CHAPTER X THE BuILpING—ItTs DRAINAGE (Part 1)

CHAPTER X THE BuILpING—ItTs DRAINAGE (continued) Layout of Drainage Schemes. Having fully considered the principles underlying the design of a drainage scheme, we may next deal with their application. An accurate block plan of the building must be prepared, and the position of all soil, waste and rainwater pipes carefully marked on it, together with the position of any W.C. which is to be con? nected directly to the drain, such as a servants’ closet on a ground floor, with no other closet over it. The arrangement of the drainage will, of course, depend on the character of the building, the nature of the site and the local by-laws. The local authority may require rain and surface water to be kept separate from waste water and “soil” or may permit all to be delivered into a “combined” sewer. They may require an intercepting trap and F.A.I. or the by-laws may forbid them or make them permissible. Again, with a terrace house, the main drain must necessarily pass under the building if the sewer is in the road in front, whereas in the case of a semi-detached or detached house the drains can usually be kept quite outside the site of the building. Drainage Schemes for Terrace Houses. A few example plans may be given. Figs. 349 and 350 show block plans of two small terrace houses of different plan. The various inlets to the drain are lettered with distinctive letters and a reference table given to show their meaning. The same lettering will be adopted in further examples. The heads of the gullies under the rainwater pipes are not shown owing to the smallness of the scale. In both the examples under notice it is assumed that the local by-laws require an intercepting trap and F.A.I., and the inter- cepting chamber is placed in the front garden and the fresh-air inlet carried up behind the pier which carries the front railings. Channel gullies are shown taking the bath and sink wastes. In Fig. 349 the drainage from a yard gully at the back is turned into the drain from the servants’ W.C., in order to assist in flushing it. The vent pipe is shown connected to the manhole at the back, but if the manhole had a closed channel it would have to be joined to 326 THE BUILDING—ITS DRAINAGE STAN TSITTIESS S Vy : SY “, os S77 My, 327 THE BUILDING—ITS DRAINAGE ‘YHId=d 'FIONNVW=HW ‘'FLSYM HLYG=M'G “ATIGNVHO ON/LAFO -YUM/="DT AVAL INILAFIAFLN/ =LT XFTIND GAVA="9A ‘LIINI BlY HSFAF =7'VY XAITIND TAINNVHD='9'9 ‘Fdid ILSYM ANIS=M'S ‘FIdid LNIA=A '‘Idid LNIA ONY WOS=NB'S AITIND GIdSVAL ANY Fdid YILVMNIVY = MA pets : LYNOITAOZ TSNOH FIVAAIL EELEPEL Q © <2 = Pn, 8 « Q Uy Y > S = w G ps a yR w 9 wD =a qQ = x wy 9 as w as = x « Q = yt Q © KR © S Q Pty & N g ty x S ery x Y = ~ 4 Nj x ~Q ~ 3 9 “ —_ 328 THE BUILDING—ITS DRAINAGE the drain. It would appear to have been better to put the vent pipe in the angle between the servants’ W.C. and the main building, but it is shown otherwise owing to the existence of a skylight near that point. In Fig. 350 the drain from the servants’ W.C. is carried, in cast-iron pipes, under the back addition, for two reasons: (1) that the owner does not desire any manholes on the small grass plot at the back; and (2) that to proceed otherwise would mean two additional manholes, making four in all—rather a prohibitive item in the case of a small terrace house. In most cases, the soil-pipe would be regarded as a sufficient vent pipe for the system, but an additional one might be added where shown, adjoining the entrance of the sink waste. Drainage Schemes for Semi-detached Houses. In Fig. 351 a pair of semi-detached houses are shown drained together, as is often done in the London district. It will be seen that a common passage leads to the tradesmen’s entrances at the back of the houses and that the main drain is laid under this. Its course is not quite straight from end to end, as to make it so would bring the back manhole under the fence. Inspection bends are placed on two of the rainwater drains in each case. By placing the back manhole farther from the street, the rainwater drain at the back of each house might have been given one change of direction in- stead of two, but in this case the foul drains would have had to enter the manhole with a very sharp curve and the lesser evil has been chosen. It has been considered better, also, to connect the vent pipe to the drain from the W.C., a foul drain, rather than to the longer drain taking rainwater only. Detached Houses. <A detached corner house is shown in Fig. 352, separated from an adjoining house by a narrow passage. The peculiar placing of the sanitary fittings makes this case a difficult one to deal with economically, owing to the narrowness of the passage. The bath waste and soil-pipe might have communicated with the same manhole by placing the latter nearer the street, but the small space available between the manhole and the building would have caused very awkward junctions and the method shown is considered the better for this reason. It will be seen that the ground-floor W.C, is not under that on the floor above, and the drain from the former is therefore taken direct to the intercepting chamber. An additional manhole might have been put at the | back to take the two sink wastes and the rainwater, but the increase — in cost, over that of the arrangement shown, would not be justifi- able. An inspection junction, I.J., is used at the connection of 329 ITS DRAINAGE THE BUILDING ISNOH GFHIVLIG-IWIS EXAMPLE OF JOINT DRAINAGE FOR SEMI-DETACHED HOUSES, (LOCAL BY-LAWS REQUIRE INTERCEPTING TRAP AND F.A.1.) 