V.6.1
ROOF CONSTRUCTION:
ASSEMBLAGE OF THE SUPPORTING
FRAME OF TIMBER
The aisled and timbered medieval barns and houses discussed
in the preceding pages give us a fairly good idea of
the kind of carpentry we might expect to have been employed
in the guest and service buildings of the Plan of St.
Gall. Although we could identify two distinct classes of
roofs, we found that the roof-supporting trusses were of
very similar design in both cases. In the majority of buildings
the arcade plates from which the rafters spring were
tenoned into a recess in the head of the posts. The tie
beams were laid upon this assemblage from above and
were locked into the posts by means of mortice-and-tenon
joints, into the arcade plates by dovetail joints (fig. 356).
One building only, the Barn of Great Coxwell, Berkshire,
departed from this rule by putting the plates on top of the
tie beams (fig. 357). We have chosen the more common
form of Chichester (fig. 356) and Parçay-Meslay (fig. 354B)
as the standard form for our reconstruction of the post-and-plate
assemblage of the houses of the Plan of St. Gall.
The bracing beams were either straight, bent, or curved;
sometimes long, sometimes short; sometimes single, sometimes
double; but in all cases of relatively heavy scantling.
We may safely assume that all of the simpler variants of
this group were in use in Carolingian times, excluding such
types, of course, that owed their design to influences from
Romanesque and Gothic masonry architecture, such as the
round arches of Hereford Palace (fig. 340) or the Gothic
arches of Nurstead Court, Kent (fig. 345) and Little
Chesterford, Essex (fig. 348).
From the side of the aisles, the principal trusses were
steadied by aisle ties, tenoned into the freestanding posts
on the level of the wall head. The outer ends of these ties
served as springing for inner rafters of heavy scantling,
running parallel to the roof slope, a short distance inward,
and butted into the heads of the principal posts some two
or three feet below the arcade plate. On the wall side these
aisle ties rested either on two parallel courses of wall plates,
one running along the outer, the other along the inner edge
of the wall head, as in Great Coxwell (fig. 350B); or they
were tenoned into the heads of posts set against the long
walls on the inside, a method by means of which the timber
frame was, structurally, held virtually independent of the
masonry walls, as in Parçay-Meslay (fig. 354B). In buildings
constructed entirely in wood the post-to-plate assemblage
of the outer walls would, of course, have been a repetition
on a smaller scale of that of the principal posts and the
arcade plates (as in the barn of Little Wymondly, discussed
below, fig. 434). In reconstructing the St. Gall outbuildings,
we have chosen freely, from among all these different possibilities,
whatever the condition of a particular building
suggested as the most logical solution.
