while draintile are often laid around a house, they are either laid so near the surface as to be useless or else they have no porous filling.
To prevent moisture from entering the cellar, the first provision should be a tile drain (not less than four inches in diameter) laid completely around the house (see Fig. 5) on a grade of not less than six inches in one hundred feet. This drain at its highest point ought to be one foot below the bottom of the concrete floor of the cellar, and more than this, of course, at the lower end. This should be laid before or at the time the foundations for the house are being built, although it is possible to dig the necessary trenches and lay the tile after the house is built. If the available grade is small, this drain may be laid in two lines directly under the cellar floor as shown in Fig. 6. At the points A the bottom of the tile should be at least a foot below the dirt on which the cellar floor will be laid, and at the point B, about two feet. This drainpipe is best laid with regular sewer pipe and without cement in the joints. Then coarse gravel should be filled in around this tile so as to allow water to enter the pipe without carrying soil that later might settle in the pipe.
Position of outfall.
There is always a question of where this drain shall end and into what it shall discharge, for in some soils this drainpipe may discharge continually. To allow the drain to empty on the ground means that its outer end will be broken; that if discharge takes place just before freezing weather, the drain will fill with ice and be broken, so that some other method must be devised. If the outer end can be laid into a brook where the velocity prevents the water from freezing, or where the outer end can be kept below water, a satisfactory disposal is found. Otherwise, it is better to discharge into a small covered cesspool, provided the soil is sufficiently porous to take care of the water, and provided the level of the ground water allows the construction of such a cesspool. In any case, it should be at some distance from the house, so that if it overflows, the water will not seep back to the cellar walls. By water-proofing the main wall and then backfilling against the wall with coarse gravel or broken stone, the same results as with open areaways are obtained and at a much smaller cost.
Dampness of masonry walls.
One fact peculiar to all kinds of masonry and known to all careful observers is that stone work, brick work, and concrete will allow dampness to permeate, whether it comes from water-bearing soil or a driving rain. One objection to concrete-block houses has been that a hard rain would cause moisture to form on the inside. Brick buildings have the same defect when the walls are built solid.
An air-space in the cellar walls is the only way of insuring a dry cellar, if the bottom of the cellar is below the level of the ground water. A four-inch course of hollow brick may be used on the inside, or the wall may be actually divided into two walls with a space between.
Figure 7 (after Warth) shows three different ways by which an air-space is secured and the two component parts of the wall held together. In the top view, the two walls, one eight-inch and one four-inch, are held together by wire ties, leaving an air-space of about four inches. In the middle drawing the walls are tied together by making the air-space three inches wide and then lapping the brick laid as headers over both walls. In the bottom view special terra-cotta blocks are used which pass through both walls. There can be no question of the value of such construction in eliminating dampness from the inside wall, but, it must be admitted, the cost of the walls is increased somewhat.
Use of tar or asphalt on the wall.
Instead of an open space, nowadays, it is more customary to thoroughly plaster the outside of the cellar wall, and then paint it with a tar paint put on hot, which will adhere fairly well to the cement or masonry. Asphalt cannot be very readily used for this purpose unless it is an asphalt oil with but little bitumen paste. A paving asphalt, for example, even applied hot, does not adhere to the masonry, but slides down the walls as fast as it is applied. A successful method, however, of using such asphalt is to build the cellar wall in two parts, separated about half an inch, and filling in the intervening space with liquid asphalt. In this way, the asphalt is held in position, and is an absolute prevention of dampness.
Another method used successfully in the construction of one of the large railroad stations in Boston consists in painting the outside of the wall with tar and then pressing into the hot tar several layers of tar paper, the separate sheets overlapping in a special coating of tar. These sheets are thus made continuous around the building and under the basement so that no water can enter the building.
A cross-section of one of the depressed tracks entering the Boston Station is shown in Fig. 8. The heavy black line represents ten thicknesses of tar paper, each one thoroughly painted with a thick paint of hot tar. It should be noticed that this water-tight coating is inclosed between masonry walls, so that the coating cannot be injured.
It is possible theoretically by these methods to build an underground cellar so truly water-tight that it could be set down in a lake, where it might float like a boat and not leak a drop, and there may be some locations that require such construction, such as a low river valley or an old salt marsh or a city flat, where no adequate drainage is provided. But practically such construction will always be found expensive, and is, in most cases, unnecessary and ineffective, as already indicated, and where the percolating water cannot be tolerated, involves the installation of some kind of pump to throw out the water that will inevitably, in larger or small quantities, pass through the best water-proofing. It is, therefore, the part of wisdom to place reliance on draining the water away from the house rather than on water-proofing the cellar wall.
Dry masonry for cellar walls.
It may not be out of place to add a word of caution against the practice of building cellar walls of loose stone, without mortar. They