Civil Engineering Reference
In-Depth Information
form of rooi ng was universal for domestic building and also was used in some
measure for monumental building.
h e reason that wood is the structural material for this type of rooi ng devolves
from the properties of matter. A member set horizontally across space will bend
downwards in the unsupported run, and this will stress the lower part of the mate-
rial in tension. h e only conveniently available building material which is strong
in tension is wood. h us it is that the load of a terrace roof must be distributed
through a wooden frame-work. h e construction of such a roof varies in details
but the system is constant. h e cladding is of earth (applied plastic) ot en with a
surface layer of more impervious earth/clay (which must be kept rolled). Below
this the structure consists of a continuous layer of reeds or matting (or both)
supported on more or less closely set wooden poles which span from wall to wall
(or where necessary are laid over beams). Such rooi ng, in spite of its defects,
remained unchanged in essence over great areas of the Middle East from Neolithic
times until the 20th century. It can be reconstructed in more or less detail because,
although the organic components (reeds, matting, poles) have generally decayed
completely, careful archaeological excavation and observation ot en reveal their
negative impressions let on adjacent earth or clay.
Very recently there has been some question of the ultimate antiquity of this
form of rooi ng. When the pre-pottery Neolithic Round House was recognised as a
beginning to solid building in the Middle East, it was apprehended that at er light
shelters of pliant woody materials the Round House form in mud brick or rubble
was roofed by corbelling the solid load bearing material into a beehive structure
as is the case with traditional modern round house building. Recently, however,
it has been asserted that such round house building of the 8th-7th millenium
BC were roofed with the l at mud brick terrace roof proper to the somewhat
later rectangular building. Perhaps the basis of this assessment lay in recognising
the impressions of poles and reeds etc. as small fragments of clay rooi ng from
round houses. h e interpretation of this was further troubled by a very trenchant
ambiguity in the use of the word “l at” in English. Flat, where apposite, is ot en
synonymous with horizontal (certainly so when describing a roof ), however in
general use it also connotes any plane surface as opposed to a curved or irregular
one, no matter what the angle to the horizontal may be. It is quite reasonable that
small fragments of clay rooi ng to prehistoric round houses were discovered with
a plane (not curved) surface, showing impressions of poles, reeds, etc. h is, how-
ever, does not mean necessarily that the fragments came from a horizontal roof.
It means that they came from a clay roof supported on a pole and reed frame, not
from a corbelled mud brick roof; and the contour of this roof was facetted conical
in nature rather than beehive.
Mud ter-
race
rooi ng
on wooden
frames
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