Tendering, specs & the supply chain
The cheapest facade bid is almost never the cheapest facade - and the gap between the two is hidden in the specification you wrote, the supply chain behind the price, and the warranty that may or may not survive the company that signed it.
Three bids land on the table. The lowest is 30% cheaper than the others - which usually means it is either a mistake, a different scope, or a company that will not be there when the warranty is called.
Procuring a facade is not buying a product off a shelf - it is commissioning a bespoke engineered system from a specialist contractor whose price depends on a supply chain you cannot see. The architect's drawings and the consultant's spec go out to tender; bids come back. And here is the trap that catches inexperienced clients: the lowest number is rarely comparing like with like. One bidder priced a thicker glass, another excluded the brackets, a third assumed a cheaper aluminium finish that will chalk in five years. In India, where the facade-contracting market spans world-class firms and one-truck fabricators, reading a bid - and writing the spec that makes bids comparable - is a core facade-engineering skill.
Performance or prescriptive - the spec decides who owns the risk
Performance specs say what to achieve and move risk to the contractor; prescriptive specs say what to build and keep it
Every facade specification sits somewhere on a spectrum between two poles.
A performance specification states what the facade must achieve - air <= 1.5 m3/hr.m2 at 300 Pa, no water to 600 Pa, deflection <= span/175, U-value and SHGC targets, a movement allowance - and leaves the contractor to design a system that meets it. Because the contractor designs it, the contractor warrants it: the performance risk sits with them. This is the modern default on serious facades precisely because it gives the warranty teeth.
A prescriptive specification states exactly what to build - this extrusion, this gasket, this glass make-up, this sealant - and the contractor simply executes it. Here the design risk stays with the consultant: if the prescribed detail leaks, that is the specifier's problem, not the contractor's.
Most real specs are a hybrid - performance-led for the system, prescriptive for the things the architect or client insists on (a named glass coating, a specific aluminium finish, a sealant brand). The key discipline: be deliberate about which clauses are which, because every prescriptive clause you write is a piece of risk you just took back from the contractor.
Performance spec = 'hit these numbers, you design it, you warrant it.' Prescriptive spec = 'build exactly this, I own whether it works.' Every prescriptive line moves risk back to you.
Behind the bid sits aluminium, glass, sealant and a system house - and the warranty is only as good as the chain
A facade contractor's price is assembled from a supply chain, and understanding it is how you read the bid. The major cost streams are: aluminium extrusions (often from a system house - a company like a profile-system supplier that licenses a tested system to fabricators); glass (float, processed into toughened/laminated/IGU by a glass processor); sealants and gaskets (structural silicone is its own warranted sub-system); and the contractor's own fabrication and installation labour. A genuine specialist either runs its own fabrication or works from a reputable system house's tested system; a weak bidder may be improvising a system without that pedigree.
The warranties stack and they have gaps. A typical project carries: a system warranty (10-25 years on the aluminium finish from the system house), a glass/IGU warranty (often 5-10 years against seal failure and fogging), a structural silicone warranty (from the sealant maker, conditional on tested adhesion), and a workmanship/weathertightness warranty from the contractor (often shorter). The honest warning: a warranty is only worth the solvency of the company giving it and the conditions attached. A 25-year finish warranty from a firm that goes under in year three, or one voided because the wrong cleaning chemical was used, is paper. Assess who stands behind each warranty, not just the headline years.
Normalise the scope, then compare - the headline price is the least useful number on the page
Bids are rarely comparable as submitted, so the first job is to normalise them. Build a comparison that strips each bid back to a common scope: same glass make-up, same finish, same brackets, same testing, same scope of works. Then the differences become visible.
Watch for the four classic tricks (rarely malicious - usually just scope drift): exclusions (the cheap bid quietly excluded the steel sub-frame, or the testing, or the maintenance access provisions); qualifications (the bidder priced a cheaper glass coating 'or equivalent', or a thinner aluminium); provisional sums (a vague allowance for an unresolved detail that will balloon later); and programme assumptions (a price valid only for an installation rate the site can't actually sustain). A bid 30% below the others is a question, not a bargain: it usually means a different scope, a missed risk, or a contractor buying the job to survive - any of which becomes a variation claim later.
The real evaluation weighs price against capability: the bidder's track record on similar facades, their financial stability (will they outlast the warranty?), their proposed system's pedigree, their willingness to commit to the mock-up and testing regime, and the credibility of their programme. The cheapest compliant bid from a capable contractor wins - not simply the lowest number.
Your prescriptive insistences cost real money and move risk. If you name a specific glass coating or aluminium finish for a good aesthetic reason, write it as a clear prescriptive clause and accept that you have taken that decision's risk back from the contractor - don't bury it in a performance spec and then be surprised when the contractor substitutes. At bid stage, resist the gravitational pull of the lowest number: the firm that lowballs to win is the firm most likely to value-engineer your facade in the shop drawings and chase variations later. Protect your design by helping pick a capable contractor, not just a cheap one.
