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-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 on 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 pcndentives 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 1697, 1755, 1791 and 1808, 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 on tenons at their ends. Winged angels mask the junction of post and beam, but in Fig. 86 the projection of the hammer-beam beyond its post can be clearly 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 D, 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 hammer-post is, really, the weak part of the whole construction, the strength of the latter being invalidated by the insertion of three tenons from the principal, the purlin, and the main tie-beam, the three-inch tenon of the beam being taken through the hammer-post to the principal at F. The small tie-beams, G, inadequate as they appear, are strong enough to correct any tendency in the hammer-post to bend in the lengthwise direction of the roof, which might occur owing to the enormous downward strain upon it, even when partially relieved by the upward pressure of the principal, carrying, as it does, nearly the whole of the superimposed weight of the roof.
Fig. 80. The Roof At Eltham Palace. - Pendentive type of hammer-beam. Early sixteenth century. - Photo by H.M. Office of Works.
Actually, in spite of the rake of the principal and the common rafters from below the clerestory down to the wall-head, there is little, or no outward thrust from this roof.
Fig. 81. The Roof At Eltham Palace. - Photo by H.M. Office of Works, taken when tiles were removed during the recent work of restoration to the roof.
Fig. 82. The Hall Of The Middle Temple. - 1562-70