‘…the physical property used to measure airtightness of the building fabric. It is defined as air leakage rate per hour per square metre of envelope area at the test reference pressure differential of 50 pascals (50 N/m2). The envelope area, or measured part of the building, is the total area of all floors, walls and ceilings bordering the internal volume that is the subject of the pressure test. This includes walls and floors below external ground level. Overall internal dimensions are used to calculate this envelope area and no subtractions are made for the area of the junctions of internal walls, floors and ceilings with exterior walls, floors and ceilings.’
The limiting air permeability is the worst allowable air permeability.
The assessed air permeability is the value used in establishing the Dwelling Emission Rate (DER) and Dwelling Fabric Energy Efficiency (DFEE) rate and is based on specific measurement of the dwelling concerned or on measurements of other dwellings of the same dwelling type.
 Related articles on Designing Buildings Wiki
Featured articles and news
CEOs and high-level executives explain who they expect to be the most successful players in the future of construction.
What are package contracts and how are they broken down? Find out in our introductory article.
Identifying sustainable shoreline protection solutions in the face of rising sea levels and storms in the US.
Budget documents state modern methods of construction will be favoured for public infrastructure schemes from 2019.
A walk-through exhibition of an emergency humanitarian shelter is officially opened at BRE's Innovation Park.
How to work safely on a construction site during winter.
Housing is the big winner in Chancellor Philip Hammond's Autumn Budget.
The winner of our BSRIA competition, Tomorrow's challenges in today's buildings, is.... Bob Hendrikx. A big thank you to everyone that took part.
Committee of MPs accuses government of dealing billpayers a 'bad hand' over the guaranteed power price.
In 1992, the Joint Fire Code was first published. What influence does it still have on construction sites today?
"Companies will have to adapt or go out of business" - how are virtual reality and big data disrupting digital construction?
International Well Building Institute and BRE collaborate on multiple levels to advance human health through better buildings.
"The industry has tried moving away from prescriptivism to focus on performance, but maybe that’s no longer working".