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< prev - next > Construction Earth construction woodless construction 3 (Printable PDF)
Woodless construction: change and adaptation to local needs
Practical Action
Ongoing technical changes
Using local brick sizes and laying methods
First introduced to Niger in 1980, during the next decade brick dimensions and bonding patterns for
woodless construction used quite complex bond layouts with bricks laid as headers and stretchers -
an often complex bonding pattern that acted as a brake on the assimilation of the techniques. To
simplify building, and following common local practice, brick laying was then changed to "headers
only" for the majority of small buildings, and adopted two main wall brick sizes one measuring 38 x
24 cm, the other, 40 x 19 cm, both used in walls that are about 40cm thick (enough for a small
domed or vaulted structure). These dimensions gave good results and remain popular today. A
further step was to eliminate the need for cutting bricks to fit given metric measurements, which
could result in poor bonding along a wall. Woodless Construction therefore adopted using the brick
itself as the unit of measurement. This enables the laying out of the buildings to be based firstly on
approximate metric dimensions and then laid out precisely on site in terms of an exact number of
bricks and joints, an approach that takes account of local variations in brick sizes. Indeed, where the
size of the local wall brick is adequate, today the programme accepts that local brick sizes can be
used, provided a good brick bonding can be achieved.
The brick saw: using the brick as a unit of
measurement does however create
potential conflict with inserting ready made
joinery. One answer has been, when
necessary, to build the width of openings a
little smaller than required, and then to
use a wire "mud brick saw" to trim the
opening to the desired size. This avoids
making unsafe adjustments to the bonding
pattern in the wall.
Drawing the vault
Nubian vaults in Upper Egypt were
traditionally drawn by eye or in some cases
with a template. Sahelian builders found
accurate drawing of the vault by eye diffi-
cult to learn and the use of a template
unwieldy and impractical since it was
difficult to move from one location to
Figure 4: Vaults are drawn based on 1/3 of the span
another. For the Sahel builders a method
has been developed that is based on using
wires and on the subdivision of any vault
span into three equal lengths, which is
achieved by folding into three a length of wire equal to the span. Based on this ‘one third of the
span’ length, three equal length wires are joined at a common point. Two nails are placed at spring
point level into the end walls of vaulted rooms at one and two third intervals, to which the end of two
of the wires is attached. The builder can then quickly and accurately draw the curve of the vault. The
vault shape is not only close to the catenary pure compression shape (the pure tension form of an
inverted suspended chain) of the Nubian
vaults, but in addition this slightly new shape
has a more accentuated curve that
compensates for the loading over the sides of
vault produced by infilling the valleys in the
Keeping the vault alignment right
Nubian vaults are usually built out from one
end wall, against which they lean. To help the
Sahel builders keep a straight alignment, an
early innovation has been the practice of
Figure 5: Guiding strings help builders maintain
3 the alignment of the vaults.