Try this calculator from Knauf Marmorit to get an idea of your U value. Include every layer of your wall including the internal plaster and see what total you have. You can also download the generic U value table from our brochure download page to give you a guideline of the sort of U Values you can achive or use the links at the bottom of our welcome page for in depth explainations of the U value and your possible wall construction. Please feel free to call us if you require any assistance.