330 THE BUILDING—ITS DRAINAGE the second sink waste. It will be seen that a good position is obtainable, in this example, for the vent pipe, right at the head of the system. Use of Air-disconnected Drains. A modification of the arrange- ment shown would be to make the long rainwater drain from the right-hand side of the house an air-disconnected drain (see Chapter VIII) by putting in, close to the intercepting chamber, a trapped yard gully with side inlet for the drain and using untrapped gullies at the feet of the rainwater pipes. Separate Drains for Surface Water and Foul Waste. Fig. 353 shows a much more extensive system than those already given, and illustrates the drainage of a fairly large bungalow on the separate system, with its own system of sewage disposal, the latter installation being situate some three or four hundred yards from the house, With the exception of those marked 6 inches, the drains would be of 4-inch pipes. As the septic tank system is used, grease traps are provided instead of channel gullies, the former being of the lifting tray type, as a flushing grease gully would not be permissible owing to the necessity of keeping grease out of the septic tank. At one point, to the south of the building, an ordinary flushing gully is provided, taking the outlets from two ordinary grease traps, and flushed by an automatic flushing cistern placed high up in the scullery, The intercepting chamber, being some considerable distance from the house, is covered by an iron grating to act as a fresh-air inlet. It will be seen that a vent pipe is provided to the head of each of the principal branch drains. Working Sections of Drainage Schemes. Having prepared the plan of the drainage scheme, the next thing is the preparation of the working sections. The levels along the lines of the proposed drains must be carefully taken and the sections plotted, showing the existing surface of the ground. The method of taking the levels and plotting the sections is beyond the scope of the present work, but Figs. 854-856 give examples of completed sections after the lines of the proposed drains, positions of manholes, etc., have been added. They refer to the drainage of the bungalow shown in Fig. 358, Fig. 354 giving the section from the soil pipe in the N.W. corner, past manholes Nos, 1, 2 and 3, on to No, 4. Fig. 855 gives a section of the line running from N. to S., from the R.W. pipe to manhole No. 8, and Fig. 856 that from the vent pipe on the N. eastward and southward past manholes Nos. 6 and 7 to No. 4. These three sections form only part of the set which would have — to be prepared for this case, but they serve as examples, and there is no advantage in repetition. The levels should be taken in THE BUILDING—ITS DRAINAGE 331 FOOTPATH SIDE ROAD w Y 3 Ss = Q wy = 9 h | KR uy Q MAIN ROAD 352 EXAMPLE OF DRAINAGE FOR DETACHED HOUSE, (IF LOCAL BY-LAWS FORBID INTERCEPTING TRAP AND FA.I, THEY WILL BE OM/TTED.) 832 THE BUILDING ITS DRAINAGE reference to some clearly defined bench-mark, the position and level of which should be shown on the sheet of sections. Use of Ramps. It will be seen that against each ordinate on the sections two heights are figured, the greater reading being of course the existing surface level, and the less the level of the invert of the proposed drain at that point. (Note. The “invert” of a drain is the lowest point of its interior.) The upper end of the drain should be shown about 2 feet below the surface, and the line of drain drawn in such a position as will give a reasonable gradient, without coming nearer to the surface than about 2 feet. The fall shown in the case of Fig. 356 is perhaps excessive, and it might be better to adopt the section shown in Fig. 357, which introduces what is termed a ramp or drop pipe, in order to give a more reasonable gradient. The ramp is shown adjacent to the manhole at R, the drain being continued into the manhole to provide means of inspection and cleansing. The ramp is preferably encased in concrete. The detail of such a ramp or drop pipe is shown in Fig. 358. A stopper is sometimes placed at SS (the rodding eye), but better drain ventilation is obtained without it. If the ramp is not more than about 18 inches in depth, it can be formed in the chan- nelled floor of the manhole. Arrangements of this sort are sometimes described as “tumbling bays” or “drop manholes”, and they may be used, with small modifications, to connect a branch drain at a higher