Fig 3.5 Examples of mud wall constructions.
Left: An early mud wall supported with uprights only. (Source: Huxley 1939) Right: Later mud wall construction at Riuki Cultural Centre using horizontal flexible wattle rods with nails (Source: Author, 2003)
This type of construction seems to be the more recent of the wall types with the oldest being the brushwood wall followed by the planks wall. A study of fig. 3.5 by Huxley (1939) shows the vertical poles supporting the mud without the longitudinal rods. This type of mud wall construction was documented by Routredge. “The walls are filled in with fine wattling, smaller uprights being introduced between the main uprights as required. When the hut has been completed this wall is daubed with clay” (Routledge, 1910).
In the latter system of supporting the mud, longitudinal rods were used to form a lattice. After the circle was marked, holes of a depth of up the elbow were dug all around the circle at about 18 inches apart. The vertical poles were then connected like a grid with horizontal flexible thin rods, at intervals of about a foot both inside and outside. They were tied firmly to the poles by using the bark of the mugiyo or any other tough but flexible bark. The gap thus created, kirigo, was filled with fresh mud prepared in a pit nearby. Once the mud was in place until no timber could be seen the women clawed it with their fingers to create groves that would later take the cow dung and ashes mixture that would be the final finish. This latter finish was put in place after several days when the mud had completely dried and gaps created by the drying mud had been filled. Later nails were used to fix the horizontal rods to the vertical posts. The construction
of the roof and the interior layout was the same as for the planks construction.
This kind of construction is still visible in Mukurwe-ini and the details are shown in fig. 5.78
3 . 6 . 0 R O O F C O N S T R U C T I O N
Fig. 3.6 A missionary visiting with a family in front of their Nyumba. (Source: Cagnolo, 1933)
Roofs varied greatly in thickness. This is explained by the fact that as the Nyumba grew older more grass kept on being added on top of the old grass just before the rainy season, so that it was a fairly easy way of also telling the age of a house. I have been informed that thicknesses of more than one foot were not uncommon.
Fig. 3.6 above is a roof of a Nyumba at the beginning of the Twentieth Century in Kikuyuland. Whether the supporting wall was made of brushwood like in the picture or whether they were planks or mud construction, the roofs were constructed in the same way. The main construction issue that the above picture raises is just how such a heavy roof could have been supported by such thin rafters - visible under the thatch - of 1.5-2 inches diameter. The Kikuyu did not construct trusses and most importantly, there was no central pole because the fire had to be at the centre and other spatial requirements that we will see later.
The internal diameter of the inside excluding the overhang porch could vary
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between 15 and 20 feet depending on the wishes of the owner (Leakey, 2007).
The rafters also had to bear the weight of 3-5 women who did the thatching. It is therefore important to understand the structural mechanism involved.
Fig 3.7 Cone construction with hoops (Source: Routredge, 1910)
First we must understand how a cone is constructed. The easiest way to construct a cone is to have all the rafters of exactly equal lengths starting from a circle meet at the centre. The meeting point at the apex of the rafters can be to an apex pole, or they are tied to each other while being supported temporarily with an upright pole. Since they cannot all fit at a point you will have to make do with at least four of them and then construct a hoop tied firmly to the four main rafters at a lower point to take more rafters of again equal length. Another hoop to take even more rafters lower down may be required as the diameter of the cone gets larger and larger. These hoops when tightly tied to the rafters also stiffen the cone preventing it from collapsing by taking most of the outward thrust exerted on the circular wall. The circular wall is also finished at the top with a hoop making the wall act as a uniform cylinder, a very strong structure.
The fixing of each rafter to a wall plate hoop has to be perfectly firm to prevent slipping. The central pole assisting the rafters’ connection to each other at the apex can then be removed as the cone is self-supporting.
The Kikuyu used eight primary rafters, miratho, as the main structure for the cone and two hoops, mbara on the underside of the rafters. An unspecified number of secondary filler rafters, miitiriro, went to reduce the spacing. As a provision for the attachment of the thatch, flexible rods were now tied
horizontally on the upper side of the primary and secondary rafters at intervals of about 18 inches so as to form a grid upon which the thatch was to be placed.
