Intermediate Architectural & Building Engineering interview questions

150 questions with answers (ARC-151 to ARC-300). Try each one aloud before reading the answer.

Architectural Design Principles

ARC-151 · How does a courtyard plan help in hot climates?

The courtyard is shaded by surrounding walls for much of the day and collects cool night air, which then flows into rooms. It also drives stack and cross ventilation and brings daylight to inner rooms. Water and plants add evaporative cooling.

ARC-152 · How are stair risers and treads proportioned?

A comfortable stair follows 2R + T ≈ 600–630 mm, where R is riser and T is tread. NBC 2016 limits residential risers to 190 mm with treads of at least 250 mm. Public buildings need lower risers and wider treads.

ARC-153 · What is the maximum ramp gradient for wheelchair access and why?

Generally 1:12, with level landings at intervals and handrails on both sides. Steeper ramps need more effort to climb and are unsafe to descend. Gentler slopes such as 1:15 or 1:20 are preferred for long runs.

ARC-154 · What is floor-plate efficiency?

The ratio of net usable or lettable area to gross floor area, as a percentage. Cores, shafts, corridors and wall thickness reduce it. Office towers typically aim for about 75–85%.

ARC-155 · What is modular coordination?

Sizing buildings and components in multiples of a basic module, M = 100 mm, so that standard components fit together without cutting. It cuts waste, simplifies design and supports prefabrication.

ARC-156 · How is a structural grid chosen for an office building with basement parking?

The grid must suit both office planning and parking below. Spans of about 8–9 m fit three car bays between columns and give flexible open-plan offices. Larger spans need deeper beams or post-tensioning, which affects floor height.

ARC-157 · How does plan depth affect daylight and natural ventilation?

Daylight reaches usefully to about 2 to 2.5 times the window head height from the façade. Single-sided ventilation works to about 2.5 times the ceiling height. Cross-ventilation works to about 5 times. Deeper plans need atria, light wells or mechanical systems.

ARC-158 · What is a design brief or programme?

A document that sets the client's requirements: spaces, areas, adjacencies, users, budget, schedule, performance targets and constraints. It is the reference against which designs are developed and checked.

ARC-159 · What is a figure-ground diagram?

A plan drawing showing built mass in black and open space in white. It reveals urban grain, street pattern, density and how a new building relates to its context.

ARC-160 · Why are hierarchy and axis used in architectural composition?

An axis is a line that organises spaces and gives direction and symmetry. Hierarchy gives important spaces greater size, height, unique shape or a central position. Together they make a building legible and show its main functions.

ARC-161 · How is corridor width decided?

By occupant load and egress capacity under fire codes, the movement of trolleys, beds or wheelchairs, and the corridor's length. Hospitals need wide corridors for bed movement. Offices and housing need less, but never less than the code minimum.

ARC-162 · What is contextual design?

Design that responds to its surroundings: climate, topography, street pattern, neighbouring building heights, materials, culture and history. It aims for buildings that fit their place rather than impose an unrelated form.

ARC-163 · What is the difference between symmetry and balance in design?

Symmetry is a mirror arrangement of elements about an axis. It gives formality and stability. Balance is visual equilibrium, which can be achieved asymmetrically by offsetting different masses, colours or textures.

Building Materials

ARC-164 · What is a U-value and how is it calculated?

Thermal transmittance, the heat flow per m² per kelvin of temperature difference across an element, in W/m²K. U = 1/(Rsi + Σ d/k + Rso), adding air-film and layer resistances. A lower U-value means better insulation.

ARC-165 · What is the thermal resistance of a material layer?

R = d/k, in m²K/W, where d is thickness in metres and k is thermal conductivity in W/m·K. For example, 50 mm of insulation with k = 0.035 gives R = 0.05/0.035 ≈ 1.43 m²K/W.

ARC-166 · What causes efflorescence on masonry?

Soluble salts in bricks, mortar or soil dissolve in water that moves through the wall. When the water evaporates at the surface, the salts crystallise as a white deposit. Controlling moisture and using low-salt materials prevent it.

ARC-167 · Why is fly ash added to concrete?

Fly ash reacts with calcium hydroxide released by cement hydration to form extra binding gel. This improves workability, long-term strength and durability, and lowers heat of hydration, cost and embodied carbon. Early strength gain is slower.

ARC-168 · What are the main types of chemical admixtures in concrete?

Plasticisers and superplasticisers raise workability or cut water. Retarders delay setting for hot weather or long hauls. Accelerators speed early strength. Air-entraining agents give freeze–thaw resistance. Waterproofing admixtures reduce permeability.

ARC-169 · What are SHGC and VLT for glazing?

The solar heat gain coefficient (SHGC) is the fraction of incident solar radiation that enters through the glazing as heat. Visible light transmittance (VLT) is the fraction of visible light that passes through. Hot climates want low SHGC with reasonably high VLT.

ARC-170 · What is low-emissivity (low-E) glass?

