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Planning and Energy Bill

My hon. Friend is making interesting points about the value of insulation in this whole strategy. I note that the third line of new clause 1 refers to"““reasonable requirements for insulation standards””." Has he considered what is reasonable in respect of cost-effective insulation? A couple of years ago, we used to put in 4 in of insulation; now we put in 6 in—if not 8 or 10 in. However, there is a law of diminishing returns on the amount of thermal retention gained by increasing the number of inches of insulation that we put into lofts, for example. Has my hon. Friend considered how far it is reasonable to go, before we stop getting anything reasonable in return for our investment?