Transcription of Technical Note No. 12 SPECIFICATION OF HERMETICALLY …
1 CWCT 2000 January 2000 This document has been printed from the CWCT Cladding Forum , access to which is restricted to subscribing Members ofthe Centre for Window & Cladding Technology. Information about the availability of CWCT publications and membership isavailable at our website or from the address at the end of this Note No. 12 SPECIFICATION OF HERMETICALLY -SEALEDGLASS UNITSI ntroductionAn insulating glass unit is two or more panes ofglass spaced apart and sealed in a factory withdry air in the unit cavity. The air may then beflushed out and replaced with a range of othergases to improve thermal or acousticperformance. The SPECIFICATION of hermeticallysealed glass units is not always astraightforward matter; there are many issues inthe design and manufacture of these componentsthat are often overlooked or simplymisunderstood. The appropriate BritishStandard, BS 5713, fails to guide the specifier inany meaningful way.
2 This note lists the itemsthat the specifier might need to consider andpossible units are now used primarily to limit heatloss from a building - Approved document L ofthe Building Regulations, which limits glazedareas according to the thermal transmittancecoefficient ( U value) of the glazing, virtuallynecessitates their thermal performance varies with the widthof cavity, whether the cavity is filled with air orgas and the type of glass. Table 1 showsapproximate U values for a range of glazingunits. Plain float glass is assumed except whereindicated well as reducing heat loss, double glazing: Reduces condensation, which can occurwhen warm, damp air inside a room comesinto contact with a cold window pane; Reduces noise transmission, depending on,for example, the thickness and relativethicknesses of the panes, and cavity of glazingU value(W/m2K) 6mm air 12mm air 16mm air 20mm air 12mm argon low E glass 12mm 12mm air low E glass 12mm low E glass 12mm 1 U-values of different glazing unitsComponentsGlass units comprise the following elements:1 Glass (any type can be used includingwired and patterned);2 Spacer bar - maintains the space betweenthe panes and contains desiccant to keepthe air or other gas dry.
