Published on February 7th, 2013 | by Henri


Plumbing vents should go through roof

Q.    We are doing a renovation that includes a new bathroom on our first floor. Today the carpenter mistakenly ran one of the plumbing vents up through our second floor roof, not far from the furnace chimney. (He was supposed to run it out the side of the building instead.)

Are there health or safety reasons that we should have him correct this error? The chimney stands a good deal higher than the vent, if that information is useful.

Thank you for any help you can give. I read your column avidly and remember you talking about the relative position of vents and chimneys at some point in the past.

A.    There is no safety risk there. And it’s better to run plumbing stack vents through a roof than through a wall where it could be close to a window or a soffit vent that could take the gases back into the attic.

You must be referring to my earlier mention of metal caps on chimneys with multiple flues. The wrong caps can cause the gases from one flue to be sucked down an adjacent flue with potentially disastrous results. Either tunnel-like caps set parallel to each other (not facing each other) or a wythe installed between two flat caps are ways to cap chimneys safely.

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