Moisture/algae on sheathing/block at grade


Old 05-18-20, 12:36 PM
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Moisture/algae on sheathing/block at grade


The picture I have attached does not capture the worst affected areas with respect to moisture damage, but it does capture a combined concern; water damaging the sheathing and algae staining on block at grade.

What I have done in other areas of the house (this picture is the garage) is to replace the bottom 12 - 18" of sheathing with pressure treated plywood. I wrap the bottom edge of the PT ply with Grace roof membrane; so the back 2-3", bottom edge, and around 12" of the face of the ply are covered with the membrane.
I wonder if I should do anything more.
With respect to the green stuff that forms on the cement blocks, I'm wondering if it would be advisable to install a strip of copper or (more affordably) zinc under the bottom edge of the sheathing.
In case you're wondering what will cover the sheathing, I install 6" PVC "band-board", topped with aluminum Z-flash, and WRB overlapping the top of the Z-flash, prior to my first course of Hardie plank (a bit of that is visible at the right edge of the picture).

I should also note that much of the moisture damage that affected this particular part of the house/garage has been mitigated by adding kick-out flashing where the house abuts the garage--just over the doorway seen in the picture. However, this is the North side of the garage, so it gets little to no direct sunlight, plus, the "L" formed with the abutting house results in reduced air flow to the area.

Thanks in advance.
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Last edited by SturdyNail; 05-18-20 at 01:07 PM.
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