Glass with a thin metallic oxide coating that reflects long-wave infrared. It reduces radiant heat transfer and lowers the U-value. Spectrally selective low-E coatings also cut solar heat gain while passing most visible light.

ARC-171 · How does a double-glazed unit improve thermal performance?

Two panes are separated by a sealed gap filled with dry air or argon. The gap adds thermal resistance, cutting the U-value from about 5.8 W/m²K for single clear glass to about 2.8 W/m²K. Low-E coatings and argon reduce it further.

ARC-172 · Why does structural steel need fire protection?

Steel conducts heat quickly and loses strength and stiffness as it heats, retaining only about half its room-temperature strength at around 550–600 °C. Intumescent paint, boards or sprayed coatings slow heating to meet the required fire rating.

ARC-173 · What are CLT, glulam and LVL?

Engineered timber products. Cross-laminated timber (CLT) is panels of layers glued at right angles, used for walls and floors. Glulam is laminations glued parallel to make beams and columns. LVL is veneers glued parallel, for strong straight members.

ARC-174 · What are compressed stabilised earth blocks (CSEB)?

Blocks made of soil mixed with a small amount of cement or lime, compressed in a press and cured. They have low embodied energy, use local soil and give good thermal mass, but need protection from erosion.

ARC-175 · What causes cracking in concrete?

Plastic shrinkage from rapid surface drying, drying shrinkage, thermal contraction, settlement, overloading, and reinforcement corrosion. Good mix design, proper curing, adequate cover, joints and reinforcement control it.

ARC-176 · Why is concrete cover to reinforcement important?

Cover protects steel from corrosion by keeping carbonation and chlorides away. It gives fire resistance and ensures bond. IS 456 sets minimum nominal cover by exposure condition, from mild to extreme.

Building Construction Techniques

ARC-177 · What is aluminium formwork (Mivan) construction?

A system of lightweight aluminium panels that forms walls and slabs together. They are cast monolithically in a fast cycle, about one floor every few days. It suits repetitive mass housing and gives good surface finish but needs early, frozen design.

ARC-178 · What is slipform construction?

Continuous casting of tall vertical structures such as cores, silos and chimneys. A form is jacked upward slowly while concrete is placed, so the concrete sets as the form rises. It is fast but needs round-the-clock work.

ARC-179 · What is a pre-engineered building (PEB)?

A steel building system with tapered built-up frames, cold-formed purlins and girts, and metal cladding. It is designed and fabricated in a factory and bolted on site. It suits warehouses and factories with fast build and long clear spans.

ARC-180 · What is the difference between construction, expansion and contraction joints?

A construction joint is where concreting stops and restarts, located at points of low shear. A contraction joint is a planned weakness that controls shrinkage cracking. An expansion joint is a full gap separating blocks to allow movement.

ARC-181 · Why does plaster crack at RC frame and masonry junctions, and how is it prevented?

Concrete and masonry have different shrinkage, thermal and elastic movement, so the joint opens. Fixing galvanised mesh across the junction before plastering, or forming a groove, controls the cracking.

ARC-182 · What is the difference between stick and unitised curtain walls?

A stick system is assembled on site from mullions, transoms and glass, piece by piece. A unitised system is factory-made in storey-high panels that are craned and hung. Unitised gives faster installation and better quality, but costs more and needs more planning.

ARC-183 · What is top-down construction?

Building basement floors from the top downward after perimeter walls and piles are installed. Each slab braces the walls as excavation continues below, while the superstructure can rise at the same time. It suits deep basements in congested city sites.

ARC-184 · How are basements waterproofed?

By external tanking membranes, crystalline or integral waterproofing in dense concrete, water bars at joints, internal cavity drain systems, and dewatering or drainage. The chosen grade depends on how dry the space must be.

ARC-185 · Why are flat roofs given a slope?

To drain rainwater quickly to outlets and avoid ponding, which causes leakage and extra load. A fall of about 1 in 100 or more is commonly given using screed or tapered insulation.

ARC-186 · What is light gauge steel framing (LGSF)?

Building frames of cold-formed galvanised steel sections, screwed or bolted together and clad with boards. It is light, quick, precise and recyclable, and suits low-rise housing, extensions and infill walls.

ARC-187 · What is 3D concrete printing in construction?

Extruding a special printable cementitious mix layer by layer from a robotic arm or gantry to build walls directly from a digital model. It reduces formwork and labour and allows free forms. Reinforcement and code acceptance are still challenges.

ARC-188 · What is a raised access floor?

A floor of removable panels on adjustable pedestals over the structural slab. The void carries cables, data and sometimes underfloor air distribution. It is used in offices and data centres for flexibility.

ARC-189 · What are the main stages of a building's construction sequence?

Site preparation and setting out, excavation, foundations, plinth and DPC, superstructure frame and slabs, masonry, roofing and waterproofing, services first fix, plaster and flooring, doors and windows, services second fix, finishes, testing and handover.

