width of foundations...

[matt73]

having single storey kitchen ext 5m wide by 3m. because of roots we may have to go down 1.5m not sure yet. we have a clay soil.

what would be a good width for the foundation. i was thinking 600mm just in case in future we would want to build on top. or would 450mm still be adequate for this.

if we decided it will only ever be single storey then will 450mm be more than enough.

should you employ structural eng to calcualte foundation sizes for a simple ext like this??

cheers

matt

 

[noseall]

b.c. like your foundations to have a 150mm projection either side of the wall, therfore 600mm will be the width of foundations as generally cavity wall thickness is 275mm and above

 

[Static]

In good clay soil 450mm wide footing will normally suffice for small 2 story unless you think your subsoil is poor quality or you intend putting concrete floors on at both levels.
Structural Eng will need more info about the soil/trees local to do a design but its a simple job.

 

[matt73]

cheers guys

 

[rangersman]

Also remember that a bricklayer will need to bring the sub structure up from the foundation level (1.5m deep) to GL - 600mm gives a bit more "working room"

 

[Static]

Normally works out cheaper the have the concrete footings top level higher (say 3 block courses below ground floor underside level) than have a bricky in a footing laying 1m of brick/blockwork, lets not even get started on health and safety working in deep trenches.