Plain definitions of the terms that appear on drawings, BOQs and tender documents — what each one means, how it is specified in India, and the mistakes that cost money on site.
Flanking is sound travelling between two spaces by any route other than straight through the wall between them — over the partition through the ceiling void, under it through a raised floor, along a duct, or through a junction. It is why a partition with a high laboratory rating often delivers far less in the finished building.
The fire rating of an aluminium composite panel is set almost entirely by what sits between its two aluminium skins: a standard polyethylene core burns readily, an FR (fire-retardant) core is mineral-filled to resist ignition, and an A2 core is mineral enough to be classed as limited-combustibility.
Air changes per hour is the number of times the full air volume of a space is replaced in one hour, calculated as supply airflow divided by room volume. It is a useful metric where the requirement relates to the room itself — dilution, contamination control, heat removal — and a poor one where the requirement relates to the people in it.
An air handling unit is a central assembly that filters, conditions and moves air to a group of spaces through ductwork. It typically contains filters, a cooling coil, a fan and dampers, and may handle outdoor air, return air or a mix. It serves many zones from one location, which concentrates both the plant and the maintenance.
Anodising grows a hard oxide layer out of the aluminium itself by electrolysis; powder coating sprays a polymer onto the surface and bakes it on. One is part of the metal, the other sits on top of it — which is why they age in completely different ways.
As-built drawings record what was actually installed, including every change made during construction, as distinct from the design drawings that showed what was intended. For concealed services in particular they are the only record of where things are, which makes them the most valuable document in a handover pack.
Busbar trunking is a prefabricated enclosure containing solid conductors, used to distribute power along a route with tap-off points at intervals. It replaces large cable bundles in rising mains and heavy horizontal distribution, and its tap-offs let loads be added or moved later without rewiring the run.
Cable derating is the reduction applied to a cable's tabulated current-carrying capacity to account for the conditions it is actually installed in — how many cables are bunched together, the ambient temperature, and the installation method. The tabulated figure assumes reference conditions that rarely exist on a real project.
Carpet area is the usable floor you can actually lay carpet on; built-up area adds the walls; super built-up (or chargeable) area adds a share of lobbies, lifts, staircases and services. Rent is usually quoted on super built-up, while fit-out is priced on carpet — which is why the two numbers must never be mixed up.
Cat 6 and Cat 6A are categories of twisted-pair network cable. Cat 6 is specified to 250 MHz and supports 10 Gbps only over shorter runs, around 55 metres; Cat 6A is specified to 500 MHz and supports 10 Gbps over the full 100-metre channel.
Cat A is the landlord's base finish — a blank, serviced but unusable floor with ceiling, lighting, basic HVAC and raised floor. Cat B is the tenant's build on top of it: the layout, cabins, meeting rooms, branding and everything that makes the space specific to one occupier.
A chilled beam is a ceiling unit that cools a room by passing chilled water through a coil, with no fan of its own. Passive beams cool by natural convection; active beams use the building's fresh air supply to draw room air across the coil. Because the coil runs above the room's dew point, the beam handles sensible heat only, so humidity must be controlled separately.
Commissioning is the process of proving that installed systems work as designed — individually and together — and recording the evidence. It goes beyond testing that equipment switches on: it covers balancing, control response, interfaces between systems and performance against the design intent.
Curing is keeping freshly placed concrete moist and at a suitable temperature long enough for the cement to hydrate and gain strength. Concrete that dries out early stops hydrating, and ends up weaker, more permeable and more prone to cracking than its mix design intended.
Condensate drainage removes the water that forms continuously on a cooling coil when air is cooled below its dew point. Because the coil sits under negative or positive pressure, the drain needs a correctly sized trap as well as continuous fall — without both, water backs up into the tray and appears as a stain in the ceiling below.
A construction tolerance is the permitted difference between the size or position shown on a drawing and what is actually built. Every trade works to its own tolerance: in-situ concrete is less precise than factory-made steel, aluminium or glass. Where trades meet, the design must provide enough adjustment to absorb the difference.
