Condensation on tenant walls. What to do?

[Isaak Brown]

Hi all, Thanks as always for any help and advice. Tenants are experiencing heavy condensation. Walls or damp to touch, and some clothes are now moldy. We've brought in two dehumidifiers which are helping, but I'm not sure what the root problem is or even who to ask for help. One contractor said moisture is coming through a hole in the exterior stucco, but another said no way because the vapor barrier would block it. 1st one recommended installing insulation, but I've also read this can increase condensation problems. Any experience with these issues? We're not even sure who to call to solve this problem! Isaak

[Roy N.]

@Isaak Brown

You first need to find the source.

What is the relative humidity in the unit?  What is the humidity level external to the building?

If there is high humidity in the unit and the walls are cold (below dew point) you will get condensation on the wall face.   This is a common winter issue up here in older buildings, with little to no insulation, when it gets cold and there is high indoor humidity.  I'd be surprised if it gets that cold down in Oakland, but you are likely dealing with higher indoor (and outdoor) humidity and the face of your wall assembly may drop below the dewpoint.

You need to find the cause of the humidity: broken dryer vent line; dishwasher; long, steamy showers w/o the bathroom fan running; water leak; too many people living in the unit; in-adequate ventilation (particularly if the envelope is tight); a grow-op in the basement, etc.  Once you find the cause you can plan the necessary steps to correct the problem.