Subsoil-drainage will seldom be found under or around old houses, or, if drains were originally laid, they were probably of stone, and have either collapsed or been choked with silt. In damp situations, houses will often be made drier by laying deep subsoil-drains around the house, without disturbing the fabric itself. These drains must, as explained in Section II., Vol. I., pp. 69 71, be disconnected from the sewage-drains. Where necessary, branch subsoil-drains must be carried under the house to the specially damp places.

Damp basement-floors, whether of flags or tiles, may be covered at once, if the height of the room will allow, with a thin coat of cement (for the purpose of levelling the floors), on which one or two coats of natural or artificial asphalt may be spread, and the surfaces can then be formed with grit rolled into the asphalt, or with tiles, flags, or wood-blocks, or with a layer of fine concrete about l 1/2 inches thick. Where the height of the room must not be reduced, the old floor must be taken up, the ground excavated to a depth of at least 6 inches, and an impervious ground-layer and floor formed, consisting of a 4 1/2-inch bed of compact concrete floated to a smooth surface and covered with an asphalt layer, which may be finished with a concrete or other surface as described above, after the manner of the floor shown in Fig. 27, p. 81, vol. i.

Sometimes basement-floors in damp ground are formed with flags, artificial or natural, with the edges ting on low sleeper walls, as shown in Fig. G78, or with the corners carried on small piers of stone, brick, or concrete. The latter arrangement is suitable for artificial flags, all of the same dimensions, but the other is the more econoini-eal for natural flags.This method has little to recommend it save economy; the spaces under the flags, while undoubtedly tending to the dryness of the floor, do not prevent the ground-air entering the building, and furnish a convenient harbour for cockroaches and other vermin.

The dampness of basement-walls will probably be considerably reduced by drainage of the subsoil, but one of the greatest improvements will be the formation of an open area around the building, as shown in Fig. 18, p. 56, vol. i., or of a dry area (although this is less satisfactory), as shown in figs. 23 and 24, p. 79, vol. i. If an open area is formed in connection with a stone building, the outside of the-walls will probably prove to be very rough. and must be either roughly brought to an uniform surface and then covered with cement stucco, or faced with new stone which can be finished at the top with a chamfered base, as shown in Fig. 679; or the whole of the outer thickness of stone can be rut out, and this part of the wall underpinned with stonework in cement mortar, but this method will prove very expensive. A perforated damp-course, as shown at a, will assist in keeping the wall and floor dry.

Where the formation of an open area would prove too costly, and when it is impossible to drain the subsoil sufficiently deep, on account of the relative depths of the basement and of the available outlet, some other method of obtaining dry walls within the basement must be adopted. One method consists in building a 4 1/2-inch brick wall on the new ground-layer or floor, leaving a cavity, not less than

Fig. 67.   Flagged Basement floor with Air space beneath

Fig. 67. - Flagged Basement-floor with Air-space beneath.

Fig. 679.   Old stone Wall faced with New Stone after forming open Area. A, new damp course.

Fig. 679. - Old stone Wall faced with New Stone after forming open Area. A, new damp-course.

2 inches wide, between it and the old wall; this cavitv must be closed at the top, and ventilated by means of grated openings into the basement at or near the floor-level, and into the open air above the ground, as shown in Fig. 680. If the rooms in the basement will be reduced too much in size by the arrangement just shown, the new brickwork may be built on edge, and will then be only 3 inches thick instead of i\ inches.

Still greater saving of space will be effected by forming the cavity only 1/2 or 3/4 inch wideand running it full of artificial asphalt every three courses; the basement-rooms in this case would only be reduced 5 inches at each external wall, or, if the bricks are built on edge, only about 3 1/2 inches. See pages 77-78, and 80-82. Section II. Vol. I., for further information as to asphalts and their application. It will be gathered from reference to these pages that an excellent arrangement would be the covering of the exterior of the wall with an asphalt layer; but this would entail a great expense in excavation, preparing the wall, Ac,, but the cost of the brick lining would be saved.

Plates of asphalt are now made by the Lim-mer Asphalt Paving Co. for affixing to damp walls, but these can only be used where appearance is not of much importance.

A more ingenious arrangement, and one more generally applicable to the damp walls of basements, has been devised by Mr. William White, and consists in the use of unglazed tiles with an asphalt lining between them and the wall. As shown in Fig. 681, the tiles are roughened on both sides to secure the thorough adhesion of the asphaltic composition on the one side and the plaster or cement on the other. Before laving the tiles, the plaster must be removed from the face of the wall, and the joints well raked out to afford a key for the composition; a row of tiles is then placed in position about half an inch from the wall, and held there by means of a simple wood framework. Into the cavity thus formed. the molten composition is poured, and in a few minutes sets sufficiently to allow the framework to be raised and another row of tiles placed in position. A coat of plaster or cement applied to the exposed face of the tiles completes the work. The total thickness of this damp-proof lining, including composition, tiles, and plaster, need not exceed an inch or thereabouts. The asphalt lining may be connected with the asphalt floor-layer, and a continuous damp-proof covering be thus obtained.

Fig. 680.   Section showing Inner Wall and Ventilated Cavity for improving Damp Basements. A, new brickwork forming cavity; B and c. air grates.

Fig. 680. - Section showing Inner Wall and Ventilated Cavity for improving Damp Basements. A, new brickwork forming cavity; B and c. air grates.

Fig. 681.   Full size Section of White's Tiles, with Aspbalted Cavity for Damp Walls, A. mortar joint with part raked out. B. asphaltic composition; C title; D, plaster.

Fig. 681. - Full-size Section of White's Tiles, with Aspbalted Cavity for Damp Walls, A. mortar joint with part raked out. B. asphaltic composition; C title; D, plaster.