Curtain wall brackets are the steel or aluminium anchors that connect the facade to the building's slab edges. They carry the facade's weight and wind load into the structure, and they are adjustable in three directions so the facade can be set true against a structure that is never perfectly built.
Daylight factor is the ratio of indoor daylight illuminance at a point to the outdoor illuminance under an overcast sky, expressed as a percentage. It describes how much of the available daylight reaches a given position, so it falls sharply as you move away from a window and is a useful way to judge how deep a floor plate can usefully be daylit.
The defects liability period is a stated time after practical completion during which the contractor must return and make good defects that appear in their work. It is not a maintenance agreement and not a warranty on everything in the building — it covers defects arising from the contractor's work, not wear, misuse or items with their own manufacturer warranty.
Demountable partitions are prefabricated wall systems — solid, glazed or mixed panels on a proprietary frame — designed to be taken down and reinstalled elsewhere rather than demolished. They trade a higher initial cost for the ability to reconfigure an office with little waste.
A double glazed unit is two panes of glass separated by a sealed, dried air or argon cavity held apart by a spacer bar. The cavity is what insulates; the edge seal is what keeps the cavity dry, and when that seal fails the unit fogs permanently.
Earthing provides a deliberate low-impedance path to earth so that a fault current is large enough to operate the protective device quickly. Bonding connects exposed and extraneous metalwork together so that, during a fault, everything a person can touch simultaneously stays at a similar potential. They are complementary and neither substitutes for the other.
A facade mock-up is a full-size sample of the actual system — real profiles, real glass, real seals — built and tested before the facade goes into production, so that appearance and performance are proven on a few square metres rather than discovered across the whole building.
A fan coil unit is a small terminal unit containing a fan, a coil fed with chilled or hot water, and a filter. It conditions the air of the space it serves without providing outdoor air, so a separate fresh air supply is required. FCUs give room-level control and are typically concealed above ceilings.
A fire NOC is the no-objection certificate a state or city fire service issues to confirm a building's fire safety provisions meet the applicable requirements. Buildings above certain heights, areas or occupancy thresholds need it — typically a provisional clearance at design stage and a final one before occupation.
Fire-rated glass is glazing tested to keep a fire compartment intact for a stated time. An integrity (E) rating means it stops flames and smoke passing; an insulation (EI) rating also limits the heat transmitted to the protected side, so people can pass close to it during a fire.
A gypsum ceiling is a continuous surface of plasterboard fixed to a metal frame, jointed and painted to look seamless. A mineral fibre ceiling is a grid of removable tiles in a suspended metal frame. Gypsum gives a clean finish; mineral fibre gives access to the services above.
Harmonic distortion is the change in the shape of the supply current or voltage caused by loads that draw current in pulses rather than as a smooth wave. Electronic equipment such as LED drivers, computers, UPS systems and variable speed drives does this. The result is extra current at multiples of the supply frequency, measured as total harmonic distortion (THD).
Heat soak testing holds toughened glass at an elevated temperature for a set period after toughening, so panes containing nickel sulphide inclusions break in the factory instead of on the building. It reduces, though does not eliminate, the risk of toughened glass shattering spontaneously in service.
An HT (high-tension) panel receives the utility's high-voltage supply — commonly 11kV — and protects and switches it before the transformer. An LT (low-tension) panel takes the transformer's low-voltage output, typically 415V, and distributes it across the building to sub-distribution boards.
Interstitial condensation is water that forms inside a wall, roof or floor build-up when water vapour moving through it meets a layer colder than its dew point. It is hidden, so it is usually found only after insulation has lost performance, metal has corroded or mould has appeared.
An IP rating states how well an enclosure resists ingress, using two digits: the first for solid objects and dust, the second for water. IP65, for example, is dust-tight and protected against water jets. The digits describe tested resistance to specific conditions, not general robustness.
Toughened glass is heat-treated to be several times stronger than ordinary glass and breaks into small, blunt granules. Laminated glass bonds two or more panes with a plastic interlayer, so when it breaks the fragments stay stuck to the interlayer and the pane stays in place.
