Design Solution · Building Envelope
Design Solution · Dream about it
Tight envelope and QA delivering measured Passivhaus airtightness.
Rigorous detailing, site supervision and testing deliver very low air leakage, which is essential to reach measured Passivhaus performance. High airtightness cuts uncontrolled heat loss and ensures ventilation heat recovery actually works.
Airtightness is the measure that distinguishes a building that performs as designed from one that performs as assumed: mechanical ventilation heat recovery, for which Passivhaus is critically dependent, delivers its rated efficiency only when the envelope is tight enough to force air through the heat exchanger rather than leaking around it. Passivhaus targets typically require air permeability below 0.6 air changes per hour at 50 Pa, which is an order of magnitude tighter than Building Regulations Part L and demands a step-change in site practice — continuous air barrier detailing, trade sequencing discipline, and intermediate blower-door tests during construction rather than a single test at handover. This is not a novel technology but a quality system, and its track record in certified Passivhaus buildings is solid; the risk is not the concept but the procurement and supervision chain required to deliver it, particularly on a school project where multiple subcontract trades work across the air barrier. No provided evidence sits on this record, so the specific airtightness result is claimed rather than measured. The specifier's question is whether the QA regime — detailing standards, intermediate testing intervals, defect-remediation protocols — is fully specified in the contract documents and is being supervised by someone with Passivhaus site experience, because a tight envelope requires management at the trade interface, not inspection after the fact.
#airtightness #quality assurance #passivhaus