We realised you weren`t a trained chippie when you said depth, but we had to clarify the height/width thing before giving advice. Bandymandy then comes on with the moronic statement, it doesn`t matter. This guy has a bee in his bonnet about ANY tradesman, he seems to think that using correct terminology, tried and trusted methods is for the birds. I think in his "mind" he is using intellectual argument to shoot down professional people. In this instance your post was answered before he came on with his bullpoo. As you can see, he still will not let it sink in, the guy is a fool.