Cold Flat Roof Ventilation Detail

Flat roof ventilation allows for the circulation of air in the property particularly for warmer rooms in residential buildings.

Cold flat roof ventilation detail.

2011 code of practice for control of condensation in buildings stipulates that there should be a ventilation gap between the insulation and the bottom of the flat roof deck of at least 50mm. Cold roofs and warm roofs. Basically the term cold roof refers to a traditional roof or vented roof while hot roof refers to a roof that is not ventilated and which has foam insulation attached directly to the roof sheathing. Their layer of insulation is beneath the roof decking and the roofing membranes.

A warm deck roof is where the insulation is placed on top of the rafters joists and the roof covering is then placed over the insulation. The wider the span the more free airflow is required in the roof space. That means the rest of the roof is protected from heat. Cold roofs have the waterproof layer placed directly onto the roof deck and the insulation inside the roof just above the ceiling.

There are two types of flat roof. A cold roof really is colder than the rest of your home in the winter which means condensation is much less likely to develop. When thermal insulation is placed below the deck the ventilation must also be on the underside. In this case ventilation is required and the roof can still become wet with condensation which may cause materials to decay.

This video shows the key features of a flat roof cold deck construction and how to draw the details to a scale of 1 10. No ventilation is required for these types of roofs. A cold roof system sees the insulation placed immediately above the ceiling between the joists with ventilation space above the insulation. The minimum requirements for cold roof ventilation are set out in bs 5250 control of condensation in buildings which takes into consideration span pitch and roof area.

Why don t cold roofs need to be ventilated. In a concrete deck for example this gap could be created by fixing 50x50mm timber battens at 600mm centres and attaching the insulation to underside of these battens. There are two types of flat roof systems warm and cold roofs which affect the positioning of the ventilation.