Structural Systems for Buildings

ARC-190 · What is the difference between a moment-resisting frame and a braced frame?

A moment frame resists lateral loads by bending in rigid beam–column joints, which keeps the plan open but allows more sway. A braced frame uses diagonal members that act in axial force. It is stiffer and lighter but obstructs openings.

ARC-191 · What is a tube structure in tall buildings?

A system where closely spaced perimeter columns and deep spandrel beams act like a hollow cantilever tube fixed at the ground. Framed, braced, tube-in-tube and bundled-tube variants allow very tall buildings efficiently.

ARC-192 · What are the advantages of post-tensioned slabs?

High-strength tendons are tensioned after the concrete hardens. They allow longer spans, thinner slabs, less deflection and cracking, and fewer columns. Floor-to-floor height falls. Care is needed with later openings and with tendon anchorages.

ARC-193 · What is a transfer girder and what is its drawback?

A deep beam or slab that picks up columns or walls from above and carries them onto a different column layout below, for example over a lobby. It is heavy, costly and creates a stiffness irregularity that performs poorly in earthquakes.

ARC-194 · What are the seismic zones of India under IS 1893 (Part 1):2016?

Four zones, II to V, with zone factors Z = 0.10, 0.16, 0.24 and 0.36. Zone V, covering the North-East, parts of the Himalaya and Kutch, is the most severe.

ARC-195 · What is the approximate natural period of an RC moment frame per IS 1893?

For an RC moment-resisting frame without masonry infill, Tₐ = 0.075 h^0.75 seconds, where h is height in metres. For a 30 m building, Tₐ ≈ 0.075 × 12.8 ≈ 0.96 s. Frames with infill use Tₐ = 0.09h/√d.

ARC-196 · What is the strong column–weak beam principle?

Columns are made stronger in flexure than the beams framing into them, so plastic hinges form in beams first during an earthquake. This avoids a storey mechanism where columns fail and the floor above collapses.

ARC-197 · Why are short columns dangerous in earthquakes?

A column restrained partly by a stiff element such as a partial-height wall, a mid-height beam or a sloping site has a short effective height. It attracts much higher shear and fails in brittle shear unless detailed for it.

ARC-198 · How is design wind pressure calculated under IS 875 (Part 3)?

Design wind speed Vz = Vb·k1·k2·k3·k4, where Vb is basic wind speed and the factors cover risk, terrain and height, topography and importance. Design wind pressure pz = 0.6 Vz², in N/m² with Vz in m/s.

ARC-199 · What are plan irregularities that worsen seismic response?

Torsional irregularity, re-entrant corners projecting more than about 15% of plan dimension, floor slab openings and discontinuities, out-of-plane offsets and non-parallel lateral systems. They cause torsion and stress concentration.

ARC-200 · What is the typical deflection limit for floors under IS 456?

Final deflection is limited to span/250. Deflection after partitions and finishes are built is limited to span/350 or 20 mm, whichever is less, to avoid cracking finishes.

ARC-201 · What is a composite steel deck floor?

Profiled steel decking acts as permanent formwork and tensile reinforcement for a concrete topping. Shear studs welded to steel beams make beam and slab act compositely, giving stiffer, lighter and faster floors.

Plumbing & Electrical Services

ARC-202 · What are fixture units in drainage and water-supply design?

A fixture unit is a relative load factor assigned to each sanitary fixture based on its flow rate, duration and frequency of use. Adding fixture units for a pipe and applying probability tables gives the design flow and pipe size.

ARC-203 · What is a hydropneumatic water supply system?

Pumps with pressure vessels supply water directly to fixtures at controlled pressure, replacing or reducing overhead tanks. Variable-speed pumps start and stop as pressure falls or rises. It gives uniform pressure and frees the roof.

ARC-204 · Why is pressure zoning needed in high-rise plumbing?

Static pressure rises by about 1 bar per 10 m of height. Lower floors would get excessive pressure, causing noise, splashing, leaks and fixture damage. Buildings are split into vertical zones fed by intermediate tanks, booster pumps or pressure-reducing valves.

ARC-205 · What is the difference between greywater and blackwater?

Greywater is wastewater from basins, showers and washing machines, which is lightly contaminated and can be treated for flushing and irrigation. Blackwater is from WCs and often kitchens. It contains faecal matter and needs full sewage treatment.

ARC-206 · What is water hammer and how is it prevented?

A pressure surge when flowing water is stopped suddenly, for example by a fast-closing valve, causing banging and possible pipe damage. It is prevented by slow-closing valves, lower velocities, air chambers or water-hammer arrestors.

ARC-207 · What is the difference between connected load, maximum demand and diversity factor?

Connected load is the sum of the ratings of all equipment. Maximum demand is the highest load actually drawn over a period. Diversity factor is the sum of individual maximum demands divided by the maximum demand of the whole system, which is at least 1. It lets supply be sized below connected load.

