CHAPTER VIII
Installing of French or Sub-soil Drains
When a building is erected on a site that is wet or springy, some means of carrying off the surplus water in the ground must be provided for, or the basement of the building will be flooded with water. For the thorough understanding of the methods employed in laying a drain of this kind, I will go over it carefully and the beginner can read it and then study it, and understand just how it is done. A site may appear to be dry on the surface of the ground and yet be very wet under the surface. If no information can be had regarding the site, it is always well to drain the site if it is on a slope or near a body of water and on the water shed of a river or lake. If a building is a large one and the foundation goes down very deep, the site should always be drained. The drain is laid under the basement floor and around the outside of the foundation wall on a level with or lower than the basement floor. The value of draining a building site when the building is first started is very often overlooked. The cost of the drain will be saved in a few years as the basement will be free from all excessive dampness. The expense of installing a sub-soil after the building is up and in use is great as well as inconvenient. The drain is called "sub-soil drain" on account of its location under the ground and on account of its duty of taking off all surplus water that is underground. With the surface water taken off by the surface drains and the sub-soil drained by the sub-soil drains, a wet building site can be made practically dry (see [Fig. 45]).
Materials Used in Sub-soil Construction.—The object of the drain is to collect water and carry it away from the building by means of pipes. Terra-cotta pipes, with or without hubs, are used. Perforated tile pipe is sometimes used. This pipe is unglazed terra-cotta pipe with 1-inch holes in the sides about 3 or 4 inches from the center. These holes allow the surplus water to enter the bore of the pipe and thus be carried off beyond the building site.
When the sub-soil of a small building needs draining, the trenches made for the house drain and its branches are used as a drain in the following manner: The trenches are dug deeper than is required for the house drain. The trenches are then filled to the correct level with broken stones. There is space between these stones for the water to find passage to a point away from the building. When this method is employed, some provision must be made to prevent the house drain from settling. When locating the drain, we must consider approximately the amount of water that is likely to be in the soil and required to be carried off. If there is considerable water, the pipes should extend all around the outside of the building foundation wall, also a main pipe running under the cellar bottom with six branches, three branches on each side.
If there is not a great deal of surplus water in the soil, the drain around the outside of the foundation wall should be put in and one drain line running through the basement will be sufficient.