Airtightness Planning & Blower Door Testing Guide | SerVilla

In passive house engineering, airtightness is not an aesthetic preference; it represents the most uncompromising structural physics benchmark determining building durability and energy conservation. Contrary to the outdated myth that "houses must breathe through structural walls," uncontrolled air infiltration introduces convective moisture into structural cavities. In a high-performance home, air exchange is handled mechanically and continuously via 90%+ efficient filtered MVHR systems, while the building shell must rigorously verify n₅₀ ≤ 0.60 h⁻¹ under differential pressure testing.

1. Physics Behind the n₅₀ ≤ 0.60 h⁻¹ Standard: Convective Moisture Damage

Air leakage causes orders of magnitude more moisture damage than vapor diffusion:

• Comparative Physical Flow: Over an entire winter season, water vapor diffusion through a solid 1 m² plasterboard wall transports merely a few grams of water. By contrast, a tiny 1 mm continuous crack transports hundreds of grams of moisture daily via convective air currents!
• Interstitial Condensation Risk: Warm, moist indoor air driven through crevices cools rapidly against cold exterior sheathing, depositing liquid water within rockwool insulation and initiating framing degradation.
• The Strict Passive House Limit: At a pressure differential of 50 Pascals, the hourly volume of air escaping or infiltrating the envelope must not exceed 60% of internal net air volume (n₅₀ ≤ 0.60 h⁻¹]. SerVilla production builds regularly achieve field test results between 0.25 and 0.45 h⁻¹.

2. Intelligent Variable-Permeance Vapor Checks (Dynamic s_d-Values]

Rather than impermeable polyethylene foils, SerVilla specifies intelligent polyamide vapor-control membranes on the warm interior face of steel framing:

• Winter Resistance (s_d ≥ 5.0 m]: Interior air is warm and humid; the membrane pores remain tightly closed, preventing vapor from migrating into the cold wall cavity.
• Summer Drying Permeability (s_d ≤ 0.2 m]: Under reverse vapor drive in hot humid summers, the membrane molecular structure relaxes, allowing any trapped moisture to dry harmlessly back toward the interior.

3. Critical Penetration Details: Sealing Pipes, Ducts and Chassis Junctions

4. Blower Door Testing Protocols: ISO 9972 Method 1 vs Method 2

Differential pressure testing is executed using an airtight door frame assembly, calibrated variable-speed fan, and multi-channel digital micro-manometers:

• Preparation Standards: All external windows and doors are latched. MVHR supply/exhaust terminals, radon sumps, and drainage traps are temporarily sealed. Interior doors are propped open to form a single undivided air volume.
• Testing Progression: The fan generates step-wise differential pressures from 10 to 60 Pa across both depressurization and pressurization cycles. The leakage air flow rate at 50 Pa (V₅₀] is divided by internal net volume (V_n]:

• Regulatory Compliance: Test certificates conforming to ISO 9972 Method 1 are submitted for municipal building occupancy permits and Passivhaus Institut quality certification.

5. Real-Time Leakage Detection: Thermal Anemometers, Smoke Pens & Thermography

During the negative pressure stage (depressurization at 50 Pa], outside air rushes through any microscopic gaps:

• Thermal Smoke Pencils: Emitting dense, non-toxic chemical vapor to visualize localized air turbulence around service penetrations or electrical boxes.
• Infrared Thermographic Cameras: In cold weather testing, incoming ambient infiltration appears as distinct dark blue thermal plumes on thermograms, allowing trades to rectify defects prior to closing interior drywall linings.