Glossary
ACH - Air changes per hour
Air barrier - The uninterrupted line defined within any section through the envelope of the dwelling which identifies the barrier to air leakage which is to be provided in the construction
Air leakage - The uncontrolled flow of air through gaps and cracks in the fabric of dwellings (sometimes referred to as infiltration, exfiltration or draughts)
Air Permeability - The physical property used to measure the airtightness of the building fabric. It is defined as air leakage rate per envelope area at the test reference pressure differential across the building envelope of 50 Pascal (50N/m2 )
Cavity barrier - A construction provided to close a concealed space against penetration of smoke or flame, or provided to restrict the movement of smoke or flame within such a space
Cavity closer - Masonry unit or plastics component that closes a cavity at the vertical sides of an opening
CPC - Carbon Performance Coefficient - the calculated carbon dioxide emission rate of the building divided by that of the reference dwelling in Building Regulations 2021 TGD-L (Dwellings) Appendix C
Dew point - The temperature at which air becomes saturated with vapour
EPC - Energy Performance Coefficient -the calculated primary energy consumption of the proposed dwelling divided by that of the reference dwelling, Building Regulations 2021 TGD-L (Dwellings), Appendix C
Key junction -The following types of junctions are considered key junctions where they include a heat loss plane element:
Floor to wall (includes party walls)
Wall to wall (corners & party walls)
Roof to wall (includes party walls)
Lintel above window/door
Sill below window
Window/door jamb
This list is not exhaustive. Any junction in the dwelling which has a relatively long length or a high rate of heat loss, or both, should be considered a key junction.
Appropriate airtightness sealant - Sealant should be fit for its intended use and meet guidance in Technical Guidance D-Materials and Workmanship
Appropriate airtightness tape - Tape fit for its intended use and meet guidance in Technical Guidance D-Materials and Workmanship
Interstitial condensation - Condensation within building elements
MPCPC - Maximum Permitted Carbon Performance Coefficient
MPEPC - Maximum Permitted Energy Performance Coefficient
Vapour control layer - (Water) vapour control layers should comply with I.S. EN 13984 or should be verified according to I.S. EN ISO 12572.
The vapour resistance of all vapour control layers should be determined in accordance with I.S. EN 1931 and I.S. EN ISO 12572.
Where polyethylene is used as a vapour control layer it should have a minimum thickness of 0,12 mm (500 gauge), and a minimum vapour resistance of 250 MNs/g.
Where other materials, or integral boards containing a vapour control layer are used, they shall comply with Part D of the building regulations and their suitability should be determined by a condensation risk analysis in accordance with I.S. EN ISO 13788 or I.S. EN ISO 15026.
Documents referred to
Building Regulations Part L 2021 - Technical Guidance Document L Conservation of Fuel and Energy – Dwellings
BRE Report BR 497, Conventions for calculating linear thermal transmittance and temperature factors, BRE, 2016
BRE Information Paper IP 1/06 – Assessing the effects of thermal bridging at junctions and around openings, 2006
ATTMA TS1 – Measuring air permeability of building envelopes, 2006 Edition
BRE Report BR 262 - Thermal insulation: avoiding risks (2002 edition)
I.S. EN ISO 9972:2015 - Thermal Performance of Buildings - Determination of Air Permeability of Buildings – Fan Pressurization Method
“BISRA” Guide 47/2013 Designing and constructing for airtightness
NSAI airtightness testing - D-IAB-007 Airtight Testing Scheme Master Document Rev 5
SEAI Domestic BER Technical Bulletin, July 2020
