Hi!
My current project is to have an enclosed front porch - that is an add-on to the front of the house approximately 2 metres by 1 metre. It will have double glazed windows and insulated roof. I had intended to have cavity wall with a 2 inch/ 5 cm gap for insulation.

A surveyor acquaintance says that the firm he works for fits double brick without a gap so as to allow an extra 2 inches internally per wall.

This all sounds very well, but won't that defeat the object of having energy efficient / double glazing? Or should I be cutting my costs and having single glazing too? Any comments would be welcome.

Thanks