Foundation measurements and material required

Question

Hi, 

I am looking at doing a side and back extension. Side extension would be a double storey while back would be a single storey. I need advise on how deep and wide should the foundation trench be,  do i fill the trench to the top with concrete, if there are different types of concrete what type should i use,  and  do i need to place a steel mesh into the trench? 

My neighbour is also planning to do the side extension so can we dig a single trench between us and use that as foundation for both side walls? His house is on a slightly higher ground (10-20cm). Is it wise to have a gap between neighbours side wall and my side wall (we thought 10cm on each side of the boundary line hence leaving a 20cm gap) or is it better to build walls as close as possible? 

Your advise will be very much appreciated. 

Thank you in advance for your help.

Kind regards

Tom · Answer

Ground soil type will determine this and Building regs. will be able to advise in the width and depth of the foundation required. Clay soils need a deeper foundation.
Use a standard trench foundation concrete and do not fill to the top of the trench as this will be visible and ugly at the end of the build. Instead, use a class A or B engineering brick for brickwork below DPC. 
You can share the wall with your neighbour and this is common practice.
If you leave a gap between the walls then this space is lost and it is not needed anyway.

Javaid · Answer

There are many factors that determine the depth and type of foundation you need. This has to be calculated by a structural engineer and drawings have to be made and submitted to the local authority building control. Ultimately the building control inspector is the person who will decide the depth etc depending on ground conditions once you have reached at least 1m in depth.

Christopher · Answer

Hi if you're doing a single extension or double the trench for the footings should be 600 wide by min 1m depth but that depends if the ground is good but if it's made up of coal seem or trees nearby you will need to go deeper. You can mass fill with concrete as long its got some ground covering it .no you can't share the foundation with next door it's better to do your own and id advise you to leave a gap between each build. Your welcome regards Chris

Nicholas · Answer

Hi we done one very similar, the fittings were 600mm wide x1m deep filled with 600mm mass concrete as per building control request. Also, it is not good to share foundation building control will not allow, no mesh needed but for peace of mind, it can be done. You cannot build on neighbour foundation

Foundation measurements and material required

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