Steps in laying of a building foundation in Kenya

Laying the foundation of a building is done after the survey of the plot has been completed. The survey beacons will show    the physical boundaries of your property. The site to be covered by the building should then be cleared of tuft and vegetation matter. The contractor and Masons should then accurately determine corners of the foundation and use four short thick sticks that have been sharped on one side to physically mark each corner identified. Use the hammer   to fix the sticks deeply into the ground in such a way that they should describe square   at each of   the corners   of the building. Then determine the width of the trenches for the walls. Using  this  width the Mason strings two  lines  from one corner  to  the next, till the whole  building  is covered  and  in accordance  with building drawings. The width between the lines should be slightly greater than the width of the wall   of the proposed building. Using  these  lines  as  a guide ,the Masons  and  laborers  should  begin digging   the foundation trenches. This should produce straight   trenches   that in turn will facilitate the mason to construct straight wall   and in general building with accurate bearing and proportion. In short a structurally sound structure.

Special care should be exercise to ensure the building is in the right place on the plot and that all load bearing walls have been identified   and set out accurately on ground. Some of the tools used are measuring line and a square, in order to get the corners of the building right. The result is correct   orientation of the proposed building    with say the drive way, garage, stairs and balcony in right places

According to the Kenya building  code  of  1997 , “the foundation should  designed and constructed in such manner as to  sustain the dead  load of  the building  imposed  vertically  and laterally  and  to  transmit  these  loads to the ground in such manner  that the pressure may  not impair the stability  of  the building or adjoining  structures. In addition foundation laying should also factor into the equation the effect of wind on the building. Also it should be taken down in such depth that will safeguard the building from swelling, shrinking or erosion of the subsoil.”

Excavation

This entail digging the foundation trenches. The depth of the trenches will depend on the type of soil and slope of the construction site. Black cotton soil, clay, Alluvial, sand and red soil    are considered weak and will require deeper trenches that go past its substrata.  Also  a sloping  landscape  will necessitate  deeper  foundation trenches  to  be  dug  out.

Good soils with  hard  surface  that require standard or  shallow depths for the trenches are Compact Murrum soil, Compact gravel, compact Magadi soil, brown shale, Coral, and Nairobi stone soil.

The point is that the foundation should rest on a solid base beneath the ground. Remember not to misuse the soil dug out because it can be used to fill the foundation base.

Pour Concrete

Depending  on whether  the building  standard  house  or storey building   ,the concrete is  poured  in the  trenches  up   desired  height.

For Storey buildings, the mason will install ribbed steel bar   squares for all the corners of the building and then the concrete is poured and spread in and around them. Also the mason may lay Y 16 ribbed steel bars in the foundation trenches. All  these  is  done  to add  strength to the foundation and  enable it to   hold  together  the base  as one compact  unit. Once this done, concrete is poured and spread in the trenches to desired height.  Once the concrete has cured, lay the foundation stone and allow the masons the go ahead to build the foundation wall/stem wall.

Foundation base

Use soil to fill the foundation base before pouring in hard-core stones. This should then be covered by Murrum to create an even and smooth surface.

When the foundation is at the desired level and flat, prepare to pour a slab on it. To  improve the durability  of the  building   apply  anti termite  solution and anti –damp  material  to  make the  foundation water  proof.

During  pouring the  slab , call  in the plumber  to  install  water  and  sewerage  piping  .Also  an   electrician can be  called  to  install  necessary    electrical  wiring  conduits  before the slab dries  up.

©copyright East Africa Little hardware ltd 2017

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