Conservatory base

Hi, I'm looking to build a 5m x 3m timber framed conservatory with a Tapco plastic tiled roof. For the base I was going to use 6x2 tanalised timbers on joist hangers coming from the external house wall and fixed to a timber beam using joist hangers sat on concrete pads just like the steel base conservatory system. The ground is very firm but the problem I have is I only have 3 inch of void underneath the joists. The joist ends are going to be wrapped and my thoughts are to lay a membrane under the joists to prevent any chance of moisture penetration. Any thoughts?

 

Hi, Darren. Yes I am going to use 6x2 timbers for the base. But my only worry was being so close to the ground. You normally need a minimum of 12" void under a timber floor so thats why I was wandering if using a membrane directly under them would be suffice.