Firstly thanks for reading! I plan to lay Ployflor LVT interlocking herringbone (already bought). I am going to level the entire floor with 6mm flooring grade ply, and then self level over any dips etc, however I have a slight issue. Part of my kitchen is an old extension and is a concrete base, set roughly 7mm higher from just the area around it (but not rest of floor). My plan was to screw (or nail) the plywood over the rest of the house, and then glue the plywood onto the concrete area? Then I was going to self level. However I’m not sure which glue would be best to use. I’m worried if I was to screw the plywood into the concrete I may perforate any damp proof course as it doesn’t look that deep down. If I should still screw which would be the best shorter ones for the job? 2- slight side note question but I’m also not sure whether I should butt the plywood together, or leave gaps inbetween the sheets. I’ve seen recommendations for both? (I’m aware to leave a space around the edge of the room). Once again thank you, any help or advice is much appreciated