Double Glazing vs Single Glazing for Commercial Buildings

The comparison that gets made badly

A DGU is routinely presented as "better glass" and single glazing as "the value option", and the discussion stops there.

The useful framing is different. In a cooling-dominated climate, most of the heat arriving through a window is solar radiation, not conduction. That is controlled by the coating. The cavity controls the conducted portion. A serious comparison looks at both, and at what the building actually needs.

Side by side

Factor	Double-glazed unit	Single glazing
Conducted heat transfer	Much lower	High
Solar heat gain	Determined by coating	Determined by coating
Acoustic performance	Better, especially unequal panes	Limited
Condensation risk on inner face	Low	High in humid, cooled buildings
Weight	Roughly double plus spacer	Lower
Thickness	Greater — frame must suit	Lower
First cost	Higher	Lower
Running cost impact	Lower cooling load	Higher cooling load
Seal life	Edge seal is a service-life item	No seal to fail
Frame requirement	System designed for DGU	Lighter systems adequate

Where each number does its work

SHGC — the fraction of solar energy transmitted — is the figure that moves the air conditioning load on a sunlit elevation. Lower is cooler, but push it too far with the wrong product and the interior gets dark or the glass becomes strongly reflective, which affects both the occupants and the neighbours.

U-factor describes conducted heat flow. This is where the cavity earns its place, and it is also what keeps the inner pane near room temperature — which is why a DGU largely removes the condensation problem that single glazing has in humid, air-conditioned buildings.

Visible light transmission is the third number, and it is the one forgotten in value engineering. A facade optimised only for heat can produce an interior that needs artificial light all day, which moves the energy cost rather than removing it.

ECBC 2017 frames the requirement as performance figures for the envelope, so the question for any project is what U-factor and SHGC the assembly must achieve — a matter for the project's energy consultant.

The edge seal is a real service-life consideration

A DGU depends on a sealed cavity. If the edge seal fails, moisture enters and the unit fogs internally — and a fogged unit is replaced, not repaired.

This is a manufacturing and handling quality issue, addressed by standards such as IS 16231 and EN 1279 for insulating glass units. It is worth asking for the unit's conformity evidence and the spacer specification, because a warm-edge spacer improves both the thermal performance at the edge and the condensation behaviour there.

Mistakes that cost real money

• Comparing U-value only. On a sunlit Indian facade, SHGC usually matters more.
• Specifying a DGU with clear glass and expecting performance. Without an appropriate coating, the solar gain path is barely addressed.
• Substituting single for double late in the project. The framing system, hardware and structural design were sized for a different unit.
• Forgetting visible light transmission. A dark facade that needs lights on all day has moved the problem, not solved it.
• Using equal pane thicknesses where acoustics matter. Different thicknesses perform noticeably better.
• Ignoring the installation and drainage detail. A DGU sitting in a rebate that holds water will fail at the edge seal early, whatever its quality.

Standards referenced

Envelope performance requirements in ECBC 2017; insulating glass unit standards IS 16231 and EN 1279; wind loading to IS 875 (Part 3). The required U-factor and SHGC for a specific building, and the structural adequacy of the glazing and its framing, must be established by the project's facade and energy consultants.