I am planning to put a raised floor at the back of my garage (2.4m x 2.4m) to create a utility area. I have spoken with the local planning dept and I understand that when I eventually separate this area from the garage with a stud wall I will need to go through development control. But for now, I'm just putting in a suspended floor.
The question is, how do I best insulate the floor (so that I won't have to take it up when I do the full conversion).
Building Control have agreed that I can lay 4x2 beams on the exisiting concrete floor (which I have assumed already has a DPM) and use T&G chipboard sheets. For insulation, they have simply told me to meet the necessary U values (which I had to look up for myself!) and will not give me specific advice on this.
My plan was to use polystyrene sheets, but I have read that these are more suitable for under concrete floors due to the fire risk and that I need to consider air flow and the risk of water leaking from the washing machine as well.
Can anyone please help:
1. what's the most cost effective insulation for this and what thickness should I use to meet BC requirements - eg the polystyrene is 50mm thick, but can't get any info on what U value this gives me - would it be safer to put down 2 sheets?
2. Do I need to allow for airflow under the insulation and if so, is it acceptable for me to create some air holes/grooves in the beams to achieve this?
3. Should I take any further precautions as this is a 'wet' area?