

Fig. 13. 



R I 



TABLE II. PLATK CCCC LXXXI. Fig. 10. 



117 





In the roof represented in Fig. 10, the principal rnf- gainst the end of the straining beam S, from being Fig. 10. 

 - I' an- exposed to no cross strains a? each purlin notched and bolted together in pairs at each joint. By 

 C i> supported ; nntl the points of support divide the this means the sagging is avoided which generally 



m into three bearings comparatively short. 



At the side marked D of the Injure, and above D, 



the end of the principal rafter 1' is made to abut a- 



rs from the sinking of the heads of the queen 

 posts. 



TABLE III. PLATE CCCCLXXXI. Fig. 11. 



Fig. 11. 



The roof shown in Fig. 11 has the advantage of 

 leaving much free space in the middle. For spans of 

 this width, the tie-beam should be scarfed between a 



and b. The middle of the tie-beam may be strength- 

 ened by bolting to it the straining sill s. 



TABLE IV. PLATE CCCCLXXXI. Fig. 12. 



: Fig. 12, 



In the roof shown in Fig. 12, the straining sill s 

 should be tabled or keyed, and should be bolted to the 

 tie-beam in the manner represented in Plate CXXVII. 

 of CARPENTRY, Fig. 2, No. 2, and described in p. 534. 

 This roof resembles that of the Birmingham theatre, 

 described with the scantlings and timbers, in NICHOL- 

 SON'S Carpenter's Assittanl, p. 6'1, Plate 73, 2d Edition. 



TABLE V. PLATE CCCCLXXXI. Fig. 13. 



By reducing the upper part of the roof to the same 

 form as in Fig. 11, it would answer for a span of from 

 60 to 75 feet, the scantlings being as in the above table. 

 The roof, however, exhibits too great an expanse, and 

 it is not easy to light the large space in it. Under 

 these circumstances, an M roof is preferable. See Ta- 

 ble VI. 



TABLE VI. Scantlings for M Roofs. 



PLATE CCCCLXXXI. Fig. 14. Fig. 14. 



In this roof the trusses are ten feet apart, and the 

 pitch is the same as in the preceding table. 



This roof is from PRICK'S British Carpenter, and the 

 scantlings from Mr. Tredgold's work. Mr. TredgoKl 

 remarks, that it would be better to make the top flat, 

 and cover it witli lead, and adopt the truss in Fig. 1 2, 



