Hygrothermal and Thermal Comfort Performance of Bamboo–Plastic Bricks in Tropical Informal Settlements: Multi-Scalar Simulation in BaSECo, Manila

Residents of informal settlements in Manila, Philippines, experience severe indoor heat stress and hygrothermal discomfort compounded by socioeconomic precarity. This paper evaluates a modular Bamboo–Plastic Brick (BPB), combining bamboo culms with 3D-printed recycled plastic frames, as a climate-responsive alternative to conventional Concrete Hollow Blocks (CHBs) for tropical informal housing. A multi-scalar computational assessment was conducted to evaluate its performance: steady-state 2D thermal analysis (THERM) evaluated heat flow and thermal bridging at the brick and brick-to-brick connection scale; dynamic hygrothermal simulation (WUFI) assessed moisture and heat transfer through the wall cross-section; and single-zone dynamic thermal simulation (IESVE) quantified indoor thermal comfort and humidity in a BaSECo residential unit. At the wall scale, the BPB’s stratigraphy provides effective hygrothermal defense: while the exterior face sustains seasonal moisture accumulation during the monsoon, the interior surface maintains a zero mold growth index year-round. At the zone scale, BPB maintains indoor relative humidity within the optimal 40–60% range for 4345 h (50% of the year), at low ventilation (1 ACH), significantly outperforming the CHB baseline of 29%. However, achieving adaptive thermal comfort requires maximizing natural ventilation to 10 ACH, at which point all envelope systems achieve thermal comfort for approximately 50% of the year. This reveals a fundamental operational trade-off in tropical passive design: the ventilation rates required for thermal comfort inherently compromise indoor humidity control, and vice versa. It is concluded that the BPB shows promising hygrothermal and thermal performance as an alternative to CHB when deployed with maximized natural ventilation, with its circular fabrication workflow addressed in a companion study.