It jLHwardattheirfeetadis

tance of eight inches in the short length Fig. 78. of the timber between hitcham, roof of nave. the collar-beam and

True double hammer-beam type. Late iGth century. Length 48 ft.

"... Throughout the whole roof . . . the dropping of the hammer-beams, the distortion of the hammer-posts, and the springing of the principal rafters, are considerable."

Sir Frank Baines has kindly furnished two photographs of the Eltham Palace, roof, taken while the work of restoration was in progress. In the latter, the. steel reinforcements to each truss may be noticed, and some idea formed of the defective state of the roof. ■ This photograph is unique, being taken while the tiles were temporarily removed, thereby allowing of the entry of light from above.

Fig. 82 shows the fine roof of the Middle Temple Hall, of the double pendentive

Hammer Beam Roof

EARL STONHAM, SUFFOLK. ROOF OF NAVE.

EARL STONHAM, SUFFOLK. ROOF OF NAVE.

Single hammer-beam, alternate pendentive type (c. 1460). Span 17 ft. 6 ins Length 68 ft. 3 ins.

hammer-post type. This is a late example of a timber roof of this kind, dating, as it does, from the years between 1562 and 1570. It is a Renaissance, rather than a Gothic, roof. It measures 100 ft. in length, 42 ft. in width, and with a height of 47 ft. Although the Hall building has the usual high pitch of roof, full advantage has not been taken of this fact, as in the earlier fifteenth-century manner. A central purlin has been fixed under the collars and boarded in above, giving the effect of a flat ceiling below the collar-level. This collar-purlin is reinforced by arch-braces to the lateral tie-beams, and the collars are stiffened by four turned queen-posts, two 011 each side of the archbracing.

The lesson of Eltham Palace has, evidently, been learned in the case of this roof of the Middle Temple Hall. It is pendentive only in effect. The hammer-posts, with their arch-braces, rest full on the hammer-beams, with separate pendentives below. The wall-posts are unusually long, thereby distributing the thrust well down on to the wall faces. Some restoration and renovation to the Hall has been necessary, at various dates, in 1G97, 1755, 1791 and 1S08, but much of the work at the earlier dates was in the nature of additions and alterations. The roof has survived with very few structural defects. It is not only rich in detail, but also sound in design.

In Figs. 83, 84, 85 and 86 we have, perhaps, the most remarkable church roof in England, in the otherwise insignificant church of Needham Market, not far from Ipswich. This is a true double-aisled roof, and a comparison of this with that of Harmondsworth Barn, Fig. 45, will show the same constructive principal. In Needham Market Church, however, the hammer-posts only reach to the beams, whereas at Harmondsworth they continue to the floor. This remarkable roof is built with a lantern, or clerestory, shown more clearly- in Fig. 85. The crown of the roof is really low-pitched, with a sharp slope below the clerestory windows to the wall-plate. Below the lantern or clerestory level, large cambered collar-beams are fixed, not from wall to wall in the form of true tie-beams, but between the vertical hammer-posts, a tenon three inches in thickness being taken through the hammer-post, with the principal rafter as an additional tie. The hammer-posts, which are of unusual height, are stiffened with longitudinal braced ties, and at the wall, above the large cornice, a principal ashlar-post corresponds with the hammer-post itself. Although, apparently, a pendentive hammer-beam, the pendants below are suspended, the hammer-posts bearing upon their beams instead of 011 tenons at their ends. Winged angels mask the junction of post and beam, but in Fig. 8() the projection of the hammer-beam beyond its post can be clearly7 seen, and also the distinct character of the pendant below

As an example of intricate construction, the roof of Needham Market Church will repay close study. The sectional diagram, illustrated in Fig. 84, will assist the comprehension of the principles on which this roof has been constructed. The low-pitched roof-crown has a certain nominal outward thrust in the direction A, but this can be ignored, as it is so small in amount. The direction of the downward pressure on the tall hammer-post, which is transmitted, via the hammer-beam to the wall-post, is indicated by the arrows at B B B. The tendency is for the hammer-beam to be depressed at its projecting end, the direction of which is shown by the arrows C- C. Such depression would cause the hammer-beam to pivot on the wall-post at I), thus exercising an upward pressure on its outer end, which would be transmitted to the principal rafter on the line E E, thereby effectively counteracting the downward pressure of the clerestory, via the hammer-post to the hammer-beam. The junction of the principal with the

0 0

Post a comment