I have received a few quotes to replace my roof tiles. One company have stated they strip back the roof completely removing the celotex insulation boards and then deck with sterling board and then a breathable membrane. Another company states they dont remove the celotex insulation, they deck over this. I am confused. Both companies quoting similar prices. Are there any roofing experts out there who can advise the correct procedure in retiling a roof. My house is a 1950's style bungalow. Thanks