Natural ventilation is one of the most energy efficient, natural ways to maintain healthy indoor air quality in a home.
Natural ventilation dilutes and displaces indoor air pollutants, and enhances thermal comfort, by relying on planned openings and scientific principles like buoyancy to move air around the building envelope.
Air flow through the attic space is key to natural ventilation. The general rule of thumb to achieve adequate air flow is 50% intake under the eaves and 50% exhaust near the peak of the roof. Ideally, the system should allow greater intake than exhaust.
Many historic homes still exhibit classic signs of natural ventilation – wide eave overhangs, narrow rooms, and a roof ridge perpendicular to the prevailing winds. At the same time, many homes that are currently being built fail to meet minimum building standards for natural ventilation. Homes that fail the natural ventilation test often result from one of these modern issues:
Complicated roof lines
Roof lines have become more complicated on modern homes, resulting in the need for careful calculation of intake and exhaust.
Technical improvements have been made in exhaust technology, but corresponding improvements in intake technology lag behind. Most full vent soffit products do not allow sufficient intake (expressed as “net free area” or NFA) to work with the better modern exhaust products and provide the balanced amount of roof ventilation that is required for most homes.
Typical vinyl soffit with inadequate airflow.
Due to modern design standards with smaller overhangs, it can be difficult with most soffit products to achieve sufficient intake for the exhaust at the ridge vent.
Modern homes often have overhangs that are less than 1′ wide.
Inadequate center vent soffit
For aesthetic reasons, center vent soffit is often selected to handle intake. Many center vent soffit products decrease intake, so intake becomes insufficient to balance exhaust.
It’s challenging to get enough airflow when using only center vented soffit.
Complicated building codes
In many cases, builders do not necessarily follow the minimum building codes through lack of understanding or awareness of proper ventilation, and inspectors may not verify compliance with the codes.