Lighting power density (LPD) is the installed lighting load divided by floor area, in watts per square metre. Energy codes such as ECBC 2017 set maximum LPD values by building type, so the lighting design has to hit its lux targets within a power budget.
Low-E — low-emissivity — glass carries a microscopically thin metallic coating that reflects heat radiation while letting visible light through. It reduces heat transfer through the glass, and solar-control variants also cut the sun's heat gain — which is what matters most in hot Indian climates.
Lux is illuminance — the amount of light falling on a surface, measured in lumens per square metre. It is the headline figure in any lighting specification, and on its own it describes almost nothing about whether a space is comfortable to work in.
A movement joint is a deliberate gap that lets parts of a building expand, contract or shift relative to each other without stressing the material between them. Movement happens regardless; the joint decides whether it is accommodated in a designed location or released as a crack somewhere unplanned.
Mullions are the vertical members of a curtain wall and transoms are the horizontal members that span between them. Mullions carry wind and self-weight back to the building's slabs through brackets; transoms carry the glass weight to the mullions and divide the facade into panels, and their joints are where most of the drainage design happens.
NRC — Noise Reduction Coefficient — is a single number between 0 and 1 describing how much sound a surface absorbs rather than reflects. An NRC of 0.70 means the material absorbs roughly 70% of the sound striking it, averaged across the speech-frequency range.
Plenum depth is the clear vertical space between the structural soffit above and the top of the suspended ceiling below. Every service that crosses the floor — ducts, sprinkler pipework, cable containment, lighting, structural downstands — has to fit inside it, which is why it governs the finished ceiling height an occupier actually gets.
Power factor is the ratio of the power that does useful work to the total power drawn from the supply. Motors, transformers and some electronics draw extra reactive current, which lowers it. Power factor correction adds capacitors, usually in an automatic (APFC) panel, to supply that reactive current locally, so less current is drawn from the grid.
Practical completion is the point at which the works are complete enough for the client to take possession and use them for their intended purpose, even if minor items remain. It is a contractual milestone rather than a description of a finished building, and it starts the defects liability period.
Pressure equalisation keeps water out of a facade by allowing air into the cavity behind the outer skin, so the pressure inside roughly matches the pressure outside. With no pressure difference across the joint, wind has nothing to push water through, even though the outer surface is not sealed.
Purlins are the horizontal members spanning between roof frames that carry the roof sheeting; girts are their equivalent on the walls, carrying wall cladding. Together they are the secondary framing that transfers cladding loads into the main frames.
A raft foundation is a single thick reinforced slab spreading the building's load across the whole footprint on soil near the surface. A pile foundation carries load down through long columns into deeper, stronger strata. Which one a building needs depends on the soil and the loads.
A rainscreen ventilated facade hangs an outer skin of panels in front of an insulated, weatherproofed wall with a deliberate air gap between them. The outer panel sheds most of the rain; the drained and ventilated cavity behind handles whatever gets past it.
A raised access floor is a grid of removable panels sitting on adjustable pedestals above the structural slab, creating a shallow service void for power, data and sometimes air — so cabling can be rerouted later by lifting a tile rather than opening a ceiling.
An MCB protects the circuit and the cable by disconnecting on overload or short circuit. An RCCB protects people by detecting current leaking to earth — for example through a person — and disconnecting quickly. They respond to entirely different events, so neither replaces the other, and an RCBO combines both functions in one device.
Reverberation time is how long a sound takes to decay by 60 decibels after its source stops, commonly written RT60. It is governed by room volume and the amount of absorption in the room, so a large hard-finished space rings and the same space with absorbent surfaces sounds controlled.
Sanctioned load is the maximum electrical load the distribution company has approved a premises to draw, in kW or kVA. It is applied for based on the building's connected load with diversity applied, and it sets the supply type, the fixed charges and whether the connection is LT or HT.
A screed is the layer laid over a structural slab to produce a level, sound surface for the floor finish, and to carry services or insulation where required. It is hidden once the finish goes down, but its flatness, strength and dryness largely determine whether that finish performs or fails.
Solar Heat Gain Coefficient is the fraction of solar radiation striking a glazed unit that ends up as heat inside the building — an SHGC of 0.25 means a quarter of the sun's energy gets through. In a hot climate it is the single most important number on a glass specification.