level to a main drain or private sewer at a lower level. The B.S. Code of Practice on Building Drainage shows a preference for a vertical drop pipe to connect the two levels instead of the sloping ramp, and in this case it is wise to carry the drop pipe up to the surface and provide a hinged access cover in case the lower section should get blocked. Position of Sanitary Fittings. Before leaving this question of plans and sections, it may be pointed out that before the ground plan of any building is inked in by the draughtsman, the position of all the sanitary fittings, their waste pipes and the drains to which they are connected should be finally determined. This can only be done successfully by a careful study of the proposed elevation, so as to select such a position for the soil, waste and vent pipes as will allow them to be carried down without unnecessary bends. This point may appear of minor importance compared with the tout ensemble of the elevation, but whatever effect the elevation may have on the beholder, it can have none upon the health of the occupants of the house, and a badly arranged waste pipe may. 333 THE BUILDING—ITS DRAINAGE (‘Gv0e N/ SYIMIS YILVM FOVIANS GNV TNO FLVYVAIS OLN! 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Having prepared the plan and sections, we may proceed with the setting out. The lines of the main drain and branches should be first of all pegged out on the ground before any excavation is commenced. The next point is the setting out of the gradients. Sight Rails and Boning Rods. The only accurate method of securing a perfectly regular gradient is by the sight-rail and boning- rod system. On either side of the proposed drain, at the upper and lower end of each length of drain, a drain pipe of good diameter, say 9 inches, is set up as shown at D.P. in Fig. 359. In each of these an upright post is planted, being well packed round with earth orsand. Sight rails, S.R., are then fixed to the posts at each end of the length of drain, at such a height that their upper edges will set out in the air an imaginary line parallel to the intended drain, and at a convenient height above ground for a man to sight. Sight rails are always fixed first at the point at which the drain’ commences, which will be the lower end, since it is the outfall level which is usually more or less rigidly fixed by circumstances, such as the level of an existing sewer, and because drains are invariably laid uphill; next, at all changes of direction or gradient, at any convenient intermediate point when desired, and finally at the top end of the drain. The posts should be well away from the edge of the trench to prevent disturbance by falling earth. The sight rail is an ordinary wooden straight-edge, fixed level from one post to the other. The Boning Rod or Traveller. Fig. 360 shows the elevation and a side view of an adjustable boning-rod, or traveller. It is really an elongated T-square, having the blade in two pieces, and capable of adjustment to any desired length by means of iron bands and clamping screws at $, 8, At the foot is an iron shoe, projecting so as to enable it to be rested on the invert of the pipe. Levelling Calculations. The method of fixing the sight rails at the correct height can be explained by the aid of Fig. 861. It is assumed here that a drain 160 feet long has to be set out at a gradi- ent of 1 in 60 from a length of drain, already laid, whose invert level is 24°75 feet above datum. At a gradient of 1 in 60 the rise in 160 feet will be 48° = 2-66 feet, so that the level of the invert at the upper end of this length of drain will have to be 24-75 + 2-66 = 27-41, as figured in the illustration. Two sight rails are shown in the section, and the level should be set up midway between them to eliminate any error of collimation in the instrument. ———— ee 336 THE BUILDING—ITS DRAINAGE The levels figured on the section (Fig. 361) show that the depth of the invert of the drain below ground at the lower end of this length is 31-20 — 24-75 = 6-45 feet, whilst at the upper end it is 32-41 — 27-41 = 5-00 feet. If then we put the sight rails 10-50 feet above the invert of the drain the height of the sight rails above the ground will be 10-50 — 6-45 = 4-05 feet at one end, and 10:50 — 5-00 = 5-50 feet at the other end. This will be a con- venient height for sighting in the manner which will be described later. It should be noted at this point that the ground level is of interest only for this purpose, of finding out what will be a con- venient height for the sight rails above the drain. Having selected this height the “ground” levels are disregarded in what follows, as such levels are likely to be changed slightly, by falling in of stones, or by earth thrown up, and are therefore quite unreliable as a basis from which to set out the levels of the drain. Use of Surveyor’s Level. In the present instance, having decided that the sight rails are to be 10-50 feet above the drain, they must be set up at reduced levels of 24-75 +