Membrane under concrete for conservatory question

[Doobrey]

Hi,

Just finishing off the base of a conservatory (my first home built !)

The unit is 4m by 4m.

I have membrane with is 4.2m by 25m in length.

Question is, when I lay the membrane down, I understand I need to bring it up the sides. Considering it will only come up the sides my 10cms on each side, is it worth cutting 2 pieces of membrane and overlapping them to that the sides can rise above the level of the concrete, to cut flush later?

Or should I simply use one piece of membrane and cut it exactly 4x4m square, but cannot come up the sides?

Thanks in advance,

Doobs

 

[noseall]

Use two pieces.

Ensure the pieces lap over each other by 600mm and tape them.

Lap the dpm onto the blockwork.