A glass specification guide for architects starts with one discipline: specify a performance system, not a product - coating, substrate, interlayer, cavity, spacer, sealant and hardware acting together, not a single material named on a schedule. This guide gives you the language, criteria and Indian standards to write a glass specification that a fabricator can price accurately and build without guesswork, so your design intent survives from drawing to installed facade.
The method is to specify by measurable performance and let the supply chain engineer the exact make-up. Fix the numbers that matter - SHGC, U-value, VLT, acoustic Rw, thickness build-up, safety class and tolerances - reference the governing standards, and define every interface where glass meets frame, slab or another trade. In Hyderabad and Secunderabad's hot, high-solar climate the solar and daylight numbers usually carry the most weight, but structural, safety and acoustic criteria are what keep a specification defensible in front of a client or a facade consultant.
Below we walk through each performance criterion, the IGU make-up, structural and safety rules, the hardware that decides whether the glazing actually opens and seals, realistic Hyderabad budgets, and a pre-issue checklist. Where it helps, we point to how we deliver structural glass and facade work and toughened glass fabrication, so you can validate buildability early rather than at tender.
Performance criteria: the numbers that belong on your glazing schedule
Specify these against every glazing type, with target values and a test or standard basis rather than a brand. These five numbers are the backbone of any credible glass specification, and each should carry both a target and a tolerance.
- U-value (W/m2K): whole-unit thermal transmittance. Insulated glass units (IGUs / DGUs) with low-E coatings and argon fill reach markedly lower U-values than monolithic glass; align targets with ECBC and any IGBC, GRIHA or LEED credit you are chasing. A well-built sealed DGU can bring the unit U-value below 1.8 W/m2K.
- SHGC (0-1): fraction of solar heat transmitted. For Hyderabad and Secunderabad orientations with high solar exposure, low-SHGC coatings (often 0.25-0.30) cut cooling load; pair with external shading rather than pushing VLT to zero and killing daylight.
- VLT (%): visible light transmittance, which governs daylight and views. High-selectivity coatings deliver high VLT with low SHGC - call out the light-to-solar-gain ratio (LSG) if daylighting is a project driver, since an LSG above 1.5 is the mark of a genuinely selective coating.
- Acoustic Rw (dB): weighted sound reduction index for the full unit, achieved with laminated interlayers (e.g. acoustic PVB) and asymmetric lites. Specify Rw for the IGU, not a single pane - a good acoustic DGU can reach Rw 38-42 dB.
- Reflection and colour: external reflectance (%) and a colour reference, to control glare on neighbours and keep facade appearance consistent across batches and elevations. When you write these into the schedule, bidders can propose an equal-or-better make-up that you verify against numbers rather than marketing.
Structural and safety specification to IS 875 and IS 2553
Glass is a structural element under wind and impact; specify it that way, not as a finish. Getting the structural basis wrong is the single most expensive mistake in facade specification, because it surfaces only after installation.
- Wind load: derive the design wind pressure from IS 875 Part 3 and NBC 2016 for the building's height, terrain category and location, then size glass thickness and the IGU build-up to suit. Do not fix thickness before this calculation - a 1500 x 2400 mm pane on a 40 m tower in an open-terrain part of the Hyderabad outskirts sees a very different pressure from the same pane on a sheltered Secunderabad street.
- Deflection: limit centre-of-glass deflection (commonly L/175, or the manufacturer's serviceability limit) so glass, seals and interfaces are not overstressed and the facade does not read as 'oil-canned'.
- Safety glass: in human-impact zones - doors and side panels, low sills, full-height and balustrade glazing - specify toughened (tempered) or laminated safety glass to IS 2553. State the class explicitly on the drawing; do not leave it implied by location.
- Fragmentation and post-breakage: use laminated glass where retained fragments matter (overhead, balustrades, security). Toughened glass alone fragments into blunt dice and clears the opening, which is unacceptable overhead. Combining toughened and laminated processing lets you mix safety classes across a single elevation without changing supplier.
- Thermal safety: check thermal-stress risk on high-absorptance or partially shaded panes and heat-strengthen or toughen to prevent thermal breakage - a real risk on Hyderabad's south and west elevations, where shadow lines from deep reveals cross the glass through the afternoon.
The IGU / DGU make-up and interfaces
Describe the full build-up so there is no ambiguity in fabrication. Ambiguity here is exactly where cost overruns and disputes live, because every party fills the gap with its own cheapest interpretation.
- Build-up notation: outboard lite / cavity / inboard lite, e.g. 6 mm low-E toughened + 12 mm argon cavity + 6 mm clear laminated (6.38). State the coating surface (usually surface 2 for solar control).
- Spacer and edge seal: warm-edge vs aluminium spacer, and the primary (PIB) and secondary seal type - these govern edge U-value, condensation resistance, durability and warranty.
- Glazing method: structural silicone, captured / pressure-plate, or point-fixed, with the correct structural and weather sealant and a defined interface to the aluminium system. Point-fixed and spider-glazed facades rely entirely on fittings rated for the panel weight and wind uplift.
- Interfaces: define glass-to-frame edge cover and bite, the slab edge and spandrel condition, and the junction with adjacent trades (waterproofing, cladding). Most facade failures start at interfaces, not in the glass itself.
- Compatibility: require written sealant / interlayer / coating compatibility confirmation from the supplier to avoid delamination and seal failure. If you are unsure how a chosen build-up will detail against your frame, get a free quote with your section attached and we will mark up the bite and drainage before you tender.
