On a recent CLT retrofit in Seattle, WUFI shows safe moisture at a balcony penetration that THERM flags as a cold bridge around 0.06 W/m·K; before I go down a rabbit hole, how are you aligning hygrothermal and 2D conduction results early without over-modeling? I’m trying to keep the assembly durable and low-carbon while still hitting a sub-25 kBtu/sf·yr target.
And i align them by taking THERM’s min interior surface temp/fRsi and using it as the interior BC in a quick WUFI‑1D of the local stack — “treat the 2D joint as a boundary condition” — then if fRsi < about 0.72 I add a thin thermal break or wrap the exterior insulation across the connector and rerun monthly, not hourly. What interior RH and rain leakage fraction are you assuming for Seattle?
I’d bound it by converting the 0.06 W/m·K into an fRsi check (ISO 13788; quick refresher: https://passivehouse.com/02_informations/03_thermal-bridges.html) to set a safe indoor RH, then in WUFI-1D keep normal BCs but add a small periodic “rain leak” at the penetration for Seattle splashback; if the CLT stays under about 20% MC you’re likely fine. Tiny caveat: that leak pulse drives more risk than the conductive hit — treat the balcony like a bad roommate and budget its mess early. What fRsi are you seeing in THERM, @OP?
But for balancing WUFI and THERM, I’ve found it helpful to initially run a simplified WUFI model with conservative humidity assumptions to see how it aligns before diving deeper. When you’re targeting that sub-25 kBtu/sf·yr, it can be crucial to adjust your expectations based on those early insights. Have you tried tweaking the internal RH settings to see if that affects your cold bridge readings?