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Modified B-vent


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Here's a picture of a B-vent in an attic. It looks like the lower section was modified and screwed into the elbow. I've looked throught the Simpson installation instructions and don't see any mention of field modification. Is this allowed?

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And here's a pic of the B-vent at the attic floor. No firestopping and it's in direct contact with the framing.

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And yeah, there's a problem with drafting, too.

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You can use 1/4" galvanized screws, but you can't have a screw penetrate the inner liner. Screws for 3" and 8" pipe. In my Simpson guide, they actually recommend screws in some cases.

Elbows have to be strapped and supported; the elbow can't bear the weight of the pipe.

And, you got the combustible contact thing and no firestop. Which is stupid; Simpson makes a nice little transition plate for firestopping.

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  • 4 weeks later...

B-vent must be installed per the listing, which this is not. No listed firestop, no fireblocking per the code, no support at offset, single walled vent connector used in unconditioned space, inadequate clearance to combustibles and lack of draft hood connector for transition to single walled connector(recommended but not required for listing. As stated, you can screw at joint overlaps with 1/4" screws as long as they don't penetrate inner liner. Usually, what I find is the screw is too long and pushes the inner liner inwards like daisy petals thus restricting the vent.

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