ARC-208 · Why is power factor correction used in buildings?

Inductive loads such as motors and transformers draw reactive power, which lowers the power factor. Capacitor banks supply reactive power locally. This reduces current, losses, kVA demand and utility penalties.

ARC-209 · What is the role of a DG set and an ATS?

A diesel generator provides standby power during mains failure. An automatic transfer switch detects mains loss, starts the generator and transfers essential loads. It switches back when mains returns, without paralleling the two sources.

ARC-210 · What are TN-S, TN-C-S and TT earthing systems?

In TN-S, the supply provides separate neutral and protective earth conductors. In TN-C-S, a combined PEN conductor splits into N and PE at the installation. In TT, the installation has its own earth electrode independent of the supply earth, so RCDs are essential.

ARC-211 · What are the main parts of a lightning protection system?

Air terminals or a mesh on the roof to intercept strikes, down conductors to carry current, an earth termination system to disperse it, and equipotential bonding with surge protective devices for internal systems. IEC 62305 governs design.

ARC-212 · Why is cable voltage drop limited?

Excess voltage drop makes motors run hot, lights dim and electronics malfunction. Cables are sized so drop from source to load stays within limits, commonly about 3–5%, as well as for current-carrying capacity and short-circuit rating.

ARC-213 · What is a sewage treatment plant (STP) in a building complex and why is it needed?

An on-site plant that treats sewage, often by aerobic biological processes such as MBBR or SBR, followed by filtration and disinfection. Treated water is reused for flushing, landscaping and cooling towers. Many authorities require STPs for large developments.

HVAC & Mechanical Services

ARC-214 · What is thermal comfort?

The condition of mind that expresses satisfaction with the thermal environment, as defined in ASHRAE 55. It depends on air temperature, mean radiant temperature, humidity and air speed, plus the occupant's clothing and metabolic rate.

ARC-215 · What are PMV and PPD?

Predicted Mean Vote (PMV) predicts the average thermal sensation of a large group on a scale from −3 (cold) to +3 (hot). Predicted Percentage Dissatisfied (PPD) is the share expected to be dissatisfied. PMV = 0 still gives a PPD of about 5%.

ARC-216 · What is the adaptive comfort model?

A model in which acceptable indoor temperatures in naturally ventilated buildings track the recent outdoor mean temperature, because people adapt by clothing, windows and fans. ASHRAE 55 includes it. India's IMAC model calibrates it for Indian conditions.

ARC-217 · What is the difference between chilled-water and DX systems?

DX (direct expansion) systems cool air directly with refrigerant in the indoor coil, as in split and VRF units. Chilled-water systems use a central chiller to cool water that is pumped to AHUs and FCUs. They suit large buildings with better efficiency and control.

ARC-218 · How is fresh-air ventilation calculated under ASHRAE 62.1?

The ventilation rate procedure adds a people component and an area component: Vbz = Rp·Pz + Ra·Az. For offices, Rp = 2.5 L/s per person and Ra = 0.3 L/s·m². For 20 people in 200 m², Vbz = 50 + 60 = 110 L/s.

ARC-219 · How do you calculate sensible cooling load for an air stream?

Q = ρ·cp·V·ΔT ≈ 1.2 × V(L/s) × ΔT (K) in watts. For 500 L/s cooled by 10 K, Q ≈ 1.2 × 500 × 10 = 6000 W, or 6 kW. In IP units, Q (BTU/h) ≈ 1.08 × CFM × ΔT (°F).

ARC-220 · What is demand-controlled ventilation?

Varying outdoor air supply with actual occupancy, usually sensed by CO₂ levels or occupancy counts. It cuts the energy to condition fresh air in spaces with variable occupancy, such as meeting rooms and auditoriums.

ARC-221 · What is an energy recovery ventilator?

A device that transfers heat, and in enthalpy wheels or membranes also moisture, between exhaust air and incoming fresh air. In hot-humid climates it precools and dehumidifies fresh air, cutting cooling load.

ARC-222 · What is the difference between VAV and CAV systems?

A constant air volume (CAV) system supplies fixed airflow and varies supply temperature. A variable air volume (VAV) system supplies air at a fixed temperature and varies airflow to each zone with terminal boxes. VAV saves fan energy at part load.

ARC-223 · What is an air-side economiser?

A control mode that uses more outdoor air for cooling when outdoor air is cooler or drier than return air. It reduces or stops chiller operation. ECBC and ASHRAE 90.1 require economisers for certain systems and climates.

ARC-224 · What is the difference between direct and indirect evaporative cooling?

Direct evaporative cooling evaporates water into the supply air, lowering temperature but raising humidity. Indirect cooling cools the air through a heat exchanger without adding moisture. Both work best in hot-dry climates.

ARC-225 · What are the main duct sizing methods?

Equal friction keeps a constant pressure drop per metre and is common for low-velocity supply ducts. Static regain sizes ducts so static pressure recovered after branches offsets losses. Velocity reduction steps down velocity along the run.

