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Rain screen detail on chimney box with brick veneer and flashing detail

mikkelsen | Posted in General Questions on

Building chimney box on peak of roof for chimney pipe and plumbing vent to exit. Thin brick veneer with a rain screen detail. The lid for the chimney box is elevated 1/2″ for an air gap with 3.5″ down turned legs for weather protection. All good so far, but when I go to install the step flashing on the roof next to the brick and then the cap flashing over that which it’s mortared into the grout line, there is now no more ventilation from the bottom of the rain screen as it has been sealed off with the flashing details.

Is this an issue?

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  1. GBA Editor
    Martin Holladay | | #1

    I've never installed thin brick veneer. My first piece of advice would be to follow the installation instructions provided by the veneer manufacturer.

    If these thin pieces of veneer are being glued to a substrate, where is the rainscreen? What material are you using to create a rainscreen gap?

    In general, rainscreen gaps have many virtues, and they are still valuable even if they are not fully ventilated at the top and the bottom. But if the type of veneer you are installing is not fully waterproof, and you are expecting some water to get past the cladding, then you will need to allow for drainage at the bottom of your rainscreen gap. That means that the step flashing needs to be integrated with the WRB at the interior side of your rainscreen gap.

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