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The importance of good ventilation

In previous columns, I have mentioned the term "building science," an approach to building or remodeling a home that takes the laws of physics into consideration. In the "old days" builders had practical experience and rules of thumb passed down from generation to generation that helped guide the building design and construction techniques they used. For example, they knew what standard-size lumber to use depending on the span and load, and that a rot-resistant wood (like redwood) made a better siding product than a wood species without natural protection. (As a side note, there are numerous modern day, green alternatives to wood siding of any species — perhaps a topic for a future column!)

Builders of yore knew that without adequate ventilation, a basement was likely to be musty and damp. Likewise, a few screened vents in the roof eaves and some kind of attic vent would help keep the house cooler in the summer. When deliberate energy conservation measures began to be incorporated into homes to make them "tighter" and more efficient, a more holistic and scientific approach to building became necessary and building science was born.

One might think of a home as a "living structure," because it is occupied by living things. Those living things breathe, take showers, heat water and food and do other activities that create warm, moist air inside the home. When that warm, moist air finds its way to cooler spaces, it condenses on the surfaces, similar to the way a glass of iced tea "sweats" on a countertop. If condensation is allowed to accumulate in enclosed spaces, bad things happen. Wood rots, and insulation becomes saturated with moisture, rendering it ineffective.

Good ventilation in the living space of the home and in the attic helps keep the moist air moving, ultimately replacing it with dryer air, so that condensation and its eventual damage is minimized.

There is an incredible amount of data available showing the measureable improvements in temperature control and energy conservation achievable with proper attic ventilation. One of our roofers and ventilation specialists, Fred Worrell of Worrell Roofing, has plenty of real-life success stories to tell. On a project in Palo Alto, after installing roof ventilation and a radiant barrier, our client noticed that the house temperature was more comfortable, and during a recent heat spell, the air conditioning was not needed during that time.

Then there is the not-so-happy-ending stories on other projects. A previous roofer had omitted adequate roof ventilation and the 15-year-old roof had to be replaced, along with a large amount of roof framing, because of dry rot from condensation.

Modern homes are much "tighter" than older homes. In the past, the small unsealed gaps in windows, doors, interior and exterior trim and other joints in materials, along with the lack of insulation, provided a means of air movement and ventilation. With the push for energy conservation, sealing and insulating the building envelope became essential. These new measures kept the warm or cool air in, but also kept moisture and indoor pollutants in as well. Reports of "sick home syndrome" and increased allergies or illness soon followed.

Building science once again can be used to address inadequate ventilation in the home. The main idea is that slightly positive air pressure in the home (compared to outdoors) can help push stale air out, while bringing in fresh or filtered air to replace it.

This can be accomplished in a few different ways, but one of our HVAC specialists, Bill Shepherd of Shepherd Plumbing Heating and Air Conditioning, has impressive stories about dramatic improvements in clients' quality of life because of proper ventilation.

He tells of one family who suffered from allergies and mold sensitivities because of damp soil conditions in their home's crawl space. The dampness migrated up through the floor and into the home. In addition to foundation and drainage repairs to help dry the space, Shepherd installed a dehumidifier and a heat recovery ventilator, a device that brings in fresh air and transfers the heat or coolness of the stale air to the fresh air as the stale air is exhausted. This produced the necessary positive air pressure in the home, bringing in fresh air while pushing out pollutants, and avoided wasting the energy they had already paid for to heat or cool the home. The family noticed immediate improvements in their health.

Building science has created many other improvements in people's lives. As our study and application of building science expands, we can expect to see those improvements find their way into all of our buildings, new and old.


Ciro Giammona is CEO of Harrell Remodeling Inc., Mountain View. He can be emailed at cgiammona@harrell-remodeling.com.

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