UPVC Windows and Double Glazing

Windows are the weakest link in a building's thermal envelope, and in a typical apartment they account for a substantial share of total energy loss. UPVC profiles, with their multi-chamber structure and the low conductivity of the polymer itself, outperform aluminium frames without thermal breaks and older steel windows. Profiles come with three to seven chambers; five chambers is a balanced choice for Tehran's climate, while seven is mainly justified in colder regions.

What buyers most often overlook is the steel reinforcement inside the profile. UPVC alone lacks the stiffness to carry wind load and glass weight, so a galvanised section at least 1.5 mm thick must be inserted into each profile. A window with omitted or thinned reinforcement warps within a few years, sashes bind and the weather seal fails. Wall thickness of the profile matters too: Class A requires at least 2.8 mm, Class B at least 2.5 mm.

For glazing, the standard build-ups are 4+12+4 or 4+16+4 mm, giving a U-value of roughly 2.7 W/m2.K. Low-emissivity glass with argon fill brings that down to about 1.6 to 1.8. For acoustic performance, using two different glass thicknesses, say 4 and 6 mm, works better than two equal panes because the two leaves no longer share a resonant frequency.

The common installation error is fitting frames without proper packers and without correctly foaming the perimeter joint. A gap filled with plaster alone becomes both a thermal bridge and a water path. Another check is the presence of drainage slots in the bottom frame; without them water collects inside the profile and corrodes the hardware.