This section is from the book "Modern Buildings, Their Planning, Construction And Equipment Vol1", by G. A. T. Middleton. Also available from Amazon: Modern Buildings.
When a cross wall has no openings in it its thickness has to be ascertained indirectly, as shown in Fig. 26, where the sum of 2 ft. 4 in. and 3 ft. 2 in. is 5 ft. 6 in., and the difference of 10 1/2 in. between this and 6 ft. 4 1/2 in. is obviously the thickness of the wall in question.
It was by the adoption of these methods only that the somewhat irregular little cottage was measured whose ground plan is shown as an example in Fig. 28 opposite, and almost anything can be done in the same way, by gradual extension of the process; though occasionally an irregular outline may have to be obtained by stretching the tape across an opening and taking ordinates to it as shown in Fig. 27, - or a chalk line drawn on the floor or ceiling may have to serve in place of the tape.
When a building consists of several storeys it is, as a rule, only necessary to measure the plan of the ground floor in its entirety. This can be plotted carefully on drawing paper, testing everything with the diagonals and remeasuring if any discrepancy appears. The drawing thus made may be treated as the basis upon which to found the measurements of other floors, all main walls, which obviously run through on to other floors, being traced as many times as there are storeys, including basements, - or if there are several storeys, one tracing may be made and several sun prints, with black or brown lines on white paper, made from it. These tracings (or sun prints) may be pinned on to small drawing boards and used for detailing the other floors on, the outline being now known to be correct, and any alterations in the thickness of the walls being figured before detailed measurements for the positions of door and window openings, partitions, stairs, etc., are taken. Of course, if windows occur exactly above one another on every floor, they also may be shown on the tracings, it being easy to figure any small alterations either in size or position. Stairs should be shown and measured separately on each floor, and ought to be numbered as well as measured, and the number in each flight recorded.
Fig. 28. Survey plan of a Farm Cottage.
Sections are measured in the same manner as plans, except that diagonals are rarely needed - only if the walls, when tested by a plumb-line, prove to be out of vertical, or if the floors are not level. The most common difficulties occur in ascertaining the thicknesses of floors (often to be measured at staircase well-holes) and the slopes of roofs. Fig. 29 illustrates the sketch section of the cottage whose ground plan is given in Fig. 28, and shows, better than any amount of description could do, how all that is necessary has been obtained with very few dimensions. As a rule sections are best measured through a staircase, and the number of stairs should be correctly shown and figured both on section and plan.
Elevations are similarly measured, the work being simplified by the positions of the main openings having already been located on the plans; but architectural features have necessarily to be recorded in general outline and detail. The positions of continuous horizontal lines are usually ascertained first, and heights are measured from these, either upwards with the 5-foot rod or downwards by means of a tape having a weight suspended from its ring. Several points in a curve, for example, such as O, P, and Q (see Fig. 30), can in this way be very exactly determined by means of horizontal measurements x, y, and z, and corresponding vertical measure-ments a, b, and c, downwards from a horizontal string course or moulding.
Fig- 31 shows a win-dowin simple plate tracing with all essential dimensions figured and the rest sketched, the purpose for which it was needed not having demanded an absolutely correct drawing.
Mouldings are almost always measured on a system of ordinates, the contours being sketched, 'their outlines being ascertained more accurately by the sense of touch than in any other way if an actual section is not visible, the fingers being passed gently into the hollows and along the contour. It is in this way that the actual contours shown both in Fig. 32 (which is a section of the arch moulding of the door to the Hotel du Due de Rouen at St. Brieuc) and in Plate III. were obtained. The measurements for Fig. 32 were taken as shown, but Plate III. was drawn to scale on the spot, the measurements being taken as co-ordinates along the dotted lines. In order to show clearly how the vaulting ribs sprang by inter-penetration from the pier in this very interesting and characteristic piece of French "Flamboyant " work of the sixteenth century, it has been necessary to employ colour, the principal arch and pier below being shown in sepia, the transverse ribs of the vaulting in blue, and the d ia-gonal ribs in yellow.
The more ornamental details of a building are frequently sketched to a larger scale, either in front and side elevation or in perspective as shown in Fig. 33, their positions being described or indicated by reference letters; but whenever time permits it is much better to make elaborate elevational drawings to scale on the spot at once, as was done with the half bay of the Cloister of St. Maclou at Rouen, shown in Fig. 33A. There the intricate detail could scarcely have been accurately placed had each little bit been sketched separately; and it is doubtful whether in the end any time would have been saved, as the drawing was commenced and completed in the course of an afternoon. No set-square was used, but all lines were drawn with the aid of a small T-square working along the edge of a drawing block. The same procedure is followed in such a case as when rough sketches only are made on the spot, general covering dimensions being taken first and the detail filled in afterwards gradually, starting with the major and finishing with the minor features, correctness being checked both by scale and by totalling the smaller dimensions to ascertain whether the total coincides with the covering measurement.
Measured drawings of this sort are not only essential preludes to the preparation of schemes for alterations, but their preparation has also an exceedingly high educational value if the examples be well chosen.
Finally, at the risk of repetition, it must be urged that it is far better to take too many dimensions than too few, that it is unsafe to make assumptions, and that every important point should be located by at least three dimensions concurring at that point.
Fig. 33A. Plate iv.