Air pressure n50 test
The n50-value over one hour is used by the Passivhaus standard to describe the number of air changes that occur within a building's envelope at a pressure difference of 50 Pascals (Pa). The Passivhaus standard is based on a building physics principle that a building can be heated only by the occupants' activities and solar gains. As such the standard is primarily interested in the volume of air that needs to be heated and thus the rate at which that volume of air would be replenished through uncontrolled ventilation or minimised through air tightness.
This is measured through an n50 pressure test which is carried out by closing and sealing doors and windows and installing a door blower to create a pressure differential of 50 Pa (equivalent to a 5 mm water column) between the inside and outside to measure the air change rate. The standard (or n50) requires a test result which is less than 0.6 air changes per hour @ 50 Pascals expressed as < 0.6h-1@50pa. Note that the volume of the building is based on the sum volume of all individual rooms rather than the total volume within the envelope.
[edit] Related articles on Designing Buildings
- Accredited construction details ACDs.
- Air change rates.
- Air permeability testing.
- Air tightness in buildings
- Airtightness of energy efficient buildings.
- Draughts in buildings.
- Energy audit.
- Floor plenum airtightness.
- Indoor air quality.
- Indoor air velocity.
- Passivhaus.
- Site inspections.
- Thermographic survey.
- The history of non-domestic air tightness testing.
Featured articles and news
Key points for construction at a glance with industry reactions.
Functionality, visibility and sustainability
The simpler approach to specification.
Architects, architecture, buildings, and inspiration in film
The close ties between makers and the movies, with our long list of suggested viewing.
SELECT three-point plan for action issued to MSPs
Call for Scottish regulation, green skills and recognition of electrotechnical industry as part of a manifesto for Scottish Parliamentary elections.
UCEM becomes the University of the Built Environment
Major milestone in its 106-year history, follows recent merger with London School of Architecture (LSE).
Professional practical experience for Architects in training
The long process to transform the nature of education and professional practical experience in the Architecture profession following recent reports.
A people-first approach to retrofit
Moving away from the destructive paradigm of fabric-first.
International Electrician Day, 10 June 2025
Celebrating the role of electrical engineers from André-Marie Amperè, today and for the future.
New guide for clients launched at Houses of Parliament
'There has never been a more important time for clients to step up and ...ask the right questions'
The impact of recycled slate tiles
Innovation across the decades.
EPC changes for existing buildings
Changes and their context as the new RdSAP methodology comes into use from 15 June.
Skills England publishes Sector skills needs assessments
Priority areas relating to the built environment highlighted and described in brief.
BSRIA HVAC Market Watch - May 2025 Edition
Heat Pump Market Outlook: Policy, Performance & Refrigerant Trends for 2025–2028.
Committing to EDI in construction with CIOB
Built Environment professional bodies deepen commitment to EDI with two new signatories: CIAT and CICES.
Government Grenfell progress report at a glance
Line by line recomendation overview, with links to more details.
An engaging and lively review of his professional life.
Sustainable heating for listed buildings
A problem that needs to be approached intelligently.
50th Golden anniversary ECA Edmundson apprentice award
Deadline for entries has been extended to Friday 27 June, so don't miss out!
CIAT at the London Festival of Architecture
Designing for Everyone: Breaking Barriers in Inclusive Architecture.
Mixed reactions to apprenticeship and skills reform 2025
A 'welcome shift' for some and a 'backwards step' for others.