When you split a facade elevation into spandrel and vision glass, you are drawing the line between what the building shows and what it hides. Vision glass is the transparent aperture that admits daylight and view; spandrel is the opaque module that masks the floor slab edge, the raised-floor and ceiling plenums, and the perimeter mechanical services between levels. Both occupy the same curtain wall grid and must read as a single continuous plane, yet they answer to completely different performance briefs, and the two are specified, priced and fabricated as separate products.
For the specifier the decision is rarely aesthetic alone. Spandrel height sets your floor-to-floor rhythm and hides structure; vision height sets daylight autonomy, view factor and your window-to-wall ratio (WWR), the number ECBC and NBC 2016 use to gate SHGC and U-value compliance. Get the split, the back-of-glass condition or the colour match wrong and you inherit thermal breakage, condensation, or a facade that looks patchy in raking light. This guide covers how to specify, detail and reconcile both zones, including realistic Hyderabad pricing and the spandrel glazing and curtain wall glazing detailing that keeps them reading as one wall.
The examples and rates here reflect what we see on live projects across Gachibowli, Kokapet, the Financial District and Hitec City, where high WWR towers, west-facing elevations and Telangana's summer heat load push both zones hard.
What is the difference between spandrel and vision glass?
Vision glass is a see-through insulated glass unit (IGU) delivering daylight, view and solar control. Spandrel is an opaque assembly, glass plus an applied back, that conceals the interstitial zone and completes the visual plane. They sit in the same curtain wall grid but do different jobs.
- Vision glass: optimised for VLT, SHGC and U-value; usually a double-glazed unit with a soft-coat low-E on surface 2.
- Spandrel glass: optimised for opacity, back-pan colour stability and thermal safety; a ceramic frit or applied opacifier provides the mask.
- Spandrel conceals: the slab edge, fire-stopping and perimeter smoke seal, HVAC returns, structural brackets and the raised-floor void.
- On a typical office floor plate, spandrel runs roughly 900 mm to 1,200 mm tall to cover the ceiling plenum plus the down-stand and slab; vision fills the balance to the head.
- On your drawings, dimension the vision aperture from finished floor. A 900 mm sill and 2,400 mm head is a common daylight-friendly split; adjust for the ceiling line and desk height so occupants get view without glare at the workplane.
How do you make spandrel and vision read as one facade?
The most common site complaint is that spandrel and vision panels look like different products. Reflection, not transmission, governs the match, so you control the outboard lite and everything behind it that changes the reflected tone.
- Specify the same glass substrate, thickness and coating on the outer lite of both zones so surface reflectance and colour align. A reflective glass facade is especially unforgiving of mismatch.
- Choose the spandrel mask type deliberately: ceramic frit (durable, opaque, integral) versus an applied opacifier or back-painted spandrel. Frit generally weathers and matches best.
- Match the back-pan or insulation colour to the intended reflected tone; a light back can shift the perceived glass colour by a visible degree.
- Keep the DGU facade build-up on the vision units consistent so the cavity does not tint one zone against the other.
- Mock up under raking sun before release. Hyderabad's low winter sun angles, roughly 40 to 45 degrees at midday in December, expose mismatch that overhead summer light hides.
- Keep sightlines, cap widths and gasket colour identical across both zones so the grid does not betray the split.
Why does spandrel glass break more often?
Spandrel glass runs hotter than vision glass because the back build-up, the insulation, back pan and trapped dead air, holds heat against the lite. That drives large centre-to-edge temperature gradients and thermal stress, and it is the single most common cause of spontaneous spandrel breakage in Indian towers.
- Specify heat-soaked toughened (thermally toughened, soak-tested) glass for spandrel to manage thermal stress and cut nickel-sulphide spontaneous breakage risk; toughening and heat-soak criteria fall under IS 2553. Our toughened glass work is heat-soaked as standard for spandrel runs.
- Keep insulation off the back face of monolithic spandrel glass. Maintain an air gap or use an insulated back pan, not insulation bonded directly to hot glass.
- Where a heat-strengthened or annealed lite is unavoidable, run a thermal stress analysis for the darkest-frit, highest-absorption case.
- In Telangana's summer peaks, ambient air hits 42 to 44 degrees C in April and May, and a dark spandrel back can push glass surface temperatures well past 80 degrees C, far above what the vision glass ever sees.
- Never assume the vision-glass build-up is safe for spandrel. Ask your fabricator to check high-absorption specialty glass cases separately.
What performance criteria go into the spec?
Spandrel is opaque wall; vision is a fenestration aperture. Compliance treats them separately, so schedule them separately in the glazing schedule and the energy model.
- Vision zone: state VLT, SHGC and U-value at the unit level. ECBC and NBC 2016 assess these against your WWR, and IGBC, GRIHA and LEED daylight and energy credits follow from them.
- Spandrel zone: state the assembly (opaque) U-value including back-pan insulation. This is your envelope's thermal contribution, not a glazing number, and a well-insulated spandrel back pan can reach U-values a fraction of the vision IGU.
- Structural: derive design wind pressure from IS 875 Part 3 for both zones; specify glass thickness and framing so member deflection stays within L/175 or 20 mm, whichever is less. Structural glazing sealant joints must be sized for the same load case.
