Sustainable Building Glossary

Adaptability in the long term: The main use/purpose of a building often changes during its lifespan and thus the design and materials must be adaptable for this without great disruption or cost. The simpler the house design and its services and the greater the thermal and moisture capacity of the building the easier this will be. In particular vapour open constructions with simple insulation and air tightness layers are easy to adapt and traditional building materials such as timber, blocks, renders etc. and products traditionally made out of it have been time proven to suit these requirements. Building in thermal capacity and moisture buffering assists the success of internal and service alterations.

Air changes per hour (ACH): The ACH (also air change value) is like the air permeability a measure of infiltration (unplanned air changes) used for energy calculations to indicate the performance of a building in terms of both energy use and fabric integrity. It indicates how often the entire air quantity in a building is renewed within one hour without any ventilation in place¹ [m³ m^-3 h^-1], also [h^-1]. It is calculated by creating a particular pressure difference between the outside and inside of the building when all intentional openings and ventilation systems are closed and by then measuring the amount of air that leaks through the external structure. The standard² pressure difference is 50 Pascal. For EnEV³ buildings without MVHR an AHC of 3 m³/m³/h (c.p. footnote⁴) and for Passivhaus an AHC of 0.6 m³/m³/h is accepted as the maximum.

Air Permeability: The air permeability is like the ACH a measure of infiltration (unplanned air changes) to indicate the performance of a building in terms of both energy use and fabric integrity. It indicates the cubic metres of air leakage per square metre of external area of the building per hour - [m³ m^-2 h^-1]. It is calculated by creating a particular pressure difference between the outside and inside of the building when all intentional openings and ventilation systems are closed and by then measuring the amount of air that leaks through the external structure. The standard² pressure difference is 50 Pascal. In Part L Building Regulations an air permeability of 10 m³/m²/h, for EST best practice for CSH level 3 an air permeability of 3 m³/m²/h, for higher CSH levels an air permeability of 1 m³/m²/h is accepted as the maximum.

Air tightness test: Also called Blower-Door-Test. Measurement of air changes per hour or air permeability. During this test areas of air leakage can be identified by using smoke guns and other means.

Air tightness: Through statutory air tightness requirements for the building shell, i.e. in Building Regulations, Code for Sustainable Homes, DIN⁵ 4108, EnEV³ or SIA⁶ 180, energy losses in the form of convection of warm air is prevented. See also air changes per hour, air permeability, dew point and air tightness test.

Approvals: Building Regulations set the standards which have to be met. The approvals are ways of showing compliance. This can be done by providing data and evidence of a specific type for a specific project, so that for instance, a building company would get approvals contract by contract for non standard ways of building (including traditional timber construction with wattle and daub infill, wychert construction, shallow flexible lime mortared footings etc). The company has to produced evidence from laboratories, suppliers and engineers. More easy is to get a generic approval. The basic ways are BBA, BRE certification (similar to BBA), LANTAC (which applies to all local authorities in England and Wales) or the use of European certifications⁷. Only BBA and BRE are accepted by NHBC and some other insurance and mortgage companies.