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Footings.
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The saga of ny garage rebuild continues, after knocking it down and cutting away at the slab I have now discovered that the base is 2 inches of concrete (grano), the wall is going to be single skinned and 2.3 metres high accomadating 2 double glazed windows and a door.
This base seems rather thin to me, so I'm wondering, do I need to dig out the slab for the boundary and make the footing deeper?
This base seems rather thin to me, so I'm wondering, do I need to dig out the slab for the boundary and make the footing deeper?
Answers
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No strip foundation should be less than 150mm in depth.
As to whether it needs to be more depends on the width of the strip. If you are intending to work with, say, a 400mm wide strip, that should be OK.
The required width of the strip depends on the bearing capacity of the soil beneath, and the loading of the wall sitting on it.
As to whether it needs to be more depends on the width of the strip. If you are intending to work with, say, a 400mm wide strip, that should be OK.
The required width of the strip depends on the bearing capacity of the soil beneath, and the loading of the wall sitting on it.
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Garages less than 30 square metres in external area don't actually have to comply with Building Regs but I agree that it makes sense to construct foundations as if BR did apply.
What The Builder is talking about (and I eluded to it without trying to be too technical about it) is that one really has to claculate the loading per linear metre along the long side wall sof the garage. This means not only the force exerted by the bricks themselves, but also the weight of the garage roof resting on the top of the wall. It isn't a difficult calculation but it is beyond the 2000 words we get here. Then one digs down to see what's under the soil. Different subsoils have varying capacities to hold up weight put on them - the loading capacity. Soft clay and rich loamy soils are the worse - stony materials are better, hard rock is the best. Depending on what you find, depends how WIDE your strip should be - as it spreads the load more onto the subsoil below.
My comment about 150mm depth was the depth of concrete - not the depth of the whole foundation including broken brick below. You could get away with 100mm perhaps if you put reinforcement into the concrete. The concrete has to be able to act as a cast lintel in its own right, and 50mm depth is too little in my opinion in any soil.
What The Builder is talking about (and I eluded to it without trying to be too technical about it) is that one really has to claculate the loading per linear metre along the long side wall sof the garage. This means not only the force exerted by the bricks themselves, but also the weight of the garage roof resting on the top of the wall. It isn't a difficult calculation but it is beyond the 2000 words we get here. Then one digs down to see what's under the soil. Different subsoils have varying capacities to hold up weight put on them - the loading capacity. Soft clay and rich loamy soils are the worse - stony materials are better, hard rock is the best. Depending on what you find, depends how WIDE your strip should be - as it spreads the load more onto the subsoil below.
My comment about 150mm depth was the depth of concrete - not the depth of the whole foundation including broken brick below. You could get away with 100mm perhaps if you put reinforcement into the concrete. The concrete has to be able to act as a cast lintel in its own right, and 50mm depth is too little in my opinion in any soil.
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