Natural Roof Ventilation Design

Each room should have two separate supply and exhaust openings.

Natural roof ventilation design.

Attic ventilation works on the principle that heated air naturally rises primarily utilizing two types of vents. Natural ventilation is based on two different principles which are cross and stack ventilation. It was shown in the bedrooms living spaces and mezzanine that openable roof windows help maintain low co2 levels. There was a general tendency towards better indoor air quality indicated by lower co2 levels in summer using natural ventilation than in winter using mechanical ventilation.

It is defined as using passive strategies to supply outdoor air to a building s interior for ventilation and cooling without using mechanical systems. For both attics and cathedral ceilings roof ventilation works best when it is balanced between high and low to take advantage of natural convection figure 2 55 at left. In short an adequate and balanced ventilation system is one that allows an equal amount of air to enter and exit the attic area. The maximum width that one could expect to ventilate naturally is estimated at 45 ft.

Natural ventilation has become a key component of green building today and is required in order to be certified by leed and the living building challenge lbc. Section 1203 of the nyc building code allows property owners to deploy natural and mechanical ventilation independently or simultaneously. Intake vents located at the lowest part of the roof under the eaves allow cool. This configuration also tends to evenly wash the entire underside of the roof surface with ventilation air.

However the code clearly states that natural ventilation is mandatory for any indoor location classified as habitable space by the nyc building code. Cross ventilation is the common way to obtain natural air supply in the buildings. Natural ventilation design contributes to energy efficiency in residential spaces while ensuring a supply of fresh air even without a mechanical ventilation system. Consequently buildings that rely on natural ventilation often have an articulated floor plan.

For all roof designs however the most important feature of a roof ventilation system is adequate and balanced airflow. As introduced in chapter 3 natural ventilation is a design strategy that can both reduce energy consumption and provide occupants with a positive psycho physical connection between inside and out. It is difficult to distribute fresh air to all portions of a very wide building using natural ventilation.