ENVELOPES It is important for design teams and building owners to consider that cold air infiltration has a significant effect on heat loss through the external envelope and overall CO2


emissions of a building.


The air-tightness of a building is quantified in terms of its air permeability, which is defined as the volume flow rate of air per m2


applied pressure difference of 50 Pascal (Pa).


Compliance with the regulations is enforced through pre-completion testing. This is mandatory for all types of buildings. ATTMA TS: 2010 gives the methodology for air pressure testing. All buildings must be pressure tested, unless the floor area is less than 500m2


, when a default value of 15m3 /h/m2 for air-tightness is 10m3


can be used. For buildings over 500m2 /h/m2


.


Studies suggest that it will be difficult to meet the overall building CO2 emission rate without a reasonably air-tight building envelope.


Pre-finished steel is inherently air-tight. Air leakage will only occur through joints in the cladding system and unplanned gaps around the penetrations. Figure 4. Effects of insulation and air-tightness


10 m3 10 m3 /hr/m2 /hr/m2 Wall 0.25 Roof 0.15 -5% Wall 0.35 Roof 0.25 3 m3 /hr/m2 Wall 0.35 Roof 0.25 3 m3 15 Key


■Insulation ■Air-tightness


■Part L Backstop ■Combined


/hr/m2 Wall 0.25 Roof 0.15 20 25 Kg CO2/m2 /yr 30 35 -17%


When considering the detailing it is important to consider:


Joints and junctions within the metal envelope; between the metal envelope and other cladding materials, and with the floor slab


Planned penetrations, for which well- designed specifications should be given


Unplanned penetrations, such as for building services.


58


Expert guidance for design teams and building owners on the sealing of pre- finished steel cladding joints are given in the Colorcoat® Technical Paper.


Find out more about creating an air-tight building envelope.


a maximum reasonable design limit of building envelope, including the floor slab per hour at an


AIR-TIGHT BUILDING


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