Write the spec so bids are comparable - a clear performance basis, a defined glass and finish basis-of-design, a mandated testing regime, and an explicit scope-of-works schedule that exclusions can be checked against. At tender, normalise every bid to a common scope before you compare a single rupee, and interrogate qualifications and provisional sums. Prequalify bidders on capability and financial stability - a warranty from an insolvent firm is worthless. And keep the performance/prescriptive boundary deliberate: each prescriptive clause is risk you have chosen to own, so own it knowingly.
On site you live with the contractor the tender chose, so it pays to know what a good one looks like: a credible system from a reputable system house, real fabrication capability, a programme they can actually hold, and the warranties documented and registered (many warranties require registration and correct maintenance to stay valid). When materials arrive, check they match the specified and tendered basis - the glass make-up, the aluminium finish, the sealant brand. A substitution that slipped through tender often shows up first as the wrong sticker on a crate. Catching it then is far cheaper than discovering it when the warranty is called.
CWCT Standard (UK)
Performance specification basis
The de-facto international basis for performance-led facade specs and the test regime they call up; common on Indian premium tenders. But citing CWCT is not a spec - the project must set the actual performance numbers, scope and testing it requires.
Eco-Niwas Samhita 2018 / ECBC 2017 (India)
Mandatory envelope performance in the spec
The Indian residential (ENS) and commercial (ECBC) envelope codes set the U-value, SHGC, RETV and VLT targets your performance spec must include - these are not optional 'nice-to-haves', they are code compliance the bid must price for.
NBC 2016 + IS 16231 (India)
Code and fenestration baseline
NBC 2016 frames the regulatory envelope and IS 16231 sets Indian fenestration performance the spec can call up - but the Indian facade-system warranty and contracting framework is less codified than the UK/Middle East, so contract and warranty terms carry more weight as of 2026.
“Pick the lowest compliant bid - that is what tendering is for, and it saves the client the most money.”
The lowest bid is the most expensive one to evaluate, because it is rarely comparing like with like. Facade bids differ in scope, glass and finish basis, exclusions, qualifications and programme assumptions, and a price 30% below the field almost always means a different scope, a missed risk, or a contractor lowballing to survive - all of which return as variation claims and value-engineering later. The cheapest facade over its life is the cheapest compliant bid from a capable, solvent contractor whose warranty will still exist when you need it - which is a different number from the lowest one on the page.
Worked example - normalise three facade bids and pick a winner
The core facade-procurement skill is normalising bids to a common scope before comparing price. Let's evaluate three bids for a 4,000 m2 curtain wall, the way a facade consultant builds a bid-comparison table.
The three bids, the tender spec's basis-of-design (glass, finish, testing, scope), and a simple comparison table.
GIVEN - three bids for a 4,000 m2 unitized curtain wall (spec basis: 6-12-6 low-E IGU, PVDF finish, full PMU + site testing, steel sub-frame included):
BID A : Rs 18,000 / m2 total Rs 7.20 cr - compliant, all scope included
BID B : Rs 14,500 / m2 total Rs 5.80 cr - EXCLUDES steel sub-frame (Rs 1,200/m2),
EXCLUDES PMU testing (Rs 0.25 cr),
glass 'or equivalent' single-silver low-E
BID C : Rs 17,200 / m2 total Rs 6.88 cr - compliant, PMU included,
provisional sum Rs 0.30 cr for corner detail- 1Establish the common scope. Every bid must be brought to the spec basis: full IGU make-up, PVDF finish, steel sub-frame, full PMU and site testing, corner detail resolved. Write these as the columns of your table - any bid missing a column is not yet comparable.
- 2Add back Bid B's exclusions. Bid B excluded the steel sub-frame (4,000 m2 x Rs 1,200/m2 = Rs 0.48 cr) and the PMU testing (Rs 0.25 cr). Add both: 5.80 + 0.48 + 0.25 = Rs 6.53 cr normalised. Its headline 'cheapest' Rs 5.80 cr was a different, smaller scope.
- 3Adjust Bid B for the glass qualification. Bid B priced a single-silver low-E 'or equivalent' against the spec's higher-spec coating - a performance downgrade (worse SHGC). To match spec, add an estimated Rs 300/m2 x 4,000 = Rs 0.12 cr: Rs 6.65 cr. Now Bid B is no longer the cheapest - and you have exposed a hidden performance compromise.
- 4Resolve Bid C's provisional sum. Bid C carried Rs 0.30 cr provisional for the corner detail. A provisional sum is a guess that can move either way; flag it as a risk and ask the bidder to firm it up before award rather than treating Rs 6.88 cr as fixed.
