Builders are adding an extension to the bungalow. The new extension has a cold roof as height is a limitation for other reasons. The roof joins the sloping tiles of the main sloping roof, about 9" higher than the old guttering. I'm not confident that their claim that ventilation is all dealt with is correct. There are vents at the lowest end of the flat roof i.e. in the soffit, but how is ventilation achieved at the other end? I think they mentioned ventilating into the main roof space but that sounds sketchy. How would it normally be done? What complies with regs?