I am not a fan of the self adhesive tiles. You really have to have an excellent flat floor underneath to get them where the seams won't open up over time. But since you have the prerequisite floor to lay them on, it should be no problem. My suggestion is to start laying the new tile such that the seams don't line up with the seams on the existing. Lay the new ones so the center of each tile is centered on the cross formed by the juncture of 4 existing tiles. If the existing tile has a pronounced texture, it may over time show thru the new tile. Make sure the existing floor is scrubbed and dry. Luck, Kizmet