- 5Compare normalised prices. Bid A Rs 7.20 cr (firm, full scope), Bid B ~Rs 6.65 cr (was 'cheapest' at 5.80 but only after stripping scope), Bid C Rs 6.88 cr (firm bar one provisional). The real spread is far narrower than the headline numbers suggested - and Bid B's apparent saving was mostly missing scope.
- 6Weigh price against capability. Now overlay track record, financial stability and system pedigree. If Bid C's contractor has a stronger record on similar facades and a sounder system house, the ~Rs 0.23 cr difference over Bid B's normalised price may be the cheapest insurance on the project. Award the cheapest compliant bid from a capable, solvent contractor - here, likely Bid C, not the headline-cheapest Bid B.
You’ll walk away with
A normalised bid-comparison table that converts three non-comparable headline prices (Rs 5.80 / 6.88 / 7.20 cr) into like-for-like scope (~Rs 6.65 / 6.88 / 7.20 cr) and a defensible award recommendation - the single document that stops a client buying a 'cheap' facade that is really a different, riskier one.
Two ways to sharpen the procurement eye.
- 01Take any facade or fenestration quote you can find and hunt for the exclusions and qualifications - the 'excludes', 'by others', 'provisional' and 'or equivalent' lines. Those words are where the real price lives.
- 02Pick a named facade system house and a named glass processor and trace the supply chain for one curtain-wall panel: who makes the aluminium, who makes the glass, who fabricates, who installs, and who warrants each part?
A facade is procured, not bought: the specification decides whether the contractor owns the performance risk (performance spec, warranted) or you do (prescriptive spec), and every prescriptive clause moves risk back to you. Behind each bid sits a supply chain of aluminium, glass and sealant and a stack of warranties only as good as the firms behind them. Reading a bid means normalising scope first, then weighing price against capability - because the lowest number is the least useful one on the page.
Performance specs say what to achieve (contractor designs and warrants); prescriptive specs say what to build (specifier owns the risk); most specs are hybrid - be deliberate about which clauses are which. Behind the bid: aluminium (system house), glass (processor), sealant, fabrication/install, each with stacked warranties only as good as the firm's solvency and the conditions attached. To assess a bid: normalise to common scope, strip out exclusions/qualifications/provisional sums, then weigh price against capability and stability. Cheapest compliant bid from a capable, solvent contractor wins.
What is the difference between a performance and a prescriptive facade specification?
A performance specification states what the facade must achieve - air, water, wind, thermal, movement targets - and lets the specialist contractor design a system that meets them, so the contractor warrants the performance and carries the risk. A prescriptive specification states exactly what to build - specific profiles, gaskets, glass and sealants - and the contractor simply executes it, leaving the design risk with the specifier. Most real specs are hybrid, and the discipline is being deliberate about which clauses are which, because every prescriptive clause moves risk back from the contractor to you.
How do you assess a facade bid?
Normalise the bids to a common scope before comparing price - bring every bid to the same glass make-up, finish, sub-frame, testing and scope of works, and add back any exclusions, qualifications, provisional sums or programme assumptions. Then weigh the normalised price against the contractor's capability: track record on similar facades, financial stability (will they outlast the warranty?), system pedigree and commitment to the testing regime. The winner is the cheapest compliant bid from a capable, solvent contractor - which is often not the lowest headline number, because that one is usually a different, riskier scope.
What warranties come with a facade, and are they reliable?
A facade typically carries a stack: a system warranty on the aluminium finish (often 10-25 years from the system house), a glass/IGU warranty against seal failure and fogging (often 5-10 years), a structural silicone warranty from the sealant maker (conditional on tested adhesion), and a shorter workmanship/weathertightness warranty from the contractor. Their reliability depends on the solvency of the company giving each one and the conditions attached - many are voided by incorrect maintenance or cleaning, or require registration. A long warranty from a firm that may not exist in five years, or one easily voided, is worth little, so assess who stands behind each warranty, not just the headline years.
Peer-reviewed journals & authoritative standards
- 01Material Selection and Characterization for a Novel Frame-Integrated Curtain Wall. (PMC8069006). — Materials / NCBI-PMC, 2021.
- 02Su, Z. et al. Multi-Disciplinary Characteristics of Double-Skin Facades for Computational Modeling Perspective and Practical Design Considerations. Buildings, 12(10):1576. — Buildings (MDPI), 2022.
- 03Ventilated facade system: A review (system families, supply chain and practical design considerations). — ScienceDirect (Elsevier), 2025.
The tender chooses the contractor and the warranty; the mock-up proves the design. The last act is the riskiest: turning all of it into a skin actually hung on the building - the survey, the setting-out, the brackets that reconcile a rough frame to a precise facade, and the quality control that holds the installed skin to the tested one.