Window detail with no cavity closer

[Super_Paulie]

Hi guys. 

After some quick advice on one of my windows. I'm about to board the reveals, but the lower cill has no cavity closer like my other windows but it does have a DPM as a cavity tray going into the outside leaf.

 

How am I meant to detail this, merely drop an insulated board over the top of the DPM? I can see outside brick under the frame of the window so not sure the best way to proceed.

 

Cheers guys

[Super_Paulie]

for info i foamed in some PIR, levelled the sill with ply and looped the DPM over onto the ply and stapled it down, ready for a window board. Rightly or wrongly!