Ok I will most likely go with ditra, I was hoping I could tile directly over the 1" plywood to keep costs down the contractor also keeps assuring me that it is solid. Any issues down the road and I will be the one to call tough, so for future reference there must be 2 layers of plywood even over ship lap, I may also look into some other membranes that are more cost effective maybe a peel and stick membrane such as easymatt or mapegard