Ventilate Right: Ventilation Guide for New and Existing California Homes

Why Ventilate?

The Case for Installing Well-Designed Ventilation in ALL Projects

A good mechanical ventilation system can help protect buildings and their occupants. Inadequate ventilation often leads to increased levels of moisture and pollutants in a home. It is not feasible to constantly assess indoor air to determine when pollutants are at unhealthy levels. The best protection is providing background ventilation to constantly remove indoor air and replace it with fresher outdoor air, and to provide extra ventilation equipment where pollutants and moisture are commonly produced (the kitchen stove, bathrooms, laundry rooms, hobby areas). Even if adding mechanical ventilation is not required by code, consider meeting ASHRAE Standard 62.2 in all your additions, alterations, and energy upgrades to protect the health of your clients and to reduce the risk of moisture damage in buildings.

Build Tight, Ventilate Right

Heating and cooling make up the largest piece of the energy use pie chart in most homes. Since air leaks are estimated to account for a third to a half of space conditioning costs, making homes as tight as possible saves energy. The goal is making buildings tight and providing effective, well-designed ventilation systems to control the levels of indoor pollutants.

Making a house or apartment unit as tight as possible improves comfort by eliminating drafts. Limiting air movement through the building envelope also limits moisture migration, reducing the risks of moisture damage in attics and wall assemblies. When combined with effectively designed and operated ventilation, a tight home provides better control of air movement and reduces the chances of mold, wood decay, and harmful levels of indoor pollutants. Please see Why is Mechanical Ventilation Required?

Balancing Energy Efficiency with Indoor Air Quality
  • Tight building
  • Decreased energy use
  • Well-designed ventilation system, properly installed and operated
  • Acceptable indoor air quality
  • Decreased health risks
  • Reduced occupant complaints
  • Reduced moisture levels in structure

Build Tight: Guidelines for Existing Homes

So what are the best current recommendations about how to properly seal air leaks in homes and apartments? The U.S. Department of Energy brought together some of the most experienced professionals in residential energy efficiency upgrades to create a set of guidelines for all the steps involved in increasing the energy efficiency of houses and apartments. These Guidelines are intended to form a basis for consistent training, assessment, and completion of all aspects of residential energy upgrades across the United States. Section Four of the Workforce Guidelines for Home Energy Upgrades addresses air tightening and is a good primer for contractors on what to do (and what to avoid) when doing residential air sealing work.

Also, the Building Performance Institute (BPI) offers comprehensive standards and training related to residential energy upgrades. BPI certification is required for contractors who wish to participate in many rebate programs in California, and many BPI protocols have been adopted by California utilities.

For more information on BPI standards and training, go to the BPI website. For more information on utility rebate programs, go to Energy Upgrade California.

Avoid Repeating Past Mistakes

"Build tight, ventilate right" grew out of hard lessons in building science learned by contractors and homeowners. In the 1970s and 1980s, rising energy costs created a push to make homes more energy efficient. People insulated, caulked, weatherstripped, and replaced leaky windows and doors to reduce household energy costs. Heating and cooling bills went down, but a new set of problems emerged: moisture damage and poor indoor air quality.

  • In some weatherized homes, occupants complained about stuffy air and moisture-related problems like mold on drywall, dripping window frames, and premature failure of building materials.
  • In areas with cool winters, roof sheathing in some buildings began to deteriorate after attic insulation was added. Warm, moist household air moved into a now-colder attic through unintentional openings. Condensation formed on roofing nails and sheathing, encouraging the growth of mold and rot.
  • In air conditioning climates, some buildings developed problems with mold and drywall decay when too much exhaust ventilation was used in leaky buildings with vinyl wallpaper and other impermeable surfaces. Moist outdoor air condensed in the wall cavity on cold drywall surfaces, causing failure of the wall assembly.

It became clear to the building industry that saving energy in buildings was more complicated than increasing insulation R-values, installing new windows and doors, and sealing air leaks. Air movement and moisture levels had to be understood and controlled to protect the buildings and their occupants. Guidelines from the U.S. Department of Energy (DOE) and the Building Performance Institute (BPI) reflect current research on how to build a tight, well-insulated home without revisiting past problems.

Hard Lessons from Tighter Building in the 1970s
  • Energy costs
  • Air leakage
  • Moisture problems
  • Indoor pollutant levels
  • Health risks
  • Mold & rot
  • Occupant complaints