No DPM until walls errected?

[omph]

Is it normal to build an extension and leave the flooring till last ? I've seen this on a number of occasions. How would they ensure and prevent rising damp if the DPM is not installed correctly ? From what I understand, the DPM should be sandwiched into the inner leaf brickwork (image attached), but it is impossible if you've already built the walls.

I can however see the convenience of it though i.e. not having to worry about damaging the DPM.

 

[jono_h]

The DPM ‘sandwich’ is a common detail, but there are other solutions. You could install a wider damp proof course, which sticks out internally and is then folded down & sealed against the DPM when it gets installed. That would maintain the protection, but reduce the risk of damaging the DPM before it is protected by screed / insulation,

 

[omph]

The DPM ‘sandwich’ is a common detail, but there are other solutions. You could install a wider damp proof course, which sticks out internally and is then folded down & sealed against the DPM when it gets installed. That would maintain the protection, but reduce the risk of damaging the DPM before it is protected by screed / insulation,

Isn't that risky though ? What if the tape comes off ? or doesn't fully seal ?

 

[noseall]

Isn't that risky though ? What if the tape comes off ? or doesn't fully seal ?

A small risk. You could damage the DPM or DPC (depending which you leave sticking out) whilst building, but it could be repaired. DPM's are often joined and taped, no dramas. When ever we do a B&B floor, we leave the DPC trailing out, so that we can visqueen, insulate and screed, later on.

 

[^woody^]

Isn't that risky though ? What if the tape comes off ? or doesn't fully seal ?

It's not sellotape. A proprietary butyl or similar tape is used, along with double folding the lapped membrane.

 

[omph]

So much of the DPC should be protruding out ? 100mm ? 200mm ?

 

[noseall]

So much of the DPC should be protruding out ? 100mm ? 200mm ?

We leave enough to be useful. 300mm+