CAR
98
CAR
“ The next order is joists, of which there are five kinds,viz., common-joists, binding-joists, trimming-joists, bridging-joists, and ceiling-joists. First, common-joists are used inordinary buildings, whose scantlings in fir are generally madeas follows, viz.:
Common joists, as used insmall buildings.
Length
Scantling in
in feet.
inches.
6
by 2£
9
by 2A
12
8
by 2j
In this table, it may be observed, the increase is not veryregular: why should the scantling of the joist 9 feet inlength, be no more than that of 6 feet? This must be amistake.
“ But in large buildings, the scantlings are much larger,where it is common to make joists of the following dimensions:
Common joists, as employedin large buildings.
Lengthin feet.
Scantling ininches.
6
5
by 3
9
U
by 3
12
10
by 3
“ As oak is much heavier than fir, it is customary to makethe scantlings of oak-joists larger than those of fir ; butI believe it to be entirely wrong, for the reason before given,relating to the strength of timber.
“ Secondly, binding-joists are generally made half as thickagain as common-joists of the same lengths;” and “ are framedflush with the under surface of the girders, to receive theceiling-joists, and about 3 or 4 inches below their upper sur-faces, to receive the bridging-joists ; so that the upper surfacesof the bridging-joists may be exactly flush or level with thegirder to receive the boarding.
“ The distances that binding-joists should be laid at, shouldnot exceed 6 feet, though some lay them at greater distances,which is not so well, because the bridging and ceiling-joistsmust be made of larger scantlings to carry the weight of theceiling and boarding, and consequently a greater quantity oftimber must be employed. But, however, as this particularis at the will of the carpenter, I shall only add, that thescantlings for bridgings of fir, to tlieir several lengths, areas follow:
Bridgings of fir.
Bearing.
Scantling.
feet
inches by inches
6
4 by 3
8
5 by 3
10
7 by 3
“ Their distances from each other, about 12 or 14 inches.”He then proceeds with roofs, as follows:
“ As the common method of framing the trusses of prin-cipal rafters of large roofs, is to lay the whole weight of thebeam and covering upon the feet, they therefore should be
secured at the beam with iron straps, to prevent their fly in S i |out, in case that the tenons should fail; but as I apprehend jthis method was capable of improvement, I therefore con- ,sidered, that if under the lower parts of principal rafter 9 * Ithere be discharging struts framed into the beams and pricked | >posts, they will discharge the principal rafters from the ;greatest part of the whole weight.” ! '
This is certainly an improvement, but not of his, as it is 1® , ibe found in Price’s Carpentry, among his designs of roots r ,it gives an additional security to the principal rafters, so that | jif the outer abutment should fail, the roof will still be sup' i 1ported by the inner one. g i j
He gives the scantlings of fir-timbers in a roof,.as follows - ■
Beams.
Length
Scantling.
feet
inches by inches.
30
6 by 7
45
9 by 7
60
10 by Si
75
10J by 10
90
12 by 10J
Principal Rafters.
Length
Scantling
at Top.
Scantlin
g at Bottom.
feet
inches
by
inches.
inches
by inches.
24
5
by
6
7
by
6
36
7
by
6
9
by
7
41
9
by
7
10
by
n
60
10
by
n
10
by
9
72
10
by
9
11
by
9J
Small Rafters.
Length
Scantling.
feet
inches by inches.
8
4£ by 3
10
5 by 3
12
6 by 3
Besides the formation qf the end of a purlin, attemptby Price, Langley also notices the bevels of the jack-rat teWe now come to the description of his diagrams. f9
“ The Figures 1 and 2, Plate 9, are examples ofmade of short lengths, which I have given for the diversof the curious.”
These floors are of a similar construction with those sb .in the works of Dr. Wallis. Godfrey Richards, ourauthor, has also inserted two kinds of floors of this natone constructed of hexagons and triangles, the other cons ^ing of squares laid diagonally in respect of the plan, wt ^hexagon in the middle. These examples were executethe old Somerset House, and were at that time a novel yEngland. This species of naked-flooring may be seen eworks of Serlio. It had its origin in Italy , and was th jtransported to this country. Though from the pri ncl P le t j 1 ;gconstruction, the timbers mutually support each ot ^ er ’. ( .j,erspecies of joisting has not been found advantageous, elin saving of expense, or with respect to strength, bu ^contrary; it has therefore in modern works beencontinued.