New dpm to new dpc and old dpc

[RedHerring2]

Sorry, I need your advice (or approval) again.
I'm not at that stage yet, just thinking ahead.
I'm going to be installing a new dpm and I have to, partially, match to an existing dpc. Plan attached, new walls in red:
View media item 27646
Bathroom will be completely new slab and kitchen will be partially new slab, i.e meeting and matching existing slab, with overlapped dpm below screed.

The issue is the exisiting dpc is about 175mm below internal ffl. As shown;
View media item 27647
Where the new dpm meets the continued dpc in the new walls, there's no problem I can just lap the dpm over the new dpc, even though it'll still be about 175mm below ffl 'cos I want to maintain the same ffl throughout. And it'll mean laying a couple of courses above dpc before laying concrete slab.
As shown:
View media item 27648
Where the new dpm meets the existing dpc in the existing walls, I was going to just extend the dpm up the wall to finish about level with the top of the screed.
The new dpm will be about 75mm below existing dpc, below insulation.
So it will be a bit of this and a bit of that.

Anyone see any problem with that?

 

[theoldun]

Quote
Issue is the existing dpc is about 175mm below internal ffl, as shown.

Technically, slab has not been laid in correct position in relation to existing DPC and there is a passageway for damp to bye pass the DPC . However as there is nothing that you can do about it and you have made no mention of damp, would suggest you put it out of your mind. You must have one ecking big step at external doors if floor level is 175 above DPC and path level is 150 below DPC.

Quote
And it'll mean laying a couple of courses above dpc before laying concrete slab.

There is no reason on cavity walling why you can not lay a split level DPC if the situation requires. Internal DPC can be above or below external in certain situations.

Regards your DPM to kitchen and bathroom where it will join into existing oversite, lay out plenty of visqueen, so that when you demolish side walls and back filled footings you have enough to go over and up side of existing slab. Run saw across and cut back 100mm existing screed cut poly level with concrete slab and apply two coats of Ikopro Synthaprufe in 300mm band over joint before laying screed.
oldun

 

[RedHerring2]

Thanks 'oldun. You're a star.
No current problem with damp.

......You must have one ecking big step at external doors if floor level is 175 above DPC and path level is 150 below DPC.

Well, actually, the external ground level is about 7 courses below dpc. What's that? About 500mm? So it is "one ecking big step".
Originally, I suspect the ffl was level with dpc but over time slab has been laid in kitchen and outside wc (which will become wc in new bathroom)without taking up original.
There was also a lobby between kitchen door and outside wc door that was original ffl. So there was a step down to that before the back door proper. Then a disabled ramp which was a bu99er to break up. (Which was completely stupid 'cos there was a 175mm step down from the kitchen to access the ramp )

..There is no reason on cavity walling why you can not lay a split level DPC if the situation requires. Internal DPC can be above or below external in certain situations.

'cos I'm matching/continuing existing dpc, is there any point in changing it?

Regards your DPM to kitchen and bathroom where it will join into existing oversite, lay out plenty of visqueen, so that when you demolish side walls and back filled footings you have enough to go over and up side of existing slab. Run saw across and cut back 100mm existing screed cut poly level with concrete slab and apply two coats of Ikopro Synthaprufe in 300mm band over joint before laying screed.

That's the kind of thing I was thinking, but thanks again for confirmation, name of liquid waterproofer and clear instruction.