A central aim of energy-efficient building is to eliminate air leaks through the roof and exterior walls. A leaky building envelope not only makes it harder to heat and cool a house but also increases the risk of condensation and moisture damage.
Builders are getting the message about air sealing. But the tighter the house, the greater the need for some type of mechanical ventilation — and that raises construction costs. Is it possible to build a house with just enough air leakage to satisfy fresh air requirements without a ventilation system while still reaping some energy rewards?
This is basically the question Karen Leu grapples with in a recent post — and the subject of this week’s Q&A Spotlight.
Leu works for an Arkansas-based energy-retrofit program that aids mainly low-income families. She wonders what’s the best use of a limited budget: building to ASHRAE’s Minimum Building Airflow Standard and skipping the ventilation, or aiming for more rigorous air sealing and accepting the extra expense of ventilation?
What’s tight enough?
One camp argues there are no exceptions to the mechanical ventilation rule. “All new homes should have a mechanical ventilation system — even those that are trying to include ‘just enough air leakage’ to supply fresh air accidentally, through the effects of wind and the stack effect,” says GBA senior editor Martin Holladay. “Depending on random air leaks to supply fresh air is nuts.”
Inadvertent air leaks are greater on windy days, or in winter when the stack effect is strongest. But, Holladay adds, what about windless days in spring and summer? It’s not enough to hope that homeowners will crack their windows at the right time.
Holladay, of course, isn’t alone here. But under the circumstances — a retrofit rather than new…