Healthy Indoors Magazine - USA Edition

Healthy Indoors | 29 and colder exterior are not usually great enough to create ventilating airflows. In my opinion, gable-end vents are the most effective way to go. One owner called me because his moldy attic had been remediated, and the mold growth was beginning to reappear, even though at the remediation company's ad- vice he had installed soffit and ridge vents. He had also closed off the gable-end vents, because he'd been told that "those are defeating the soffit and ridge vents." I was at the property on a hot summer day, and the attic was sweltering. I asked him to remove the poly covering the two gable-end vents, and within minutes, the attic was more comfortable. In New England where I live, mold doesn't grow in an at- tic in the summer, because any moisture that flows up into the attic from the house does not condense. In the winter and on cool, clear spring and fall nights, however, the mois- ture will condense on the cool sheathing, leading to mold growth. And it's not just humidification that adds moisture to house air. Building occupants produce moisture in a myriad of ways. We exhale water vapor when we breathe. We sweat. We hang wet clothes to dry indoors. We take showers. We boil water on the stove. All this moisture will rise up into the attic if there are pathways for airflow. Seal those pathways, and you will minimize the chances of attic mold growth, no matter what kind of attic ventilation is present. Stains around nails are not mold growth but are due to the chemical reaction between wet iron and tannins in the wood. May Indoor Air Investigations LLC Recommend that bathroom fans and the cook-stove fan exhaust to the exterior. An attic hatch or pull-down stairs should be as airtight as possible and be covered with a tightly-fitting insulated box. A door leading to attic stairs should be insulated at the attic side and have gaskets and some windows replaced, the installer had looked into the attic and found mold on the plywood sheathing. I could see visible mold growth on all the roof sheathing and gable-end sheathing, as well as smaller amounts of mold on the raf- ters. There were also puddles of black water on top of the vapor barrier and droplets of condensed water on the bot- tom side of the vapor barrier. Both bathrooms on the second floor of the home were venting into the soffit, which was covered with perforated vinyl at the exterior. The owner had scheduled a remediation company to deal with the attic-mold problem, but I told him that since his roof was over 14 years old, it might make better financial sense to replace the roof and sheathing altogether. Which- ever path he chose, until the mold was eradicated, I recom- mended that he stop using the all-house fan, which pressur- ized the attic, blowing moldy dust back down into the house. The bathroom exhausts also had to vent to the exterior and not into the attic or soffit. And meanwhile, he had to stop his teenage daughters from taking such long, hot showers! Right about now you may be asking "What about attic ventilation?" Soffit and ridge vents aren't altogether that ef- fective. In one house in which a bathroom fan exhausted into the soffit, there was passive air flow into the attic via the fan. I asked the owner to stand below the fan with a smoke pencil and add smoke to the air. I stood in the attic and watched as the smoke entered the soffit. Some of the smoke rose up in a laminar sheet along the sheathing (heated by the sun), and flowed under the ridge vent and over the ridge pole to the other side of the attic. The rest of the roiling cloud of smoke moved slowly up between the rafters, crashed into the ridge beam and then sank to the floor. I could not even tell if any smoke went out through the ridge vent. There was visible mold growth on the attic sheathing — heaviest near the soffit into which the exhaust hose was inserted. I can't tell you how many properties I've seen in which the installers had never cut holes for the ridge vent. Even if prop- erly installed, many ridge vents aren't adequate. Charles Headrick, an engineer with Headrick Building Products, built a rooftop/attic simulation device to test various ridge vents. He made temperature measurements in his experimental attic while heating the shingles with lamps to simulate the sun. He compared the temperature increases to a two-inch fully-open slot, to the temperature increases to a two-inch slot completely blocked with duct tape. Some roll-type ridge vents did not perform much better than duct tape! Air flows from higher pressure to lower pressure. Even with both properly installed soffit vents and ridge vents, the pressure differences in the winter (excluding wind influenc- es) due to air temperature differences between the cold attic

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