Strip foundation query
Discussion
We have obtained planning permission for a first floor extension over an existing converted garage.
It all depends on the existing footings so I have dug a trial hole to find this
The walls are cavity walls and there is 450mm from ground to foundation.
The projection out is 250mm and concrete is 300mm thick.
What is the consensus?
It all depends on the existing footings so I have dug a trial hole to find this
The walls are cavity walls and there is 450mm from ground to foundation.
The projection out is 250mm and concrete is 300mm thick.
What is the consensus?
The brickwork below ground surface level nomaly counts as foundation also,so depth of concrete and bricks .
It might be that an inspector may think differently.
Could a timber framed extension be considered for lightness?
It took me a minute to work out the photo is the wrong way round.
It might be that an inspector may think differently.
Could a timber framed extension be considered for lightness?
It took me a minute to work out the photo is the wrong way round.
The building inspector will just state that he/she will happily receive the structural engineer's calculations. They may/may not agree with you on the soil conditions, or ask for a bearing test. You will need the structural engineer to work out the line load of the building and then see whether this exceeds the value for firm clay in BS8004. Firm clay is not the best for this at all at 75-150 kN/m2.
To give you an idea, I built a single story double skin cavity wall which was designed to be brick inner and outer. This with a lightweight metrotile and timber roof, insulation, snow loading and plasterboard, the foundations themselves etc. came out at 35 kN/m2 and my ground was characterised as firm clay. I had a strip foundation 480 mm wide.
If you're in the north west and want a structural engineer to do these calculations, I can recommend a friend.
To give you an idea, I built a single story double skin cavity wall which was designed to be brick inner and outer. This with a lightweight metrotile and timber roof, insulation, snow loading and plasterboard, the foundations themselves etc. came out at 35 kN/m2 and my ground was characterised as firm clay. I had a strip foundation 480 mm wide.
If you're in the north west and want a structural engineer to do these calculations, I can recommend a friend.
magooagain said:
The brickwork below ground surface level nomaly counts as foundation also,so depth of concrete and bricks.
No it doesn't. OP. You have 250mm projection, standard cavity wall is 350mm, therefore you have a minimum of a 600mm strip foundation. Which is pretty standard for housing. the important soil is what its sat on so if you haven't exposed that yet you need to dig some more and test that. Building inspector may be able to help you but I would imagine you should get a structural engineer out to inspect the soils and draw up some quick calcs showing the increase in bearing pressure.
Edited by fuzzyyo on Sunday 16th April 21:34
Looks a fairly good result to me.
Check - Minimum depth of foundations 450MM below ground tick.
Check - 150MM wider than wall (both sides?) tick?
Check - Minimum concrete thickness 200MM tick.
As long as the existing building is good and sound with no obvious structural problems then should be good to go. Get a structural engineer to look it over, £2-300 max.
PS I am a builder!
Check - Minimum depth of foundations 450MM below ground tick.
Check - 150MM wider than wall (both sides?) tick?
Check - Minimum concrete thickness 200MM tick.
As long as the existing building is good and sound with no obvious structural problems then should be good to go. Get a structural engineer to look it over, £2-300 max.
PS I am a builder!
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