Monitor Points for condensation evaluation in brick wall

[steven]

I am not clear how to best set up monitoring points to evaluate the likelihood of condensation in a brick veneer exterior wall...

Exterior wall assembly: Brick veneer, Air space, fluid-appliled WRB, FG mat-faced exterior gypsum sheathing, metal studs, fiberglass batt insulation, poly vapor retarder, gypsum board, paint

I am interested in evaluating the likelihood of condensation at 2 locations: 1) the surface of interior poly vapor retarder, and 2) inner face of the exterior sheathing (as well as within the sheathing itself)

Re the vapor retarder: How do I evaluate the likelihood of condensation on the "surface" of a thin, relatively impermeable membrane like a vapor retarder? Do I place a monitoring point at the outermost grid element of the vapor retarder itself? Considering it's more or less impermeable does this accurately assess the likelihood of condensation on the "surface", or should I add a thin diagnostic layer in front of it, and if so, what would the diagnostic layer be (air/vapor retarder) and how do I evaluate the diagnostic layer (add monitor point and look at RH/Dew point graph)?

Re the exterior sheathing: I am concerned with two conditions - a) condensation on the inner "surface" of the sheathing, and b) condensation (or excessive moisture) within the sheathing. Re the "surface" condensation, do I treat it as above re the "surface" of the vapor retarder? Re the high moisture within the sheathing, do I look at the RH to ensure it doesn't reach 100 (or look at Temp and ensure it does not drop below dew point) via Graphs or Create Course; or should I look at Moisture Content graphs of the layer (if so, what are criteria for danger for a FG mat-faced gyp sheathing)?

Thanks for your help.

[Daniel]

Steven,

you have two different cases:

1. for a mostly vapor and water tight material put the monitor in the last grid element of the next material (in your case in the fibre insulation).

2. If you have a sheathing which can absorb the moisture and rech critical conditions you evaluate the moisture content in this material (normally for a thickness of 10 mm min).

If you want to evaluate the amount of condensation water you can divide the insulation layer in two - one with 1 cm thickness directly in contact with the vapor reatarder. Than you can evaluate the water content in this 1 cm thickness - all water above the free saturation water contetn is dew water.

best regards
Daniel