Hardware, fittings and glazing systems the spec must name
A glass specification that stops at the pane is only half a specification. The hardware decides whether a door swings true, a shower stays dry and a facade drains - and it is where value-engineering quietly substitutes weaker parts unless you name grades, load classes and finishes.
- Frameless doors and entrances: specify patch fittings, floor springs and door closers by load class and finish, matching the closer body size to the leaf weight so a 12 mm toughened door does not sag over time. As authorised dealers for Taiton, Enox and Ozone across Hyderabad and Secunderabad, we can size these accurately against your leaf schedule.
- Handles, locks and access: call out handles, locks and access hardware with the finish and backset stated, so ironmongery reads consistently across the whole project rather than opening by opening.
- Sliding and partition systems: for large openings, specify sliding gear rated to the sash weight, and for interiors coordinate partition systems with the glass thickness and acoustic target so the Rw you specified is not undone at the frame.
- Wet areas and balustrades: shower enclosures need corrosion-resistant hinges and seals, and railing clamps and standoffs must be sized to the balustrade load case, not chosen on looks alone. Specify the glass as toughened to IS 2553 and the hardware finish to suit.
You can see how hardware and glass come together on our recent projects, or list the specific fittings against each opening on the schedule so nothing is left to site interpretation. Reviewing the full range across our services early also flags any long-lead item before it delays glazing.
Realistic Hyderabad budgets: what performance glazing costs
Give your client honest ranges early. These are indicative installed rates in the Hyderabad, Secunderabad and wider Telangana / Andhra Pradesh market as of 2026, and should be confirmed against the final build-up, quantity and site access.
- Single toughened glazing (10-12 mm, framed): roughly INR 350-650 per sq ft supplied and fitted, before hardware.
- Performance DGU with low-E solar-control coating: typically INR 850-1,400 per sq ft installed, depending on coating selectivity, argon fill and spacer type.
- Structural silicone glazed (SSG) or spider / point-fixed facades: commonly INR 1,400-2,200 per sq ft installed once fittings, sealant and engineering are counted.
- Acoustic DGU targeting Rw 38-42 dB: expect a 15-30% premium over a standard DGU because of the laminated acoustic interlayer and asymmetric lites.
- Frameless door hardware sets (patch fittings, floor spring, handle, lock): often INR 12,000-30,000 per door depending on the Taiton, Enox or Ozone range and finish.
The cheapest quote is rarely the cheapest facade over ten years - a failed edge seal or an undersized floor spring costs far more to rectify than to specify correctly. Compare like-for-like build-ups and hardware grades, not just headline rates, and if you want a delivered-cost view early you can get a free quote against your draft schedule.
Process and timeline: from spec to installed facade
Even a perfect specification fails if the programme ignores fabrication and approval lead times. Build these stages into your drawings and your construction schedule from the outset.
- Design-assist and detailing (1-2 weeks): the build-up, hardware and interfaces are validated against buildability, and shop drawings are produced for your approval. Catching a detailing clash here is essentially free; catching it on site is not.
- Submittals and approval (1 week): samples, coating and IGU data sheets, structural calculations and shop drawings are issued for approval, with clear hold points before anything is cut.
- Fabrication and processing (2-4 weeks): toughening, coating, DGU assembly and laminating. Coated and imported low-E substrates carry longer lead times, so release these first.
- Delivery and installation (project-dependent): sequenced with the frame and adjacent trades. A pre-installation mock-up is worth insisting on for large or bespoke facades, because it converts a paper specification into something you can water-test and sign off.
Specifying a mock-up and hold points is not bureaucracy - on Hyderabad's larger commercial projects it is the cheapest insurance you can buy against a repeated defect running across an entire elevation.
Common mistakes to avoid in a glass specification
Most facade problems trace back to a handful of avoidable specification errors rather than exotic engineering failures. Guard against these before you issue.
- Fixing glass thickness before the wind calculation, then discovering the pane is under-strength at height or over a large span.
- Specifying SHGC in isolation and starving the interior of daylight, when a selective high-VLT coating plus external shading would have met both cooling and lighting goals.
- Quoting acoustic Rw for a single pane rather than the full IGU, so the delivered unit under-performs against the client's expectation.
- Leaving safety-glass class 'implied by location' instead of marking IS 2553 class on each impact and overhead panel.
- Detailing the glass beautifully but leaving the hardware generic, so a floor spring or edge clamp is value-engineered down to something that fails early.
- Ignoring interfaces - frame bite, slab edge, spandrel and adjacent trades - where the majority of real-world facade leaks and failures actually begin.
A specifier's checklist before you issue
Run this list before the drawings leave your office. If any line is blank, the specification is not yet ready to price, and the gap will be filled on site by whoever is cheapest.
- Every glazing type has a target U-value, SHGC, VLT and (where relevant) Rw, with tolerances.
- Wind pressure derived per IS 875 Part 3 / NBC 2016 and glass thickness sized to it, with a deflection limit stated.
- Safety-glass class per IS 2553 marked on all human-impact and overhead zones.
- Full IGU build-up, coating surface, cavity fill, spacer and sealant specified.
- Hardware named by range and finish: patch fittings, floor springs, locks, sliding gear and clamps sized to load.
- All interfaces (frame, slab, spandrel, adjacent trades) detailed, not assumed.
- Green-rating credits (IGBC / GRIHA / LEED) and ECBC compliance cross-checked against the specified numbers.
- Submittal and mock-up requirements stated with hold points before fabrication. Hakimi Aluminium and Glass provides design-assist, shop drawings, fabrication and installation for architects across Hyderabad, Secunderabad, Telangana and Andhra Pradesh if you want any of these validated before you issue.
