How a Curtain Wall Works: The Complete Guide (2026)

The core principle: what makes a curtain wall non-load-bearing

A curtain wall is defined by what it does not carry. It never supports the building's floor slabs, roof or the weight of the storeys above it. The concrete or steel frame carries all vertical structural loads, and the curtain wall simply forms a protective outer envelope hung in front of that frame like a curtain - which is where the name comes from. Strip the glass away and the building still stands; strip a column away and it does not.

The wall must still resist several forces and hand them cleanly back to the structure:

• Dead load: its own self-weight. Aluminium and glass typically weigh 25 to 60 kg per square metre, carried down the mullions to dead-load anchors at each floor.
• Wind load: positive pressure and negative suction, designed to IS 875 Part 3 and the National Building Code of India (NBC) 2016 - often 1.0 to 2.5 kPa depending on building height, terrain category and local wind speed.
• Seismic and building movement: inter-storey drift is absorbed at the slab anchors and stack joints so the glass never cracks. Hyderabad sits in seismic Zone II, but tall towers are still designed for drift.
• Thermal movement: aluminium expands about 0.024 mm per metre per degree C, so expansion gaps are built into the mullion splices to cope with a 40-plus degree summer-to-monsoon temperature swing.

Because the frame behind takes the structural load, the facade can be almost entirely glass - an impossibility for a traditional load-bearing masonry wall, where openings are limited and the wall itself props up the floors.

How loads reach the structure: anchors and slab edges

Loads travel from the glass into the framing and out to the floor slabs through steel or aluminium anchor brackets bolted to the slab edge. Each mullion is tied back at every floor, with brackets typically spaced 1.2 to 1.5 m horizontally and adjustable in three directions to correct for the construction tolerances you always find in a poured concrete frame.

• Dead-load anchors: fixed brackets that carry each panel's weight vertically down into the slab.
• Wind-load anchors: slotted brackets that resist horizontal wind pressure and suction but allow vertical movement, so thermal expansion does not build up stress in the frame.
• Mullion stack joints: a spigot (sleeve) connection between vertical members lets each floor's section move independently, absorbing thermal and seismic drift without transferring it to the glass.

This arrangement means the glass and aluminium act only as a pressure-resisting membrane, while the real strength stays in the building frame behind it. Getting the anchor design and setting-out right is the single most important part of installation - a bracket set 15 mm out of tolerance can throw an entire vertical grid line off. That is why we survey and mark every slab edge before fabrication begins, a discipline that runs through all of our services on the facade side.

The frame and glass: what curtain wall panels are made of

The framing grid is built from aluminium extrusions, almost always alloy 6063-T6, chosen for its strength-to-weight ratio, corrosion resistance and clean extruded profiles. Mullion depth is sized to the wind span: 50 to 100 mm on low-rise facades and up to 200 to 250 mm on high-rise towers, with wall thicknesses of 2 to 3 mm. Deeper mullions resist more wind but use more aluminium per square metre, so the engineer balances performance against cost on every project.

• Glass: safety glass to IS 2553 - toughened (4 to 5 times stronger than annealed) or laminated for fall protection, in thicknesses of 6, 8, 10 or 12 mm.
• Insulated glass units (IGUs): two panes separated by a 12 to 16 mm air or argon gap deliver U-values of about 1.4 to 3.0 W/m2K, aiding compliance with the Energy Conservation Building Code (ECBC).
• Coatings: low-E and solar-control coatings cut solar heat gain (SHGC often 0.25 to 0.40), critical in Hyderabad's high-radiation summers where west-facing glass can otherwise turn offices into greenhouses.
• Spandrel panels: opaque insulated or back-painted glass conceals the floor slab, beams and building services between the vision-glass levels, so the elevation reads as continuous glass.
• Finish: framing is usually powder-coated or PVDF-coated aluminium, and anodised options resist Hyderabad's dust and pollution while holding colour for decades.

The choice between a captured system (with visible aluminium pressure caps) and a fully bonded structural glazing facade is largely aesthetic, but it changes the glass edge detailing, the silicone specification and the cost per square foot.

Keeping water and air out: the rain-screen principle

A curtain wall stays weathertight by managing water rather than trying to seal it out completely, using pressure equalisation and internal drainage. Gaskets and glazing seals form the first barrier, but any water that gets past is caught inside the framing and drained back out through weep holes at each transom - vital during a Hyderabad monsoon that can dump 100 mm of rain in a single day.

• Pressure equalisation: air chambers behind the outer seal balance wind pressure so rain is not driven inward through the joints.
• Drained-and-ventilated glazing pockets: channels collect any leakage and route it down to weep slots, then back to the outside face.
• Structural silicone joints: in structural glazing systems the glass is bonded to the frame with silicone designed to ASTM C1401, eliminating exterior metal caps while still shedding water.
• Air and water testing: completed walls are tested to standards such as ASTM E283 (air infiltration) and ASTM E331 (static water penetration), and sometimes AAMA field spray tests, before handover.

The most common cause of a leaking facade is not the glass but poor jointing at the transom-to-mullion intersections, so factory-controlled corner cleats and careful wet-seal detailing matter enormously. A well-built curtain wall glazing system treats every joint as a drainage path, not just a bead of sealant.

Stick vs unitized curtain wall systems compared

Curtain walls are installed in one of two ways - stick-built (assembled piece by piece on site) or unitized (large factory-made panels craned into place) - and the choice affects speed, quality and cost more than any other single decision.

