Ground below beam and block floor

[an203888]

I am just sorting the ground out before installing the beam and block floor on my extension. Instructions from beam supplier just say all vegetation should be stripped (it was a patio before so no vegetation anyway) and obviously a 150mm void is needed.
So I am just levelling what I have... Lots of old bricks etc as it was made up ground. Anyone see any issues with this?

IMG_20200307_154010

• an203888
• 7 Mar 2020

 

[^woody^]

That topsoil looks good enough for carrots and collies, not block and beam.

 

[an203888]

That topsoil looks good enough for carrots and collies, not block and beam.

Sorry woody, can you elaborate little please? The other two 'sections' are all Sand but this one closes to camera isn't. But it's 6 inches lower than the other two. I was planning to add a thick weed membrain to all and then cover this closes end with sand?

 

[^woody^]

Topsoil is vegetable matter, things will be growing in it. A weed membrane is to stop seeds entering the top of soil, not coming up through soil.

You need to be confident that nothing will be growing up from it, and that it won't be smelling of rotting organic matter.

 

[an203888]

Topsoil is vegetable matter, things will be growing in it. A weed membrane is to stop seeds entering the top of soil, not coming up through soil.

You need to be confident that nothing will be growing up from it, and that it won't be smelling of rotting organic matter.

That topsoil has been sat under the patio and with all the infill rubble since 1972 nothing has grown there for almost 50 years...presumably nothing will grow from it... Certainly no organic matter in it..

To remove it all I will have to go down roughly 1 meter. Foundations were 1.5 so I'm just not going to dig att that out... It was the whole point of the beam and block in first place... Because of the made up ground. What should I do?

 

[an203888]

Bump.... anyone else know?

 

[williamglossop]

What about some geotex and 50mm of oversite concrete.....

 

[an203888]

What about some geotex and 50mm of oversite concrete.....

Yep I could do that but still not really sure what BC are looking for etc and 50mm oversite us a lot of work if it's nit required. Some people seem to just have bare earth, some just put some hardcore on top, some put a membrane and some put an oversite on. Very confusing. Think I'm going to speak to BC tomorrow. Thanks

 

[Leofric]

50mm oversite concrete.

 

[an203888]

Just looking into the 50mm oversite option. The only issue I see is that the oversite will be at least 150mm lower than the outside ground level and have read that a permiable membrane plus gravel is a better option in this case. Either that or add a drain into the oversite which seems way ott.

 

[Leofric]

Just looking into the 50mm oversite option. The only issue I see is that the oversite will be at least 150mm lower than the outside ground level and have read that a permiable membrane plus gravel is a better option in this case. Either that or add a drain into the oversite which seems way ott.

Why can't the top of the oversite concrete be at external ground level then ?

 

[an203888]

Why can't the top of the oversite concrete be at external ground level then ?

Because that would bring the level of the oversite too close to the concrete beams... They need 150mm gap

 

[Leofric]

Yes ,I know you need a 150mm void under the floor beams but you make the finished floor level to suit

 

[an203888]

Yes ,I know you need a 150mm void under the floor beams but you make the finished floor level to suit

I'm sorry I don't understand. External floor level is 150mm below my internal, finished, screeded floor. Below my floor I will have 75mm screed, 100mm insulation (I'm now 25mm below external floor level), 150mm beam and then 150mm void so in total my proposed oversite will be 325mm below external floor levels... How can I possibly change that?

 

[Leofric]

What do you mean by external floor levels Presume you mean external ground level, but in that case why are you going for a beam and block floor instead of a ground bearing concrete slab which wouldn't give you these problems
ps just noticed you mentioned earlier about 'made up ground'