Venting a Tricky Old Roof
Retrofitting undershingle intake and ridge vents helped to cool and dry this 120-year-old attic.
Synopsis: While old houses can have enormous appeal, they also can have big problems, including air-circulation issues. In the course of various renovations to an old house in Rhode Island, FHB editorial adviser Mike Guertin upgraded the ventilation to bring the attic into the house’s building envelope. Because Guertin couldn’t install air-intake vents at the eaves, he had to use rooftop air-intake vents. He then installed ridge vents to balance the system and allow it to circulate properly. This article includes information about the way to calculate the proper amount of venting for any roof.
I’ve been working on this old house for a few years now. Among other projects, I retrofitted the house with central air conditioning, which has duct runs in the attic, and updated the bathroom, swapping the original claw-foot tub for a walkin shower. But I’m not the only remodelling contractor who has worked on this house since it was built in the 1880s. The roof has likely been replaced a few times, most recently with asphalt shingles and roofing underlayment. And at some point in the 1970s, the attic was insulated with loose fill.
As soon as I started working on the house, I knew that it might have attic-ventilation issues. After all, when the house was built, it wasn’t insulated and couldn’t have been as tight as it is today. Rather than strain their budget, however, the homeowners agreed to keep a close eye on the attic. After a couple of years, it became clear that the two small gable-end vents weren’t providing enough airflow to keep the attic cool and dry. In the summer, the temperature skyrocketed during the day and didn’t cool down in the evening. In the winter, moisture condensed on cold surfaces.