Routredge (1910) was the first to document the two hoops though he gave no indication in his drawing that all the rafters could not all meet at the apex (Fig.
3.8). These rods and the hoops were made from stems of the creepers mutanda mbogo, (Scutia myrtina), mugukuma, (Keetia gueinzii) or thin branches of the
mukuyu, (Ficus sycomorus) (Leakey, 2007:143). The rafters were made from the muyuyu, (Chaetacme aristata), muhethu, (Treama orientalis) or mutundu, Neoboutania macrocalyx) (Leakey, 2007:139).
Fig 3.8 Roof construction. (Source: Author 2011 after Leakey 2007)
Construction drawing by Leakey showing the strengthening hoops for the wall cylinder and the cone. The columns forming the square support the rafters internally. The rafters at mid‐point of the square are supported internally by the arched rafters, miikio.
All this presupposes very strong and heavy rafters and as has been observed, they were actually very thin roughly 35-75mm in diameter. These would have collapsed through bending even without the splaying and so there was another support system supplementing the hoops.
The first four of the main trusses, miratho were supported by a set of four twin columns forming a perfect square inside the circle. This square is the key to understanding the space layout of the Nyumba. (Fig. 3.8,13) It is also the key to the structure. Eight more columns, two on each side of the square were fixed to support the other four main rafters. Here an interesting thing happened. The
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columns on each side of the square are evenly spaced and yet the rafter is falling at the centre of the side of the square. An arched flexible rafter (most of them were green and still flexible) was made flying from one corner of the square to the next. At the top of the arch the secondary rafter was supported. This innovative arched rafter was called muikio, (a thrown).
All over Africa, these kinds of innovative structures are still very prevalent but are fast being replaced by unimaginative expensive structures. A lot can be learnt from these traditional engineers and craftsmen.
Fig. 3.9 Roof support systems from various parts of Africa.
Top Right: A Teso house in Uganda showing the use of the hoop for both support and shape of the cone. The form is arrived at through a careful adjustment of the diameter of the various hoops.
Bottom Right: The underside of a Fulani cone showing complex manipulation of the hoops (Source: Denyer, 1978)
Architects and modern cultural artists who make paintings with traditional scenes usually draw the Kikuyu Nyumba as nice geometrically perfect and straight lined cones whereas they looked like organically well worn and fitting hats or as Huxley (1960) more accurately likened them to - mushrooms (Fig 3.11). The roof slope was not a straight line either. The slight rise of the roof at the wall level and the dip between the inner pole and the apex can be explained by the fact that the thin and flexible rafters are held down firmly at the eaves end and the substantial distance between the inner poles and the apex. Of note is that the roof slope was very low at approximately 30-40 degrees according to Routredge (1910). Another point that is usually missed in the various
descriptions of these structures is the fact that ground line of the floor was not an even straight horizontal line. The splash of the water from the roof combined with the almost daily sweeping of the bare earth compound eroded the compound level and the daily sweeping of the inside also eroded the inner level leaving a plinth that was high and dry. The daily traffic of goats also did much to add to the erosion. At the threshold of the Nyumba, it was necessary to take a step down of 6 inches to one foot and this simple level difference created a much bigger roof clearance on the inside. Even though one had to bend almost double at the door as described so graphically by Cagnolo and others, one was able to straighten up when inside. As a youth I used to take milk to my older mother, maitu mukuru, and I remember these details in her traditional Nyumba. What is unforgetable is the powerful distinctive aroma of the thatch and the smooth shiny blackness and darkness pressing in on the fireplace making it a place of awe. The extent of the plinth was marked by the drops of water from the roof. This area also received the soil from the daily sweeping of the Nja and the ashes from the fireplaces and therefore grew higher than the inside and Nja level.
Fig. 3.10 Section through Kikuyu Nyumba showing the changes in levels. (Source:
Author, 2011)
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Fig. 3.11 Kikuyu homestead (Source: Routredge, 1910)
Water color rendering by Catherine Routredge. Note the low roof and deep overhang leaves the wall well sheltered from the elements.