laying a DPM for a new slab, corner details

[browfish]

I am about to lay the hardcore and sand blinding for our extension followed by the DMP before the slab. Questions are
1) should the sheet DPM be laid over the wall DPC or under it? and shoudl it overlap the whole width of the inner wall?
2) internal corners are fine as i can obviously pleat surplus material to fit neatly however, i have a couple of external corners too. What is the detail here. I obviously cant cut the DPM to fold around the corner as this would breach the DPM. Any ideas?

 

[noseall]

The dpm is laid prior to the dpc so it goes under.

Allow plenty of lap initially because the concrete will pull at the polythene. When it comes time to lay the dpc, we usually trim the dpm so that it laps onto the brick by 50mm or so. It can cover the whole width of the brick if you like but it must not go into the cavity.

Cut a separate strip of dpm to lap around the corners behind the main sheet then slit the main sheet to suit. Crikey that last bit of the sentence is hard to say quickly!

 

[tony1851]

I am about to lay the hardcore and sand blinding for our extension followed by the DMP before the slab.

Just a small point; nothing to do directly with the dpm but are you putting insulation in/on the floor? Usually it's laid between the dpm and slab - though you might just have forgotten to mention it?

 

[noseall]

Just a small point; nothing to do directly with the dpm but are you putting insulation in/on the floor? Usually it's laid between the dpm and slab - though you might just have forgotten to mention it?

Unless underfloor heating is being installed, then it is preferable to install the inso' directly below the screed.

 

[browfish]

Yes, I am Installing insulation. Yet undecided wether to install it beneath the slab to provide a heat sink for the underfloor heating or above the slab for a quicker response time. Can't make my mind up.
Thanks