[GymBoi]

Hi
I've an overlap slated chicken coop, which was given to us. My question is that as the slats overlap there is a gap; do I leave this gap as added ventilation or should I seal them up?.
Many thanks

[New shoot]

Coops do need ventilation, so if it is a deliberate gap at the top or base of a panel, that may well be what it is meant for. 

However, there are some very badly made coops on the market, which fall apart quite quickly and start having gappy walls.  These are not good for the birds as they are then sleeping in cold drafts, which can affect their health.

Hard to say without seeing the coop, but your post seems to imply gaps plural between each overlapping slat    If that is the case, I would say the coop will need a full refurbishment before use.  Maybe you could put some pictures on so we can advise you better 

[Sassy]

Agree with New Shoot. Ventilation definitely, draughts most definitelynot

[joyfull]

and if the gaps are really tiny they could be a hiding place for red mites