Fire Safety

ARC-226 · How is occupant load calculated for egress design?

Occupant load = floor area ÷ occupant load factor (m² per person). The factor comes from the code for each occupancy. Assembly areas have small factors, meaning dense occupancy; offices and storage have large ones. The result sizes exits, stairs and doors.

ARC-227 · How is the exit width calculated under NBC 2016?

Exit width is measured in units of 500 mm. Number of units = occupant load ÷ persons allowed per unit for that occupancy and exit type: stair, ramp or door. Required width = units × 500 mm, subject to the code minimum widths.

ARC-228 · Why is smoke control so important in building fires?

Most fire deaths are caused by smoke and toxic gases, not burns. Smoke also cuts visibility and blocks escape. Smoke extraction, pressurisation, smoke barriers and curtains keep escape routes tenable.

ARC-229 · What is a fire lift?

A lift that firefighters can take control of during a fire. It has a protected shaft and lobby, a secondary power supply, fire-resisting doors and a firefighter switch. It lets them reach upper floors quickly with equipment.

ARC-230 · What is fire load density?

The total calorific energy of combustible contents and construction in a compartment divided by its floor area, in MJ/m². It indicates potential fire severity and duration, and is used to set fire resistance and suppression requirements.

ARC-231 · What is the difference between passive and active fire protection?

Passive protection is built into the fabric and needs no activation: fire-rated walls, floors, doors, fire stopping and structural protection. Active protection operates during a fire: detectors, alarms, sprinklers, hydrants, smoke extraction and pressurisation.

ARC-232 · What is fire stopping?

Sealing gaps around pipes, cables and ducts where they pass through fire-rated walls and floors. Tested sealants, collars, pillows and mortars are used, so the compartment keeps its rated resistance to fire and smoke.

ARC-233 · What are the main types of sprinkler systems?

Wet pipe systems are always water-filled. Dry pipe systems have pressurised air and suit areas at risk of freezing. Pre-action systems need detection before water enters the pipes and suit sensitive areas. Deluge systems have open heads that all discharge at once, for high-hazard areas.

ARC-234 · Why are clean-agent gas systems used in server rooms?

Water would damage electronics. Clean agents such as HFC-227ea, FK-5-1-12 or inert gas mixtures put out fire by absorbing heat or reducing oxygen. They leave no residue, but need a sealed room and safety interlocks.

ARC-235 · What is the difference between conventional and addressable fire alarm systems?

A conventional system groups detectors into zones, so the panel shows only which zone is in alarm. An addressable system gives every device a unique address, so the panel pinpoints the exact device. This speeds response and helps maintenance.

ARC-236 · What does a fire damper do?

It is a device in ductwork where ducts cross fire-rated walls or floors. A fusible link or actuator closes it automatically during a fire, so fire cannot spread through the ducts and compartmentation is maintained.

ARC-237 · Why should ordinary lifts not be used during a fire?

Shafts can fill with smoke, power can fail and lifts may stop at the fire floor. Lifts are normally recalled to ground level on alarm. Only fire lifts for firefighters, and specially designed evacuation lifts where provided, are used.

ARC-238 · What are fire tender access requirements for buildings?

Roads and open space around a building must allow fire tenders and aerial ladders to approach, turn and set up near the façade. Codes specify minimum road width, turning radius, load capacity and unobstructed clearance for high-rise buildings.

Building Acoustics

ARC-239 · What is reverberation time and how is it calculated?

The time for sound level to decay by 60 dB after the source stops. Sabine's formula gives RT₆₀ = 0.161 V/A, where V is room volume in m³ and A = Σ Sα is total absorption in m² sabins.

ARC-240 · What are typical optimum reverberation times?

About 0.4–0.6 s for classrooms, about 0.7–1.0 s for lecture halls and theatres used for speech, and about 1.5–2.2 s for symphony halls. Optimum RT rises with room volume.

ARC-241 · When is the Eyring formula used instead of Sabine's?

When average absorption is high, roughly ᾱ > 0.2. Sabine then overestimates RT. Eyring gives RT = 0.161 V / [−S ln(1 − ᾱ)], which correctly tends to zero as ᾱ approaches 1.

ARC-242 · How does sound level fall with distance in free field?

For a point source, intensity follows the inverse square law, so level falls by about 6 dB per doubling of distance. For a line source such as a busy road, it falls by about 3 dB per doubling.

ARC-243 · How are decibel levels added?

Logarithmically: L_total = 10 log₁₀(Σ 10^(Lᵢ/10)). Two equal sources give +3 dB, so 70 dB + 70 dB = 73 dB. A source 10 dB quieter than another adds only about 0.4 dB.

ARC-244 · Why does a double-leaf partition insulate better than a single leaf of the same mass?

The two leaves are decoupled by an air cavity, ideally with absorbent infill, so sound must pass through two separate barriers. Above the mass–air–mass resonance frequency, performance far exceeds the mass law. Rigid ties or narrow cavities reduce the benefit.

