Ground below beam and block floor

[an203888]

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

Because the architect specified it... Reason being that we are on a bit of a slope and the ground we are building on is mostly made-up ground... Unsuitable for a normal slab.

Trust me... I would rather do a slab if I could!

 

[Leofric]

I see it a bit better now although the slope isn't clear , so what does the architect suggest

 

[an203888]

I see it a bit better now although the slope isn't clear , so what does the architect suggest

Architect has put 40mm oversite on drawing but this would leave potential for a build up of water as discussed. I have not mentioned this to him. Maybe I should just chuck oversite on it. I dunno.

 

[Leofric]

Discuss it with the architect and let them decide, that is what you are paying them for , to design your extension and specify a construction appropriate for the site conditions that complies with building regulations.

 

[^woody^]

Architect has put 40mm oversite on drawing but this would leave potential for a build up of water as discussed. I have not mentioned this to him. Maybe I should just chuck oversite on it. I dunno.

You need to be clear as to if you are working to an Architects generic specification or the beam manufacturer's actual installation instructions.

Typically a beam manufacturer will specify removal of vegetable matter (which is topsoil) then treatment with a weed killer, then some sort of membrane or polythene barrier, then either oversite or a thick layer of gravel.

The potential for build up of water is not there in the majority of cases, because water tables are not that high. The risk (ie a known risk, and not a risk read about on the internet) is only there if the plot is on a hill or suchlike, and in this case then that risk is dealt with by installing external drainage on the high level side. But as you have made up ground then drainage would be very good.

You also need to allow for insulation, as if you are insulating between the beams then typically the insualtion will go under a beam too to prevent thermal bridging

 

[an203888]

Spoke to BCO today who said he wasn't worried about a membrain or oversite as the ground is generally very sandy and drains very well. He just wants to see where the beams sit on the wall, air ducts and a 150mm air gap.

 

[Leofric]

Spoke to BCO today who said he wasn't worried about a membrain or oversite as the ground is generally very sandy and drains very well. He just wants to see where the beams sit on the wall, air ducts and a 150mm air gap.

a bit strange ,oversite concrete is to stop vegetation growing up under the floor Telescopic air vents will be required of course in your situation.

 

[bandejapaisa]

Looking at the street, concrete does not stop vegetation growing.

 

[martygturner]

a bit strange ,oversite concrete is to stop vegetation growing up under the floor Telescopic air vents will be required of course in your situation.

Err what vegetation grows in total darkness ? its a void, nothing will grow.

 

[phatboy]

Our engineers specified 50mm of blinding concrete. 4.5 tonne took 2 of us about 2 hours to barrow, spread and lightly tamp.

 

[bandejapaisa]

So the weeds can grow in total darkness, rise 150+mm, then work their way through 150mm beams or 100mm concrete blocks, which are bound with sand/cement,... then through the DPM, then through the 65mm of screed, and the wooden floor..... Engineers are suggesting this won't stop the weeds...

.... but 50mm gravel/concrete/blinding will.

 

[noseall]

We stoned our and laid 50mm concrete...

oversite1.jpg

• noseall
• 20 Jun 2023

oversite2.jpg

• noseall
• 20 Jun 2023

 

[bandejapaisa]

@noseall What's the black stuff he's putting down from the tin?

 

[^woody^]

@noseall What's the black stuff he's putting down from the tin?

Hair gel by the look of it.

 

[noseall]

@noseall What's the black stuff he's putting down from the tin?

Our BCO likes to have his input and insists that the floor beam ends are gobbed with bitumen paint - to inhibit rust I guess. The reinforcing rods are always exposed on the ends.