Building Extension to DPC with existing house

[Steve111222]

Hi for my extension build I wanted to check what point I needed to build the engineering brickwork up to for DPC

The back of the current house has DPC below the Internal Floor level - I think is because it is a timber floor with space for vent. For my new extension, I was going to brick up to existing floor level and put the DPC there - would this be correct?

Existing House:

Should the DPC for the new extension be at the same height as the Existing DPC? or at the same height as the Internal Floor Level?

I have thought it needs to be at the Existing Internal Floor level as such:

 

[Notch7]

The 150mm MOT1 needs sand blinding on top.

Then lay DPM sheet. it needs turning up where it meets house so it high enough to come above the screed and can then be cut off flush.

Do you need engineering bricks? -usually 7n concrete blocks are used below DPC with a course or so of engineerings only needed to get you dpc height.

You need to extend the floor vents using 110mm pipe and join them to telescopic vents that go though the new extension wall. They dont have to be in the same place as a hole in the existing wall can be punched through to the void anywhere.

 

[Steve111222]

The 150mm MOT1 needs sand blinding on top.

Then lay DPM sheet. it needs turning up where it meets house so it high enough to come above the screed and can then be cut off flush.

Do you need engineering bricks? -usually 7n concrete blocks are used below DPC with a course or so of engineerings only needed to get you dpc height.

You need to extend the floor vents using 110mm pipe and join them to telescopic vents that go though the new extension wall. They dont have to be in the same place as a hole in the existing wall can be punched through to the void anywhere.

Thanks! No doesn't need to be engineering bricks was thinking to put couple rows of 7n Conc Blocks and then Eng Brick on top so will probably do that.



So will be something like this then?




I was going to put a 100mm DPC roll on the block / brick work at the DPC level in the new extension with something like this:




The a sheet on the floor (coloured in yellow in my drawing) does that then also need to go on top of that dpc roll in the new bricks?

 

[Steve111222]

Thanks! No doesn't need to be engineering bricks was thinking to put couple rows of 7n Conc Blocks and then Eng Brick on top so will probably do that.



So will be something like this then?

View attachment 147211


I was going to put a 100mm DPC roll on the block / brick work at the DPC level in the new extension with something like this:

View attachment 147212


The a sheet on the floor (coloured in yellow in my drawing) does that then also need to go on top of that dpc roll in the new bricks?

View attachment 147213

Would this be correct then?

 

[Notch7]

Looks about right to me.

Hopefully one of pro builders will be along to confirm.

I think I use 300mu gauge DPM -although I doubt it makes any difference.

 

[garyo]

Would this be correct then?

Looks good to me other than I'd also lap your orange dpm under the black dpc. This can be easier said than done depending on the mortar and how old and crumbly the existing dpc is.

 

[Steve111222]

Cool - thanks all.

 

[Steve111222]

The 150mm MOT1 needs sand blinding on top.

Then lay DPM sheet. it needs turning up where it meets house so it high enough to come above the screed and can then be cut off flush.

Do you need engineering bricks? -usually 7n concrete blocks are used below DPC with a course or so of engineerings only needed to get you dpc height.

You need to extend the floor vents using 110mm pipe and join them to telescopic vents that go though the new extension wall. They dont have to be in the same place as a hole in the existing wall can be punched through to the void anywhere.

Do the new airbricks in the new extension need to be below or above the DPC Layer? or does it not matter?