What Is a Passive House (PHIUS) Design?
Passive House (PHIUS+ in North America) is the ultra-low-energy building standard: heating/cooling demand under ~4.75 kBTU/sq ft/year, airtightness under 0.06 CFM50/sq ft, and the comfort requirements (no cold surfaces, even temperatures) that define the standard. The design is physics-driven: superinsulation, airtight envelopes, heat-recovery ventilation, and thermal-bridge-free detailing — modeled in WUFI Passive before construction. Certification requires third-party verification.
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The five principles
Continuous insulation (R-40+ walls, R-60+ roofs typical — the envelope does the heating), airtight construction (0.06 CFM50/sq ft — fifty times tighter than code — verified by blower-door testing), heat-recovery ventilation (the HRV/ERV is the lungs — balanced ventilation with 75%+ recovery), high-performance windows (U-0.14 or better, solar-optimized orientation), and thermal-bridge-free detailing (every steel penetration, every slab edge, thermally broken — the details are the standard).
Engineering the passive building
The energy model (WUFI Passive) sizes everything: the heating/cooling loads are so small that a mini-split or two conditions the whole house; the ventilation design (the HRV ductwork — short, straight, commissioned for balance); the moisture analysis (superinsulated assemblies need the vapor-profile design — the wrong membrane placement rots the wall); and the window optimization (solar gain vs. overheating — shading designed, not hoped). The MEP engineer designs for loads a tenth of conventional — the equipment shrinks dramatically.
Certification and cost
PHIUS+ certification: design review, construction verification (blower-door tests, the rater's inspections), and the final certification. Cost premium: 5-15% over code construction — the insulation, windows, and ventilation cost more; the tiny mechanical systems cost less. The payoff: 80-90% heating-energy reduction, unmatched comfort (no drafts, no cold spots), and resilience (the building holds temperature through outages). The standard keeps tightening — design for the current PHIUS+ version.
The bottom line
Passive House (PHIUS+) demands ~90% less heating energy via superinsulation, 0.06 CFM50 airtightness, HRV, and thermal-bridge-free details — modeled in WUFI Passive, verified by testing.
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