R O 0
3<)1
ROO
5H(| j t ®^ould be made for its expansion and contraction,Ttio^ .'^desirable to protect it from oxidation by painting.^Oibep ■ lr ? n ' s f ar stronger for its size than any kind of•oeibi.’ 11 is neither so strong nor so cheap as yellow-fir,J° r height.
Figure 1, is the roof of the chapel of the royalIt at Greenwich, constructed by Mr. S. Wyatt,hip instructed with two queen-posts, and is similar tof' 0t > tn, 0tl< * kind °f roof above described, but it has in addi-
1 tw 0
}>ea m
struts from the foot of the queen-posts to the strain-1 >eat] l w bicli abut against a second straining-piece under-*i>e 8 t r • . ^ rst j the tie-beam is also further suspended froml> 0 s e lnil1 g-beam by an iron-rod, which answers the pur-
f if een ' post '
Allowing are the scantlings of the various timbers:—
Inches
^4,'J'hft . Scantling,
t'e-beam, 57 feet long, the span of the
q w alls being 51 feet . 14 X 12
g“ een -P°sts.. 9 X 12
b, g, is. 9x7
S t ^! n l n g-beam . 10 x 7
Ki^'^-piece . 6x7
®> Camv Pal rafters . 10 X 7
^ . er -beam, for the platform . 9 X 7
^ Ir on rod, supporting tie-beam . 2 X 2
]„*’ r , US3es a re seven feet clear ; the platform is coveredinch ’ Wb * cb * s supported by horizontal beams six byPhe .*
frj fitaj n , lnt *oers of this truss are well disposed, and perhaps, ess w ood than most roofs of the same dimensions,i Spied*' 3 tbe rooP oP haul’s, Covent - Garden,11 ^9fi Hardwick, and constructed by Mr. Wapshot,
1 p his r
k Va r ig„°^ although of the same general construction as the
: Pl , om it in several particulars. The lower portion
truss, but in addi-18 a second pair of principals, which are supportedids, and the lower principals thus becomingthe queen-posts are continued up to the
w -- r ._ - r .—. r _, .. rr „„
?*)y aiwM^ r b 7 studs, and the lower principals thus becominS( c ipals ' ar ’ es > the queen-posts are continued up to tlih^inin- : and a king-post is carried from the apex to theth„ h heam.acantlir
tings are :—
k
I'he
Inches
a QuL tie ' beam , spanning 50 feet 2 inches
l Vai n n ‘ posts . -
* ^n^ ng ; beam .:. 10
Sttu, h ost > 14 inches at the joggle . 9
. 9
t’ b >I‘ri tl „- ar y rafters, at bottom. 10
Sta<j s 'Pal rafters, at bottom .10
supporting the principals. 8
V1 ! 8 roof i
<a ij> 0 j 18 much better constructed than the original one5)j a bi c p° nes ' A truss of the present design contains onlyof;’ and vv et 0p Umber, whereas that by Inigo Jones had
Scantling.
16
X 12
9
X
8
10
X
8
9
X
8
9
X
8
10
X
8i
10
X
8 i
8
X
8
% vv as
very insufficient at the joggles, and had somefor t rS Vei T m disposed : the interior truss is well con-
So ° r sun " • - r - -—-
t), e PP°rting the exterior, which reaches seven feet
loti’haiug '^aUs. The tie-beam has, perhaps, too much cam-: l tbe n i n S '? iuehes ; for since it acts as a string, it will! 3 g le settling of the roof.
j n e s sp re P res ents the roof of Drury-lane theatre, 80 feet; ‘ fl ' v ar!i n, ri ln< i ihe trusses 15 feet apart; constructed byay Saunders. This was destroyed by fire
5 £
This is rather a curious form of roof; the principal trussis simply one of the second class with queen-posts and strain-ing-beam, but above this, and partially resting upon it, arethree other smaller trusses, which form the outer-roof.These are simple trusses of the first class with king-post andstruts, the central one having a continuous bearing on thestraining-beam of the main truss, and the side ones restingat one end on the straining-beam, and at the other on
the wall.
Inches
Scantling.
b, b, Rafters. 7x7
C, King-posts . 12 X 7
D, Strut . 5x7
E, Purlins . 9X5
G, Pole-plates . 5X5
h, Common-rafters . 5x4
i, Tie-beam. 15 X 12
k, Posts to ditto . 15 X 12
l, Principal braces to ditto.14 and 12 X 12
M, Strut. 8 X 12
N, Straining-beam . 12 X 12
The principal beams are trussed in the middle space withoak braces, five inches square. This was requisite on accountof its width, which is 32 feet, that the floors might carry thework-shops necessary for the use of the theatre. This truss,which is most admirably constructed, is hardly to be equalledfor strength, stiffness, and lightness, and will safely bear aload of nearly 300 tons, which is four times more than everit is likely to be loaded with.
Plate VII. Figure 1, exibits the roof of Covent Gardentheatre. The tie-beam in this case is supported by five sus-penders, a king-post in the centre, and two queen-posts oneither side; between the two innermost queen-posts is astraining-beam, and on the other sides of them are auxiliary-rafters, which abut against a shoulder near their heads. Astrut is carried from the foot of the inner queen-post to thehead of the outer. The straining-beam is suspended by twoqueen-posts, between which is another straining-piece, and astrut from their head to the angle formed by the king-postand straining-beam below. The posts are all made double,and are shown in the Plate above the roof in their respectiveplaces. This roof was also destroyed by fire, March 5, 1856.
Figure 2 represents the present roof of Drury-lane theatre.There are here both principal and auxiliary rafters, the tie-beam being suspended at two points from the former, and attwo from the latter, the two first queen-posts being the innerones. These are kept apart by a straining-beam, againstwhich they are pressed from the other side by the auxiliaryrafters ; struts are placed between the feet of the principaland the head of the secondary queen-posts, and the bearingof the sub-rafters is still further reduced by a strut from thefoot, and on the other side of the smaller queen-posts. Thestraining-beam is supported by a king-post from the apex ofthe principals, which in their turn are supported by strutsfrom the foot of the king-post, the other portion having acontinuous bearing on the auxiliary rafters.
The Figure above on the left-hand, shows how the timbersjoin at the top of the queen-posts, and that on the right howthe timbers join at the end of the tie-beam.
The roof over the church of St. Martin-in-the-Fields,designed by Gibbs, is rather curious. The entire breadth ofthe building is 69 feet, which is divided into 3 parts, the navemeasuring 40 feet, and the remaining 29 feet being dividedbetween the two aisles. The central portion is covered by