The instructions are to be used a guide. I researched this shower and spoke to the support gentlemen Robert who was very knowledgeable and helpful. the shower is very good quality however is difficult to out together. You need to make sure the base is level and square otherwise everything else will be out. You will need to build up behind the walls a frame on the drywall or cement board to provide support. Also you will need to caulk and silicone are cranks and gaps. - good tub adhesive will be you best friend.