In a 'cold' pitched roof, the insulation is fitted at ceiling level. With this construction, there is a risk of condensation on the underside of the roof; the thicker the insulation layer, the greater is the risk of condensation and of damage to the materials. Since the late 1960s, the accepted solution has been to introduce ventilation into the loft space by openings to the outside at eaves and ridge. More recently, vapour permeable underlays are sometimes used as an alternative to ventilation. With the introduction of the unventilated cold pitched roof, we need to clarify the general principles and risks and identify approved construction techniques. By giving guidance on the technical risks associated with ventilated and unventilated forms of cold pitched roofs, this Good Building Guide responds to some of the confusion and conflicting views. 6 pages.