Beam and block floor joining existing house below DPC

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Hello, hopefully one of you kind gents can help me out..

Having an extension that raps round my semi detached house in a L shape. I'm trying to manage the build myself and trying to get my head around the ground floor.

Suspended floor is forced upon me thanks to deep foundations. So I want to use beam and block...

The beams have to run from the outside wall to the existing house because the beams would have to be 8m plus running from front to back if you get me.

Because of the floor level in relation to current DPC (floor is 160mm above DPC), the beams will have to sit 150mm odd below DPC so that the insulation and screed can be level with existing floor.

I understand that I can have a split level DPC in the new inner cavity wall and that it can lap up to meet existing DPC.

To meet house I will be making 150mm holes in the existing house to put one end of the beams in, with the the other end sitting on the dpm of the inner leaf of outside wall. This will surely mean the beams and blocks will get damp? Because the holes are below doc. Is this ok? I know I can put DPM on top of the floor to prevent damp bridging up the walls, but I'm not sure if this is the correct way to join onto house?

The holes I'll be making will be just below the house DPC, do I just need to be extra careful not to damage the DPC when making the holes?

Also if one end of the beam gets damp, is there any point in there being a dpc below the beams at all? Is it ok to rely on just the Dpm above lapped into house dpc?

Thanks
 
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After a lot of thinking... Could I tank both the beam ends and holes in wall and then also wrap the end of the beam in a a damp proof membrane.

What would building control make of that??
 

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