To follow up my most recent e-mail. I don't know what level of protection I want because I am nw quite out of my depth here. I'm just a householder wanting to make sure that I'm doing the right thing. You are clearly much more expert than me. What do you advise?
The level of fire protection would need to be sought from your local authority to ensure compliance but we would assume as you have advised that the ceiling has 'fire-retardant boarding' that any requirement for separation/compartmentalisation had been achieved by this (i.e. 30min, 60min, etc.).
So assuming it is just a surface spread of flame concern for the outer facing plywood then we would suggest the exterior grade spec. of the Thermoguard Timbercoat BS Class 1/0 & EN Class B System.