Raised Conservatory Floor Base

[QuestionsQuestions]

Hello

I would appreciate some advice.
We are having a conservatory basework done and the floor needs to be 300mm above ground level to be in line with the back door.
The builders have built the requisite dwarf walls taking into account the raised floor. They are now building the floor and have attached a wooden frame to the brickwork and the back of the house that is level with the back door. They have put 100mm polystyrene block in between the joists and there is a gap under this which is just earth. Is this sufficient to insulate a floor so our sun room can be used all year round. we intend to tile and use underfloor heating. I am a building novice but will the wooden joists rot as they will (might?) be subject to moisture from the earth underneath as the temp drops and increases (i don't know about this)
Any advice will be gratefully received..What i dont want is a room that loses lots of heat through the floor ..or a floor where the joists have rotted in 10 years and need replacing.
With Thanks

 

[freddiemercurystwin]

A conservatory will never be suitable for all year use, it'll be cold in the depths of winter and boiling at the height of the summer.