Foundation question,

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pete121

Hello everyone.

I plan to build a single storey side extension, but plan to build on top in the future.

I need to know if 67cm of concrete is enough for a foundation fill. From the 67cm point of concrete there is 300mm upto outside ground level.

On the second wall foundation i'm leveled with 40cm of concrete, From the 40cm point of concrete i have 600mm up to outside ground level.

I was required to have foundations 1meter deep and 600mm wide. does this mean i must have have 1 meter in height of concrete? or i meter fron the outside ground level?

I have my doubts on concrete fill. I think its a little less. Can someone please help clarify.
 
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You can have full fill concrete if you like, many on here profess that it is cheaper than building up to ground level in block. The critical factor to satisfy Mr BC is the depth.
 
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pete121

Thanks mate, i dont want fill up to ground level, i would idealy like to have a few courses below. Going by the measurements ive given do they sound ok?

Can i fill a trench with only 40cm concrete and continue 96cm up with brick blocks?

The 2nd trench is 97cm from bottom of the trench upto my neighbors ground level.

The foundation guy has peged this trench 30cm down from neighbors ground level leaving 67cm for concrete fill in trench.

Its a single storey extension but i would like to build on top sometime later. I just need to be sure befor the guy fills it up.
 
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Sounds fine, but as mentioned you need to do it to the satisfaction of Building Control, they're who needs to approve it. If you want to build another storey on top at some stage, get Mr Building Control to approve it on this basis and try and get him to say he's happy with your future plans for the future in writing, take some photos with a tape measure too showing depths/width etc. That'll save you having to expose the foundation at a later stage.
 
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pete121

Thanks again mate, the bco has already been to inspect the work and has approved the foundations. Tbh his visit was'nt quite reassuring though.

The pegs were not in place at that time and neither did he inspect using a tape measure.

However i inspected them later in the day myself using a tape measure and noticed the width to be 500mm as to the required 600mm. I then widened them.
the depth was also a little short which i also fixed.

but only now after the pegging its transpired that the after leaving 4 courses of brick from the lowest ground level id be left with 67cm concrete fill, and in the other trench id have 40cm of concrete fill and 96cm up to dpc brick and blocks.

My main question is when a bco asks for 1meter depth and 600 width foundation does he want the whole 1000mm in depth filled with concrete?
so if i'd want four courses below ground level id have to dig 1.3meters down, filling 1 meter up with concrete and the other 0.3 with brick/block

Or is it 1 meter down from the external ground and and fill concrete/ brick/ block however you like. as long as its 1 meter down from external ground it doesnt matter how you make it up to dpc?

Also where should that 1 meter in depth be measured from? adjacent outside ground level?

Im more worried about the 40cm concrete.
 
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No it doesn't matter, you can do foundations about 200m thick with blockwork up to ground or deeper conc and just a single course up to ground, it matters not. Depth of foundation is from ground level to underside of concrete but varies depending on local ground conditions plenty of reading here: http://www.planningportal.gov.uk/uploads/br/BR_PDF_AD_A_2004.pdf

Beamlock-Foundations.jpg
 
P

pete121

Also having read some of you posts and taking note your abundant input on this forum i hope you could assist me with a little more then generic advice.

Changed it incase the word plethora meant offence.
 
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pete121

Cheers for that link, i think we were writing our post the same time hence i didnt see your response. I'll give it a read now and get back if uncertain about something.
Cheers mate.
 
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pete121

I have a further few questions i need clearing up, hope you can help.

1) so it is > 1 meter down from the external ground level and and fill concrete/ brick/ block however you like, as long as its 1 meter down from external ground it doesn't matter how you make it up to dpc?

2) Is there not even a minimum requirement for the thickness of the concrete fill?

3) Can you explain the underside of the concrete?

4) "Depth of foundation is from ground level to underside of concrete" don't quite understand this. Which ground level and what is the underside of concrete?

5) And another point of worry is if/when my neighbor has a similar extension, my side wall foundation would be exposed. His 1 meter of foundations will go past below my foundation as his ground is lower is this going to be a problem?
 
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1) so it is > 1 meter down from the external ground level and and fill concrete/ brick/ block however you like, as long as its 1 meter down from external ground it doesn't matter how you make it up to dpc?
Correct. However a 1m dig is merely a guideline. If ground conditions allow it can be less or if the ground is still not suitable at 1m then it may be more. Also nearby drains can influence the depth of the dig if said drains are deeper than 1m etc.

2) Is there not even a minimum requirement for the thickness of the concrete fill?
225mm (min) will deal with domestic extensions.

3) Can you explain the underside of the concrete?
Trench bottom.

4) "Depth of foundation is from ground level to underside of concrete" don't quite understand this. Which ground level and what is the underside of concrete?
Ground level is ground level usually 225mm below dpc or there abouts.

5) And another point of worry is if/when my neighbor has a similar extension, my side wall foundation would be exposed. His 1 meter of foundations will go past below my foundation as his ground is lower is this going to be a problem?
Not necessarily.
 
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5) And another point of worry is if/when my neighbor has a similar extension, my side wall foundation would be exposed. His 1 meter of foundations will go past below my foundation as his ground is lower is this going to be a problem?
If that happens the BCO should insist that the neighbour's trench would be filled with concrete to at least the bottom of the concrete on your foundation.
 

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