I've previously noted how the Cincinnati area is full of homes where the upper level gets significantly warmer than the main level, prompting homeowners to jack up the AC more than necessary. The main culprits is that many homes have 1) insufficient ventilation to clear hot air from the attic, and 2) lack enough insulation to keep the conditioned air from escaping into the attic.
In the most recent encounter with a ventilation problem, the insufficient ventilation was compounded by bathroom fans venting into the attic rather than out of the house. This combination likely created an ideal climate for mold to begin growing on the roof sheathing. Not only does this create a potential health hazard, the normal lifetime of the roof can be compromised. So, in this case, not only does the homeowner have to spend a significant amount for cleaning up the mold situation, but was potentially causing a shortened roof life along with additional expense to heat and cool their home.
This situation is not as unusual as you might think and is not limited to multiple story homes. There are plenty of ranch houses that lack sufficient airflow as well. In many homes, the only ventilation are one or two passive vents or a ridge vent on the rooftop that are supposed to work in tandem with air coming from soffit or gable vents. Unfortunately, the soffit or gable vents have often been covered up (e.g,. when siding was added or boarded up to keep animals out).
If this sounds like a situation that could exist in your home, here's some suggestions:
- Ideally, have a roofing or other building professional check the airflow in your attic to determine if it is sufficient for the home and identify corrective actions.
- Check that vents have not been inadvertently covered by siding or other items.
- Add attic fans to help draw hot air out if appropriate. I'm personally fond of solar fans which can be installed without the need to run electric wiring to the attic and don't have any operational expense.
- Ensure proper attic insulation and air sealing between the attic and living space. This is critical when using powered ventilation that could pull conditioned air out of the house.