Warm Roof Air Gap

An unvented roof assembly is possible only if you keep the roof sheathing warm enough to prevent conditioned air from condensing against it.

Warm roof air gap.

A cold roof can be cheaper as ridged warm roof insulation tends to be more expensive a warm roof is sometimes the only option when it is difficult to get the required cross ventilation rigid warm roof insulation can allow for smaller timber depths as the 50mm air gap does not have to be maintained. If i had to choose between a 1 2 inch gap and a 1 inch gap i would be inclined to go with the 1 inch gap if i were building in climate zone 5 or anywhere colder. The r value achieved by an air gap is dependent on the emittance of the surfaces on either side of the gap. Insulating along the sloping rafters forms a warm roof and is an option for both new builds and refurbishment projects.

The warm side of the insulation i e. The roof should also have ventilation openings of at least equal to a 25mm continuous gap running the full length of the eaves on two opposite sides. Between the insulation and the ceiling finish. There are two types of flat roof systems warm and cold roofs which affect the positioning of the ventilation.

Heat flow through air gaps associated with floors ceilings or roof elements will have r values that are greater downwards than upwards. Therefore this element alone can account for as much as 25 of a buildings heat loss. Taking advantage of this natural process referred to as passive ventilation is the most common way to vent an attic. Hot air exhaust vents located at the peak of the roof allow hot air to escape.

Flat roof ventilation allows for the circulation of air in the property particularly for warmer rooms in residential buildings. Unvented roof assemblies should be insulated either with air impermeable insulation rigid foam or spray polyurethane foam or with a combination of foam and air permeable insulation. When thermal insulation is placed below the deck the ventilation must also be on the underside. If you don t want to use sips or nailbase read this article tolearn the four basic approaches to insulating unvented roof assemblies.

Generally vertical air gaps in walls have the same heat flow inwards and outwards. 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.