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Question for a4architect
Rank: Veteran Joined: 12/8/2009 Posts: 975 Location: Nairobi
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a4architect.com wrote:nakujua wrote:On the septic tank issue, I am starting on putting up a house somewhere on kangundo road and I asked a 'foreman' (that's what he called himself) for a quote ya septic tank, which I was intending to start with - but he shocked me when he told me a good septic tank will cost me between 500k - 800k.
The same quoted a figure of around 400k for the house foundation, anyway I will start na nyumba kwanza, I will worry about the septic latter.
To those in the know, I was told kuna ndarugu ngumu na soft with a quote of around ksh 16 for the soft and ksh 44 for the hard - can anyone confirm. please. @nakujua, like i said above, most kenyans do not get good septic tank designs so they end up being mis advised to build huge gigantic tanks that cost around kes 500k. Its not the size that matters, its the design. A septic tank costing kes 80 to kes 120k construction cost will perform more efficiently than a 400 to 500k gigantic tank. For anaerobic respiration to take place, it needs warmth and lack of oxygen, which cant be found in a huge tank. Without warmth and oxygen, the waste cant be biodegraded into liquid, hence filling up within months and causing blockage. Talk to a certified civil.structural engineer for a good drawing then thank me later. @A4 As always thanks! Now it seems like I have to go back to the structural engineer. I was trying hard to minimize his costs  FYI I was given a quotation of about 200 k for a septic tank with a soak pit (sp). It is to serve about 15 no 2 BR units. You will know that you have arrived when money and time are not mutually exclusive "events" in you life!
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Rank: Elder Joined: 3/19/2010 Posts: 3,505 Location: Uganda
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any advantage of using bamburi cement which is more expensive than the rest? ama simiti ni simiti punda amecheka
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Rank: Veteran Joined: 1/4/2010 Posts: 1,668 Location: nairobi
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structural engineers who do numerous concrete strength cube tests can update us on this i.e whether these new cement brands are within the tests for the same mix as Bamburi. On paper, they are all 32.5kn/mm2 strength and i hope KBS usually does regular testing to prove that whats specified on the cement package is actually what's being sold. Private structural engineers and KBS should be in a position to clarify this. As Iron Sharpens Iron, So one Man Sharpens Another.
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Rank: Elder Joined: 12/17/2009 Posts: 3,583 Location: Kenya
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@a4architect,
Something that has been on my mind, I have read a few articles online just needed some clarification.
In areas with black cotton soil that is not very deep, most people prefer to excavate the whole lot and fill in with some other soil - whats the importance of this vis a vis digging wider trenches and lining the foundation walls with some other soil.
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Rank: Veteran Joined: 1/4/2010 Posts: 1,668 Location: nairobi
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@nakujua, black cotton soil affects the slab by expanding and contracting hence cracking the slab. There will be no effect if you only excavate and back fill the trenches since the effect is only felt mostly at the centre of the slab. As Iron Sharpens Iron, So one Man Sharpens Another.
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Rank: Veteran Joined: 8/25/2012 Posts: 1,826
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a4architect.com wrote:@nakujua, black cotton soil affects the slab by expanding and contracting hence cracking the slab.
There will be no effect if you only excavate and back fill the trenches since the effect is only felt mostly at the centre of the slab.
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Rank: Elder Joined: 12/17/2009 Posts: 3,583 Location: Kenya
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a4architect.com wrote:@nakujua, black cotton soil affects the slab by expanding and contracting hence cracking the slab.
There will be no effect if you only excavate and back fill the trenches since the effect is only felt mostly at the centre of the slab. Hope you do not mind if I engage you further on this, if black cotton soil only affects the slab (not sure, but I am assuming a house load is borne by the foundation not the slab) - would there be any consequences apart from the slab cracking, to a house sitting on a non excavated black cotton soil lot. (also assuming its not suspended)
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Rank: Veteran Joined: 4/4/2007 Posts: 1,162
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nakujua wrote:a4architect.com wrote:@nakujua, black cotton soil affects the slab by expanding and contracting hence cracking the slab.
There will be no effect if you only excavate and back fill the trenches since the effect is only felt mostly at the centre of the slab. Hope you do not mind if I engage you further on this, if black cotton soil only affects the slab (not sure, but I am assuming a house load is borne by the foundation not the slab) - would there be any consequences apart from the slab cracking, to a house sitting on a non excavated black cotton soil lot. (also assuming its not suspended) Many consequences: The walls may crack and this will become worse with every wet - dry cycle of weather: this will further cause doors and windows not to shut properly, the structure may also tilt
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Rank: Elder Joined: 12/17/2009 Posts: 3,583 Location: Kenya
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majimaji wrote:nakujua wrote:a4architect.com wrote:@nakujua, black cotton soil affects the slab by expanding and contracting hence cracking the slab.
There will be no effect if you only excavate and back fill the trenches since the effect is only felt mostly at the centre of the slab. Hope you do not mind if I engage you further on this, if black cotton soil only affects the slab (not sure, but I am assuming a house load is borne by the foundation not the slab) - would there be any consequences apart from the slab cracking, to a house sitting on a non excavated black cotton soil lot. (also assuming its not suspended) Many consequences: The walls may crack and this will become worse with every wet - dry cycle of weather: this will further cause doors and windows not to shut properly, the structure may also tilt sawa, thanks. the other day some fundi was trying to talk me into it but I brought along the architect who insisted on going the excavation / filling route since the depth of the cotton soil is around 2 feet. I am just trying to get my head around the whole concept, if you keep the foundation plus the walls away from the black cotton soil, the only point of contact between the cotton soil and the walls would be the slab - would reinforcing the slab with some steel then prevent it from being moved by the soil underneath.
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Rank: Veteran Joined: 4/4/2007 Posts: 1,162
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nakujua wrote:majimaji wrote:nakujua wrote:a4architect.com wrote:@nakujua, black cotton soil affects the slab by expanding and contracting hence cracking the slab.
There will be no effect if you only excavate and back fill the trenches since the effect is only felt mostly at the centre of the slab. Hope you do not mind if I engage you further on this, if black cotton soil only affects the slab (not sure, but I am assuming a house load is borne by the foundation not the slab) - would there be any consequences apart from the slab cracking, to a house sitting on a non excavated black cotton soil lot. (also assuming its not suspended) Many consequences: The walls may crack and this will become worse with every wet - dry cycle of weather: this will further cause doors and windows not to shut properly, the structure may also tilt sawa, thanks. the other day some fundi was trying to talk me into it but I brought along the architect who insisted on going the excavation / filling route since the depth of the cotton soil is around 2 feet. I am just trying to get my head around the whole concept, if you keep the foundation plus the walls away from the black cotton soil, the only point of contact between the cotton soil and the walls would be the slab - would reinforcing the slab with some steel then prevent it from being moved by the soil underneath. It can work but remember: water bonds chemically with the black cotton soil thus the change in properties, it can heave/shrink up to 14% in all directions and therefore keeping water out of the clay might be the big job
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