Cavity infill below DPC

[SBMS]

Hi

Foundations done and our block and beam floor is down. We are having EPS beads (standard masonry construction). There’s currently no cavity infill from top of foundations to top of DPC. Building control weren’t bothered but some people are telling me we should concrete infill (up to 225mm below top of DPC), in the event of ‘ground heave’.  Is this right?

 

[joe90]

I did mine in XPS (similar to this) and I am on clay.

[PeterW]

+1 to what’s above and did 150mm fill with EPS beads. 

[SBMS]

9 hours ago, PeterW said:

+1 to what’s above and did 150mm fill with EPS beads. 

Thanks. Out of interest did you leave any airgap from top of concrete to the beads? We are probably going to put a cavity tray across the top but wondered if you can fill the beads all the way down to top of concrete infill?

[Iceverge]

We did this. Took the cavity 600mm below floor level and pumped full of beads. Didn't use any cavity tray either. Separate DPC in both leafs.

 

 

[SBMS]

17 minutes ago, Iceverge said:

We did this. Took the cavity 600mm below floor level and pumped full of beads. Didn't use any cavity tray either. Separate DPC in both leafs.

 

 

What were your ground conditions? We are on clay and worried about ground heave? I don’t know how strong beads down to foundations would be?

[Iceverge]

Compact sand and gravel here so no heave. 

 

We did have a 215mm inner wall so I guess that could be considered structural all on its own. Also we had I think about 3-4 courses of foundation blocks below the cavity. It wasn't built directly onto the poured foundations like the above diagram.

 

If you can assure drainage to a lower plane a French drain would help regulate soil moisture and prevent heave. 

 

 

 

 

 

 

[Miek]

On 05/07/2022 at 20:10, SBMS said:

Hi

Foundations done and our block and beam floor is down. We are having EPS beads (standard masonry construction). There’s currently no cavity infill from top of foundations to top of DPC. Building control weren’t bothered but some people are telling me we should concrete infill (up to 225mm below top of DPC), in the event of ‘ground heave’.  Is this right?

 

The reason for filling the below DPC cavity void is to resist potential soil pressure, it can be a very weak mix concrete. I used compacted type 1 with a concrete capping on a 300mm cavity. 

[JohnMo]

My stub walls are 365mm wide, consist of 150mm concrete blocks (inside), 100mm thermolite block (outside), 115mm void.  Void filled with 100mm PIR spray foamed into place.  To give me continuous insulation from the roof to below below ground and below my floor installation.  This with a 70mm upstand on the inside wall before screed should limit any sideways heat loss from the floor.

[Carrerahill]

On 06/07/2022 at 07:57, PeterW said:

+1 to what’s above and did 150mm fill with EPS beads. 

+2

[Carrerahill]

It should be backfilled yes.