ARC-245 · What is flanking transmission?

Sound travelling between rooms by indirect paths around a partition: through continuous floors, ceilings, façades, ducts or gaps. It limits achieved insulation, so a high-rated wall can underperform if junctions are not detailed.

ARC-246 · What is a floating floor?

A screed or slab laid on a resilient layer, such as mineral wool or rubber pads, isolated from the structural slab and walls. It reduces impact and structure-borne noise, for example under plant rooms and gyms.

ARC-247 · What is the Noise Reduction Coefficient (NRC)?

The arithmetic average of a material's absorption coefficients at 250, 500, 1000 and 2000 Hz, rounded to the nearest 0.05. It is a single-number rating for comparing absorbers at speech frequencies.

ARC-248 · What is sound masking in open-plan offices?

Adding a controlled, unobtrusive broadband background sound through ceiling loudspeakers. It reduces the intelligibility of distant speech, which improves speech privacy and reduces distraction.

ARC-249 · What is the Speech Transmission Index (STI)?

A measure from 0 to 1 of how well speech is transmitted through a room or sound system. It accounts for reverberation and background noise. Values above about 0.6 are good. It is used for classrooms, auditoria and voice alarm systems.

ARC-250 · Why are concave surfaces avoided in auditoria?

Concave walls, domes and curved rear walls focus reflections at certain spots. This creates hot spots, echoes and uneven sound. They are shaped to diffuse sound or treated with absorption.

ARC-251 · How is HVAC noise controlled in buildings?

By selecting quiet equipment, keeping duct velocities low, using lined ducts and silencers, fitting flexible connections and vibration isolators on plant, and locating plant rooms away from sensitive spaces.

Lighting & Daylighting

ARC-252 · What is daylight factor and what values are considered adequate?

DF = (indoor illuminance ÷ simultaneous outdoor illuminance under an overcast sky) × 100%. An average DF of about 2% is generally considered adequately daylit, and about 5% well daylit, though higher values can bring glare and heat gain.

ARC-253 · What are the components of daylight factor?

The sky component from direct sky view, the externally reflected component from outside obstructions, and the internally reflected component from room surfaces. DF = SC + ERC + IRC.

ARC-254 · How does the lumen method calculate the number of luminaires?

N = (E × A) ÷ (Φ × n × UF × MF), where E is required illuminance, A is area, Φ is lumens per lamp, n is lamps per luminaire, UF is the utilisation factor and MF is the maintenance factor. For 500 lux over 100 m² with 4000 lm luminaires, UF 0.6 and MF 0.8, N ≈ 26.

ARC-255 · What are the inverse square and cosine laws of illuminance?

For a point source, illuminance E = I cos θ / d², where I is intensity in candela, d is distance and θ is the angle between the light ray and the surface normal. Doubling distance quarters illuminance.

ARC-256 · What is Lighting Power Density (LPD)?

Installed lighting power divided by floor area, in W/m². Energy codes such as ECBC and ASHRAE 90.1 cap LPD by building or space type to limit lighting energy.

ARC-257 · What are spatial daylight autonomy and annual sunlight exposure?

sDA₃₀₀/₅₀% is the share of floor area that gets at least 300 lux from daylight for at least 50% of occupied hours. ASE₁₀₀₀,₂₅₀ is the share of area that gets more than 1000 lux of direct sun for more than 250 hours a year, indicating glare and overheating. LEED v4 uses both.

ARC-258 · What is Useful Daylight Illuminance (UDI)?

The percentage of occupied time when daylight illuminance falls in a useful band, commonly 100–2000 lux. Below this, daylight is too low; above it, glare and heat are likely. It gives a climate-based view of daylight quality.

ARC-259 · What is the maintenance factor in lighting design?

A factor below 1 that accounts for light loss over time from lamp lumen depreciation, lamp failure, and dirt on luminaires and room surfaces. Designs are sized so maintained illuminance still meets the target at the end of the cleaning cycle.

ARC-260 · What is the Unified Glare Rating (UGR)?

A CIE method that rates discomfort glare from luminaires for an observer position, based on luminaire luminance, size, position and background luminance. Offices typically require UGR ≤ 19. Lower values mean less glare.

ARC-261 · Why does ECBC limit window-to-wall ratio?

Glazing has much higher U-value and solar gain than opaque walls, so large WWR increases cooling load. ECBC's prescriptive path caps WWR at 40%. Larger glazing must be justified through trade-off or whole-building performance.

ARC-262 · Why is external shading more effective than internal blinds?

External shading stops solar radiation before it passes through the glass. Internal blinds absorb radiation already inside and re-emit much of it as heat into the room. External devices can cut solar gain several times more.

ARC-263 · What is the difference between direct and indirect lighting?

Direct lighting sends most light downward onto the task. It is efficient but can create glare and harsh shadows. Indirect lighting bounces light off the ceiling and walls, giving soft, uniform light with less glare but lower efficiency.