A silicone weatherseal is the flexible sealant bead between glass, panels or frames on the outside of a facade. Its job is to keep water and air out while the joint opens and closes with temperature and building movement. It carries no structural load, which is what separates it from structural silicone.
A slab edge firestop is the fire-resistant seal in the gap between the back of a curtain wall and the edge of each floor slab. Without it that continuous perimeter gap is an open vertical route for fire and smoke between floors, bypassing the floor's own fire resistance entirely.
Snagging is the inspection that identifies incomplete or below-standard finishing work before handover, recorded as a list the contractor must close out. It is about workmanship and finish — not about system performance, which is commissioning, and not about latent faults appearing later, which is the defects liability period.
Spandrel glass is the opaque glazing used to conceal the floor slab, ceiling void and services between one floor's vision glass and the next, so a facade reads as continuous glass from outside.
Spider glazing supports glass on stainless-steel arms — spiders — bolted through holes drilled in the panel corners, so the glass is carried at points rather than along its edges. Removing the frame is what makes an atrium or lobby read as glass with almost nothing holding it up.
Sprinkler hazard classification groups occupancies by how quickly and intensely a fire in them is likely to develop — broadly light, ordinary and high hazard — and that class sets the water density, the area of operation, and therefore the pump and tank size the system needs.
The static regain method sizes a supply duct so that, after each branch takes off, the drop in air velocity converts some velocity pressure back into static pressure. Sized correctly, that regained pressure offsets the friction lost along the next section, so the static pressure is roughly the same at every outlet and the system needs less balancing.
STC (Sound Transmission Class) is a single-number rating of how well a wall, door or glazing stops airborne sound passing from one room to the next. A higher number means better insulation. The international equivalent is Rw. Both are measured in a laboratory, so they describe the element, not the finished room.
Stick system glazing is a curtain wall assembled on site from individual components: vertical mullions fixed back to the structure, horizontal transoms between them, and glass or panel infill installed into the resulting grid. It is the traditional and most flexible form of curtain walling, well suited to low and medium rise and to irregular geometry.
Structural silicone glazing uses a load-bearing silicone sealant to bond glass directly to its supporting frame, so wind load transfers through the adhesive rather than through mechanical clamps — which is what allows a facade to read as flush glass with no visible framing outside.
A tapered frame is the primary portal frame of a pre-engineered building, built from welded plate sections whose depth varies along their length — deep where bending moment is highest, such as at the knee and ridge, and shallow where it is low — so steel is placed only where the load needs it.
A thermal break is an insulating strip — usually polyamide — bonded between the inner and outer halves of an aluminium profile, so heat cannot conduct straight through the frame. Without it, the frame is a continuous metal bridge between outside and inside.
U-value, or thermal transmittance, is the rate at which heat passes through a building element per unit area for each degree of temperature difference across it. Lower is better insulated. It is the inverse of R-value, and it describes conducted heat only — not the solar radiation passing through glass, which is measured separately as SHGC.
A unitized curtain wall is a glazed facade delivered as complete factory-assembled panels — glass already set into its frame — which are lifted into place and locked to the building floor by floor, rather than being built up from separate components on site.
A VAV — variable air volume — system cools different zones by varying how much conditioned air each receives, through motorised VAV boxes in the ductwork controlled by zone thermostats. Rooms that need less cooling get less air, rather than everything getting the same airflow.
Visible light transmission is the fraction of visible daylight that passes through a glazing unit, expressed as a percentage or decimal. It governs how bright the interior is and how much daylight reaches into the floor plate, and it usually falls as solar control improves — which is the trade-off at the centre of glass selection.
A wet riser is a vertical pipe permanently filled with pressurised water, running up a building with landing valves at each floor, so firefighters can connect hoses on the fire floor instead of laying them up the stairs. It is fed from the building's fire pumps and tank.
Workstation density is the usable office area allocated per person, usually expressed in square feet of carpet area per seat. It includes each person's share of circulation, meeting rooms and support spaces, not just the desk they sit at.
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