Warm Roof No Ventilation

Without adequate ventilation moisture rises with the hot air and forms condensation on the inside of the roof deck.

Warm roof no ventilation.

The map at right which is based on table r806 4 of the irc lists the minimum r values required to prevent condensation in unvented assemblies in various climate zones. 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 roof assembly has enough insulation and it is properly installed. No ventilation is required for these types of roofs.

Venting prolongs the life of the roof. The building envelope is tight enough to prevent warm moist air from escaping from the building interior into the roof assembly. Warm roof ventilation specification for a simple duo pitch roof bs 5250 specifies sufficient ventilation as being. Openings along the sides allow air out of the attic cooling the space and lowering your air conditioning bill.

The article notes that the ventilation cannot overcome the significant humidity drive into the flat roof structure caused by small air leaks. Roofers use a circular saw to cut a long slot along the roof ridge if there isn t one then cover it with a plastic flap as shown or a flexible vinyl matrix. An unvented roof assembly is possible only if you keep the roof sheathing warm enough to prevent conditioned air from condensing against it. If ridge or eaves ventilation is not possible ventilation tiles can be used at high or low level to achieve the required airflow.

Worse yet inadequate insulation is almost surely allowing moisture laden air into your attic. This moisture is released into the air inside the house from bathing cooking plants laundry and other causes. When the condensation forms on the roof deck it begins to rot the wood. 25mm at eaves on each slope and 5mm at ridge.

Unless your roofing system has insulation on the roofing deck and is designed without ventilation your furnace should not be heating your attic. There is enough exit ventilation space to match the amount of soffit ventilation inlet.