ARC-264 · What is circadian or human-centric lighting?

Lighting that varies intensity and spectrum through the day, bright and cool in the morning and warmer and dimmer in the evening, to support the body's circadian rhythm. It is assessed by melanopic metrics and suits offices, healthcare and night-shift spaces.

Climate-Responsive & Green Buildings

ARC-265 · How do LEED, GRIHA, IGBC and BREEAM differ?

LEED is the US-based global rating system. BREEAM is the UK-based system. GRIHA is India's national system, emphasising passive design and Indian benchmarks. IGBC is the CII-run Indian system, similar in structure to LEED. All score energy, water, materials, site and indoor quality.

ARC-266 · How do design strategies differ between hot-dry and warm-humid climates?

Hot-dry climates use compact forms, courtyards, thick high-mass walls, small openings, light colours and evaporative cooling, with night ventilation. Warm-humid climates use open, elongated plans, light low-mass construction, large shaded openings, raised floors and maximum cross-ventilation.

ARC-267 · How does stack ventilation work?

Warm indoor air is less dense, so it rises and leaves through high openings, drawing cooler air in through low openings. The flow rises with the height difference between openings and the indoor–outdoor temperature difference. Atria, chimneys and wind towers enhance it.

ARC-268 · How is a building designed for effective cross-ventilation?

Place inlets on the windward side and outlets on the leeward side, with outlets equal to or larger than inlets. Keep the plan shallow and avoid internal obstructions. Locate inlets at body level, and orient the façade within about 45° of the prevailing wind.

ARC-269 · What is the Energy Performance Index (EPI)?

Annual energy consumption of a building divided by its built-up area, in kWh/m²·year. It is used to benchmark buildings and set targets, for example in BEE star labelling and GRIHA.

ARC-270 · How should shading devices be chosen for different orientations in India?

South façades are best shaded by horizontal overhangs, since the sun is high. East and west façades receive low-angle sun, so vertical fins, egg-crates, louvres or movable screens work better, combined with smaller openings. North façades need little shading beyond small fins.

ARC-271 · What is RETV in Eco Niwas Samhita?

Residential Envelope Transmittance Value is the net heat gain rate through the residential building envelope, excluding the roof, per unit envelope area, in W/m². Eco Niwas Samhita 2018 (ECBC-R) limits it to 15 W/m² for most climate zones.

ARC-272 · What is an earth air tunnel?

Buried pipes, typically a few metres deep, through which air is drawn before entering the building. The ground stays near the annual mean temperature, so air is cooled in summer and warmed in winter. It reduces HVAC load.

ARC-273 · What traditional Indian elements are climate-responsive?

Courtyards, jaalis that shade while admitting breeze, jharokhas, thick masonry walls, wind towers, verandahs, sloping roofs with deep eaves in wet regions, and stepwells and water bodies for evaporative cooling.

ARC-274 · What is Life Cycle Assessment (LCA) of a building?

A method, per ISO 14040/14044 and EN 15978, that quantifies environmental impacts across all stages: material production, construction, use and operation, maintenance, demolition and end of life. It helps compare design options on embodied and operational carbon.

ARC-275 · How can water use in buildings be reduced?

Low-flow taps and showers, dual-flush WCs, waterless or low-flow urinals, rainwater harvesting, greywater and STP water reuse for flushing and landscaping, native landscaping with drip irrigation, and sub-metering to detect leaks.

ARC-276 · What is the urban heat island effect and how do buildings mitigate it?

Cities are warmer than surrounding rural areas because of dark paved surfaces, little vegetation, waste heat and trapped radiation. Buildings mitigate it with cool roofs, green roofs, shaded and permeable paving, trees and reduced waste heat.

Building Codes, Bye-laws & Planning

ARC-277 · A 1000 m² plot allows FAR 2.5 and 40% ground coverage. How many full floors can be built at maximum coverage?

Maximum floor area = 2.5 × 1000 = 2500 m². Maximum footprint = 0.40 × 1000 = 400 m². Floors = 2500 ÷ 400 = 6.25, so six full floors, with the rest as a partial floor if height and setback rules allow.

ARC-278 · What areas are commonly excluded from FAR calculation?

Typically basements and stilts used for parking and services, lift and stair wells, machine rooms, overhead tanks, refuge areas and some balcony or service areas within limits. Exclusions vary by city bye-laws, so always check the local rules.

ARC-279 · What is the NBC occupancy classification?

NBC 2016 groups buildings by use: A Residential, B Educational, C Institutional, D Assembly, E Business, F Mercantile, G Industrial, H Storage and J Hazardous, with subdivisions. The group sets fire, egress and other requirements.

ARC-280 · How do height and setback rules relate?

Bye-laws increase required setbacks and open spaces with building height, to keep light, ventilation and fire access. Height is also limited by road width, FAR, airport clearance, heritage zones and fire-fighting capability.