• Stick system: mullions, transoms and glass are installed separately on site. Lower material and tooling cost, but slower and more weather-dependent, and best suited to low- and mid-rise buildings up to about 10 floors.
• Unitized system: storey-high panels are fabricated and glazed in a controlled factory, then hung on the slab anchors. Faster erection (a crew can hang a full floor in a day), far tighter quality control and much better for high-rise towers.
• Cost trade-off: stick systems carry lower factory setup but higher on-site labour and scaffolding cost; unitized systems have higher factory setup but slash site time, reduce weather delays and cut safety risk at height.
• Quality control: because unitized panels are glazed indoors, the critical silicone bonding happens in dust-free, temperature-controlled conditions - a real advantage in a dusty, humid city.

As an indicative figure, expect roughly INR 1,200 to 3,500 per square foot supplied and installed, depending on glass, framing depth, coatings and the system type. For most large projects in Telangana and Andhra Pradesh we recommend unitized for towers above 12 floors and stick for boutique commercial or residential facades where the elevation is broken up.

Curtain wall cost per square foot in Hyderabad

In Hyderabad a curtain wall typically costs INR 1,200 to 3,500 per square foot supplied and installed, and understanding what drives that range helps you budget realistically before you get a free quote. Price is not one number - it is the sum of several specification choices.

• Glass specification: single toughened glass sits at the lower end, while double-glazed low-E insulated units with premium solar-control coatings push toward the top of the range.
• Framing depth and system: deeper mullions for high wind spans and unitized fabrication add cost versus a shallow stick system on a low-rise building.
• Coatings and finish: PVDF and anodised finishes cost more than standard powder coating but last longer against Hyderabad's dust and UV.
• Height and access: taller buildings need cranes, more anchors and stricter engineering, all of which raise the per-square-foot rate.
• Hardware and junctions: entrance doors, canopies and spider-glazed lobbies within the facade carry their own hardware and fabrication cost.

As a rough planning guide, a mid-spec unitized office facade in Hyderabad or Secunderabad often lands around INR 2,000 to 2,800 per square foot, while a simple stick facade on a small commercial building can come in nearer INR 1,200 to 1,600. Always price against a proper wind analysis and glass performance spec, not a bare rate card.

Thermal performance and energy code in the Hyderabad climate

In a composite climate like Hyderabad's, a curtain wall's biggest job after keeping rain out is controlling heat. Glass is the weakest thermal link in any facade, so the specification here decides whether the building meets the Energy Conservation Building Code (ECBC) and keeps air-conditioning bills sane over a 25-year life.

• Solar heat gain coefficient (SHGC): aim for 0.25 to 0.40 on the east and west elevations that take the harshest morning and evening sun.
• U-value: double-glazed low-E units of 1.4 to 3.0 W/m2K sharply cut conductive heat gain compared with single glazing.
• Thermal breaks: polyamide strips inside the aluminium mullion stop heat bridging straight through the metal, reducing condensation risk on air-conditioned floors.
• Visible light transmission (VLT): balance daylight against glare - 40 to 60 percent VLT is a common sweet spot for offices, letting in usable light without a mirror-dark interior.

A well-specified curtain wall can cut a building's cooling load by 20 to 30 percent versus clear single glazing, paying back the premium glass cost within a few years on a Hyderabad or Secunderabad office tower. Orientation-tuned glass - a higher-performance coating on the west face than the north - is one of the cheapest ways to lift performance without redesigning the whole envelope.

Common curtain wall mistakes to avoid

Most facade failures trace back to a handful of avoidable errors, and knowing them helps you brief a contractor properly. On our sites across Telangana and Andhra Pradesh these are the issues we see most often on walls built by others.

• Ignoring slab-edge tolerance: skipping a proper survey before fabrication leads to anchors that will not line up, forcing on-site improvisation that weakens the wall.
• Under-designing wind load: using a generic mullion instead of one sized to IS 875 Part 3 for the building's real height and exposure invites deflection and glass stress.
• Treating joints as sealant-only: relying on a single external silicone bead instead of a drained, pressure-equalised joint is the number one cause of monsoon leaks.
• Wrong glass for orientation: putting the same low-spec glass on the west face as the north face drives up cooling load and glare.
• Site glazing in dusty or humid conditions: structural silicone bonded on a windy, dusty site rarely achieves its rated adhesion, which is a strong argument for unitized fabrication.
• Neglecting maintenance access: forgetting to plan a building maintenance unit (BMU) or anchor points means the facade cannot be cleaned or resealed safely later.

Maintenance, lifespan and choosing a curtain wall contractor

A well-designed aluminium and glass curtain wall lasts 40 to 50-plus years, but it is not fit-and-forget - the aluminium and glass outlive the sealants that keep the system weathertight. Planning for maintenance from day one protects the investment.

• Sealants and gaskets: silicone and EPDM seals are typically inspected and re-serviced at 20 to 25 years, before they fail rather than after.
• Cleaning and inspection: facade access via a BMU or rope access keeps glass clear and lets inspectors spot failed seals or slipped gaskets early.
• Hardware servicing: floor springs, closers and locks on integrated doors need periodic adjustment to keep entrances swinging smoothly.
• Warranty: reputable installers back framing and glazing workmanship for 5 to 10 years and processed glass separately under the glass maker's warranty.

Choosing an experienced local contractor matters because facade problems are expensive to fix at height. Hakimi Aluminium and Glass designs, fabricates and installs both stick and unitized aluminium-and-glass curtain wall glazing systems across Hyderabad, Secunderabad and the wider Telangana and Andhra Pradesh region. See the finished work in our recent projects, then get a free quote for your building.