DPM and finsihed floor height for extension

[james Robert]

Hi all,

I'm doing the groundworks for my rear single story extension and just trying to get my head around the oversite preparation.

I've measured down from the existing floor level allowing for 150mm hardcore, 50mm sand, 75mm insulation, 100mm concrete and 60mm screed. When I do this, the finished floor is 2 brick course above DPC level. This means that the DPM is level with the DPC so am I right in thinking that I will then have to build another course of block up for the 100mm concrete slab? A lot of the images I've seen online seem to show the concrete layer being level with the DPC and using it to level off but if I did this, I'd be 150mm lower than the existing floor level.

Any advice would be greatly appreciated!

 

[noseall]

Either the proposed DPC is wrong or your existing is wrong. Are the existing floors timber by any chance?

 

[james Robert]

Yes the kitchen is timber floor. Can the DPC of the extension be set higher than that of the existing house? Maybe I need to come higher with my block work?

 

[^woody^]

The DPC goes at whatever your new floor level will be, irrespective of where it is on the existing house

 

[james Robert]

Brilliant thanks mate

 

[james Robert]

 

[james Robert]

So in the picture the top of the board is the finished floor level
On the right is a brick to show the line of the DPC matched against the same height of the old houses DPC
So I just build the new DPC higher so the concrete is below it?

 

[^woody^]

So I just build the new DPC higher so the concrete is below it?

The finished floor height is the height of the DPC - not below or above it. If you are just concreting then it's level with the concrete, if you are screeding, then it's at that height.

Work out the finished floor height, and gauge the brickwork down from that.

 

[james Robert]

Thanks woody it's the height of the existing DPC that's confusing me so I just need to forget that and work on the new levels. Thanks for your patience

 

[^woody^]

You just need to run your new DPC up or down the wall where the new extenion meets the existing house, and then overlap it with the existing DPC by chopping into the joint.

 

[jeds]

Personally I would fit a timber floor where it abuts an existing timber floor. Don't forget to extend the timber floor vents though your concrete floor.