High moisture storage materials exposed to solar radiation

[Dave Bryan]

When is it appropriate to model wall behavior with solar radiation on or off?

For wood cladding on R30 walls in U.S. climate zone 6 (cold, with most driving rain coming from the south) and with a 4 ach air gap behind the cladding, felt wrb & .5 perm interior vapor retarder, with radiation enabled the north exposure yields the wettest OSB sheathing. For metal cladding, orientation and whether the radiation function is on or off, makes little difference.

This all makes sense. But for fiber cement cladding, which can hold a lot of moisture, with radiation enabled for gray material, the 10 year sheathing humidity peaks at 99% and the mold isopleths are way above Lim II. Is this reasonable? Can WUFI adequately model claddings with high moisture storage exposed to solar radiation?

There also tend to be balance errors for most cases with solar radiation enabled.