ARC-281 · What clearances besides the building permit may a large project need in India?

Fire NOC, airport height clearance from AAI near airports, environmental clearance for large built-up areas, heritage and monument clearances, pollution control board consents, and utility approvals for water, sewer and power.

ARC-282 · When does a building project need environmental clearance in India?

Under the EIA Notification 2006, building and construction projects with built-up area of 20,000 m² or more need prior environmental clearance. Larger townships and area development projects fall in a higher category with stricter appraisal.

ARC-283 · What is premium or purchasable FAR?

Extra floor area beyond the base FAR that a developer can buy by paying a fee to the authority, often near transit corridors. It raises density where infrastructure can support it and generates revenue.

ARC-284 · What are the compliance paths under ECBC 2017?

Prescriptive compliance meets each requirement directly. Building envelope trade-off lets better elements offset weaker ones within the envelope. Whole building performance shows by energy simulation that the proposed design uses no more energy than a standard design.

ARC-285 · What does NBC require for natural light and ventilation in habitable rooms?

Window and ventilator openings in habitable rooms should be at least about one-tenth of the floor area, with no part of the room too far from an opening. Kitchens and toilets have their own opening or mechanical-exhaust requirements.

ARC-286 · What is the minimum height of a habitable room under NBC 2016?

2.75 m from finished floor to the lowest point of the ceiling or slab soffit. Lower heights are allowed for bathrooms, corridors, kitchens in some cases and air-conditioned spaces, as specified in the code.

ARC-287 · What law mandates accessibility in Indian public buildings?

The Rights of Persons with Disabilities Act, 2016. It requires public buildings and services to meet accessibility standards within set time limits. The Harmonised Guidelines and NBC provisions set the technical requirements.

ARC-288 · What is an online building permission system?

A digital single-window platform where architects submit plans that are checked automatically against bye-laws, often with BIM or CAD rule-checking. It integrates NOCs from multiple departments and gives time-bound approvals, which improves transparency.

BIM, Digital Tools & Project Management

ARC-289 · What are 6D and 7D BIM?

Extensions beyond 3D geometry, 4D time and 5D cost. 6D is usually sustainability and energy analysis, and 7D is facility management and operations data. Usage varies, so the terms should be defined in each project's BIM plan.

ARC-290 · What is a BIM Execution Plan (BEP)?

A document agreed by the project team that defines BIM goals, uses, roles, responsibilities, software, LOD by stage, file naming, coordination process, model federation and deliverables. It responds to the client's information requirements.

ARC-291 · What are EIR, BEP and MIDP under ISO 19650?

Exchange Information Requirements (EIR) are the client's information needs. The BIM Execution Plan (BEP) is the delivery team's response explaining how to meet them. The Master Information Delivery Plan (MIDP) schedules who delivers which information and when.

ARC-292 · What is a federated model?

A combined model assembled from separate discipline models, such as architectural, structural and MEP. Each discipline keeps ownership of its model. Federation is used for coordination, clash detection and review.

ARC-293 · What is COBie?

Construction Operations Building information exchange, a structured spreadsheet or data format for handing over asset data: spaces, equipment, manufacturers, warranties and maintenance information. It is passed from the BIM model to facility managers.

ARC-294 · What are CPI and SPI in earned value management?

Cost Performance Index CPI = EV/AC and Schedule Performance Index SPI = EV/PV, where EV is earned value, AC actual cost and PV planned value. Values below 1 mean over budget or behind schedule.

ARC-295 · How is the expected activity time calculated in PERT?

tₑ = (o + 4m + p)/6, where o, m and p are optimistic, most likely and pessimistic estimates. Variance = ((p − o)/6)². For o = 4, m = 6, p = 14 days, tₑ = 7 days.

ARC-296 · What is total float and free float?

Total float is how long an activity can be delayed without delaying the project: TF = LS − ES = LF − EF. Free float is how long it can be delayed without delaying the early start of any following activity.

ARC-297 · What are common construction contract types?

Lump-sum fixed price, item-rate or measured contracts priced on a BOQ, cost-plus contracts, EPC or design-and-build where one party designs and builds, and construction management. Each allocates risk differently between client and contractor.

ARC-298 · What is scan-to-BIM?

Capturing an existing building with laser scanning or photogrammetry to produce a dense point cloud, then modelling BIM elements from it. It is used for renovation, retrofit, heritage documentation and as-built verification.

ARC-299 · Which tools are used for building energy simulation?

EnergyPlus, often through DesignBuilder or OpenStudio, eQUEST, IES-VE and TRNSYS. They model hourly heat transfer, HVAC and lighting with weather files to predict energy use and check compliance with ECBC, ASHRAE 90.1 or LEED.

ARC-300 · What is a digital twin of a building?

A live digital model of a building linked to real-time data from sensors, BMS and IoT devices. It mirrors actual performance, and is used for monitoring, predictive maintenance, energy optimisation and testing operational scenarios.

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