- Acoustic: where a street or airside facade demands it, state a weighted sound reduction index (Rw) for the vision IGU; spandrel with insulation usually outperforms it.
- Water and air: reference ASTM E283 (air), E331 (water penetration) and E330 (structural) for the tested assembly.
- If you want an independent set of eyes on the numbers, facade consultancy and design-assist can catch a non-compliant WWR before it reaches the authority.
How do you decide the spandrel-to-vision split?
The split is a negotiation between structure, services, daylight and code, not a free aesthetic choice. Work it from the section, not the elevation.
- Start from the floor plate: measure the slab thickness, the down-stand beam, the ceiling plenum depth and the raised-floor void. The spandrel must cover all of it plus the perimeter fire seal, which usually lands the spandrel band at 900 to 1,200 mm.
- Then set the vision head as high as the ceiling allows for deep daylight, and the sill for view and furniture. Deeper floor plates in the Financial District and Kokapet towers benefit from a higher head to push daylight further inboard.
- Watch your WWR: a taller vision band raises solar gain and can breach ECBC SHGC limits, forcing a better (and costlier) low-E coating. A taller spandrel band lowers WWR but can make floors feel like bunkers.
- Consider the framing system. A unitized curtain wall prefabricates spandrel and vision into one factory-finished panel with tight colour control, which suits fast-track towers; a stick curtain wall is site-assembled and cheaper for low-rise but harder to colour-match on a windy elevation.
- Document the split as a typical bay and repeat it. Consistency across bays is what makes a facade read cleanly from Outer Ring Road distance.
Shadow boxes, interfaces and tolerances
A shadow box gives the depth and transparency of vision glass over a concealed zone, visually a hybrid but thermally a spandrel. Detail it as spandrel, not glazing, or it will fail.
- Ventilate the shadow-box cavity and use a matte, non-reflective back to prevent condensation and visible dust or streaking behind the clear lite. Hyderabad's dust and pre-monsoon humidity make unventilated cavities fog within a season.
- At the spandrel-to-vision transition, coordinate the slab-edge fire-stop and perimeter smoke seal. This interface is a common water and acoustic weak point and the first place a facade leaks in the monsoon.
- Allow for differential movement: thermal expansion and live-load slab deflection must not transfer into the vision IGU edge seal.
- Fabrication and setting-out tolerances stack. Hold glass size, bite and joint width tight so the plane stays flush across zones; a 2 mm creep per panel is visible across a ten-storey run.
- See how these details resolve on completed elevations in our project gallery, which covers unitized and structural-glazed facades across Telangana.
- Hakimi Aluminium and Glass provides design-assist, shop drawings, fabrication and installation for architects across Hyderabad, Secunderabad, Telangana and Andhra Pradesh, useful when reconciling spandrel colour match and shadow-box detailing early rather than on site.
What does spandrel vs vision glass cost in Hyderabad?
Both zones are priced per square metre of finished, installed facade, and the numbers below are indicative Hyderabad market rates for 2026. They move with glass coating, panel size, height and system choice, so treat them as a briefing range, not a quote.
- Vision IGU (double-glazed, soft-coat low-E, structural-glazed): roughly Rs 2,200 to Rs 3,800 per sq ft installed, depending on coating grade and DGU cavity.
- Spandrel glass (heat-soaked toughened, ceramic frit, insulated back pan): roughly Rs 1,600 to Rs 2,600 per sq ft installed. Frit and heat-soak add cost but the opaque unit skips the second low-E lite.
- Shadow box: expect a premium over plain spandrel, around Rs 2,400 to Rs 3,400 per sq ft, because of the extra clear lite, cavity ventilation and matte back.
- Unitized systems carry a higher rate than stick but recover it in faster erection and fewer site defects on tall towers; the crossover typically favours unitized above eight to ten storeys.
- For a bay-by-bay estimate against your actual elevation and glass schedule, get a free quote with your drawings and we will price spandrel and vision separately so you can value-engineer the split.
- Budgeting tip: over-specifying vision area to look impressive is the most expensive mistake, because every extra square metre of high-performance IGU costs more than the spandrel it replaces and adds cooling load for the life of the building.
Common spandrel and vision specification mistakes
Most spandrel-vision problems trace back to a handful of avoidable specification errors. Catch these at design stage and the facade behaves.
- Matching the transmitted colour instead of the reflected one, so the zones look right in the sample box and wrong on the tower.
- Using annealed or non-soaked spandrel glass to save cost, then losing panels to thermal and nickel-sulphide breakage two summers later.
- Bonding insulation directly to the back of monolithic spandrel glass and cooking the lite.
- Counting spandrel area in the WWR, which understates the real fenestration ratio and produces a non-compliant SHGC in the energy model.
- Detailing a shadow box as vision glazing, then chasing condensation and dust behind the glass for the life of the building.
- Ignoring the slab-edge fire and smoke seal at the transition, which is both a code failure and a leak path in the first monsoon.
- Leaving colour approval to a midday mock-up and never checking raking winter sun, when Hyderabad's low December sun angle is exactly when mismatch shows.
