myself and a friend went to the self build show in belfast at wend,we spoke to the main insulation companys present i myself am intersted in external insulation he is going to use cavity insulation,to exceed way beyong regs. kingspan said they have a 100mm cavity board but couldnt say what u value he'd get,it's not in brochure or web site,xtratherm say to use 80mm cavity board,insulated dry line to reach .015,when asked about dew point at party wall meet outer wall they say its insulated anyway by cavity insulation and any differnce wont affect it finally aerobord say to use their 140mm cavity board in a 150mm cavity to reach u value 0.019.is this the best method ,and is dry lining that bad when cavity is insulated.some pople say kingspan is best but as far as i can see aerobord wins for being the most straight forward ,any thoughts?