Extremely humid interior atmosphere
We are currently working on a project in the Chicagoland area at a water reclamation district. We are re-roofing a building that enclosed the water filtration pools with extremely high levels of humidity.
We are installing a new roof membrane over the concrete topping slab on the roof and running vertical on the multi-wythe brick walls that serve as both parapets as well as extend up to a higher level than the adjacent roof. The roof membrane will be attached to an exterior grade plywood that is attached to the brick.
How do you recommend we treat the plywood to mitigate any vapor coming from the highly humid interior side of the brick? I can send a copy of the detail as well.
Thank you.
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Replies
Nathan,
If you can post an image showing the proposed detail, that would be useful.
It doesn't sound like the details on this building were well-thought-out. If this is a building with multi-wythe brick walls, here are a few questions:
1. How old is the building?
2. Are the walls insulated? If so, what type of insulation -- and is it interior or exterior insulation?
3. Is the roof insulated? If so, what type of insulation -- and is it interior or exterior insulation?
4. Do the bricks show signs of freeze/thaw damage?
Hi Martin,
Thanks for the input. Here are the answers to your questions. Any thoughts are greatly appreciated.
1. This building is a historic building and a portion of it dates back to 1874.
2. The walls are not insulated.
3. The roof is insulated with a vapor barrier. It is exterior insulation.
4. There has been recent work on the masonry outside of our scope of work.
I have attached an existing picture of the current roof installation as well as a detail for the new roof.
Thank you
Nathan,
As you probably realize, this building is very poorly insulated. Insulating the roof helps a little, but the parapets represent a massive thermal bridge.
As long as the exterior side of the parapets are exposed to the air, the humid bricks will dry to the exterior. So the plywood won't trap moisture.
You might as well specify pressure-treated plywood if you are worried that the bricks are damp. Pressure-treated plywood costs a little bit more, but the upcharge isn't too significant.