DPM under concrete floor in a doorway

[Paul200]

Hoping someone here can help with this one.

Recently moved into a 150 year old stone built cottage with concrete floors. Original walls and floors have no dpc or membrane that I'm aware of but recent extensions (20 years?) have concrete floors over a dpm. At the back door the concrete sill is simply an extension of the floor inside and the dpm exits to the outside about 200mm below floor level. I've excavated the area around the doorway to install a step and found there's about 300mm of dpm flapping around in the breeze - and presumably been channelling water back into the slab.

My question is what to do with the dpm? My first thought was to bring it back up the front of the slab, fold it over the top and somehow seal it to the top. And maybe install a timber threshold over it (currently there is an Exitex threshold channel thingy which mates with it's other half on the bottom of the door which actually works at keeping the weather out but leaves about 75mm of the slab exposed to the elements!).

Am I right in thinking that maybe this is not how a dpm is normally terminated at a doorway? And how should it be done?

I've searched high and low on the interweb for an answer and got precisely nowhere so I'm hoping that someone on here has experience of old properties and can point me in the right direction.

Cheers

Paul

 

[MMUK]

Under normal circumstances with a cavity wall system, the dpm for the internal slab laps up the internal brick course and is cut flush to the final slab height. This edge is then hidden once walls are plastered. Across a doorway it is the same with the cavity left open and capped with a threshold board.

I'm assuming the section you refer to is on the extension? The concrete outer cill should be completely separate from the internal pad. I would recommend cutting it back flush to the internal wall, lapping the membrane up and fit a piece of celotex then concrete a new step. You are in effect creating a filled cavity if you follow me?

 

[Paul200]

Yep - that makes perfect sense MMUK. The cavity wall scenario is all I could find on the internet and I did wonder if I should chop the threshold out and do something similar. Daft thing is, the front door is in the original part of the building and has a totally separate cast step - no membranes or anything - just a small gap. In fact the original building has no trace of damp whatsoever whereas this newer extension always smells musty. Think the old 'uns knew a thing or two!

Thank you - much appreciated

 

[Paul200]

It does make me laugh! I've been trying to find an answer to this problem for a while, off and on, and the answer comes via a woodworking forum. Top people, all of you