LESSON 2.2 — Building Construction Techniques
A. Standard Map
| Topic | Governing Source | Exam Focus |
|---|---|---|
| Load-bearing vs framed construction | NBC 2016 Part 6; IS:1905:2002 | Selection logic; height and span limits |
| Foundation types | IS:6403:1981 (shallow); IS:2911:1979 (piles) | Selection by soil and load; pile types |
| Masonry bond types | IS:2212:1991 — Code of Practice for Brickwork | English, Flemish, Stretcher — arrangement rules |
| RCC construction sequence | IS:456:2000; IS:2505 (concrete vibrators) | Pour sequence; curing period |
| Roof systems | NBC 2016 Part 6; standard construction practice | Type identification by shape and construction |
| Stairs — dimensional standards | NBC 2016 Part 4; IS:1948 | Rise–going rule (2R+G); type identification |
| Modular coordination | IS:1628:1974; NBC 2016 Part 3 | Basic module 100 mm; preferred dimensions |
B. Mechanism in Words
- A structural scheme begins with the decision of how vertical loads are carried: by thick walls (load-bearing) or by a separate skeletal frame (framed).
- Loads from the superstructure flow down to the ground through the foundation; the foundation type is matched to the soil bearing capacity and the magnitude of the load.
- Masonry is laid in specific patterns (bonds) that interlock bricks across wall thickness — bond geometry determines structural efficiency.
- In RCC construction, formwork holds wet concrete in shape; reinforcement carries tension; concrete carries compression; the two work together after the concrete hardens and formwork is removed.
- The roof seals the building envelope — its form determines drainage, structural span, and load distribution.
- Stairs connect floor levels; their dimensional geometry must satisfy comfort (2R+G formula) and code minima for width, rise, and going.
C. Core Concept Explanations
C1. Load-Bearing vs Framed Construction
| Property | Load-Bearing Masonry | Framed Construction (RCC/Steel) |
|---|---|---|
| Load path | Loads carried by walls → foundation | Loads carried by columns and beams → foundation |
| Wall material | Brick, stone, or block masonry (structural) | Walls are non-structural infill (partition) panels |
| Floor/roof span | Limited by wall spacing (up to ~4–5 m economically) | Beams bridge between columns; span up to 6–12 m+ economically |
| Height limit | Generally ≤ 3 storeys (IS:1905) | Effectively unlimited with appropriate column design |
| Opening limitation | Openings weaken walls; lintel over every opening required | No restriction — partitions independent of structure |
| Economy | Economical for small residential (<3 storeys, <5 m span) | Economical for medium-to-large buildings |
| Seismic behaviour | Poor ductility; poor in seismic zones III–V | Better ductility with IS:13920 detailing |
Source: IS:1905:2002 (Structural Use of Unreinforced Masonry); NBC 2016 Part 6.
Exam Anchor: Load-bearing construction is limited to 3 storeys per IS:1905 recommendations in Indian practice. For seismic zones III, IV, and V, load-bearing masonry requires specific reinforcement detailing per IS:4326.
C2. Foundation Types — Selection Logic
| Foundation Type | Mechanism | Best For | Selection Criterion |
|---|---|---|---|
| Strip footing | Continuous strip of concrete beneath a load-bearing wall | Load-bearing masonry buildings; moderate loads | Good soil bearing capacity; loads distributed along a wall |
| Isolated (pad) footing | Individual rectangular or square pad under each column | Framed buildings; columns with well-spaced loads | Firm soil; columns spaced ≥ 2–3 m apart |
| Combined footing | Single footing supporting two or more columns | Columns too close together for individual footings; property line constraint | Closely spaced columns; one column near boundary |
| Raft (mat) foundation | Single slab covering the entire building footprint | Weak soil (low bearing capacity); heavy loads; basement structures | Bearing capacity too low for individual footings |
| Pile foundation | Long slender shafts transferring load to deeper strata | Soft soil near surface; heavy loads; where shallow founding is impossible | Soft/compressible surface layer; waterlogged sites; high column loads |
Pile types:
| Pile Type | Load Transfer | Example |
|---|---|---|
| Friction pile | Load transferred primarily through skin friction along pile shaft | Soft clay sites where hard stratum is very deep |
| End-bearing pile | Load transferred to hard stratum at pile tip | Soft surface layer over dense gravel, rock, or dense sand |
| Bored cast-in-situ pile | Hole bored, reinforcement cage placed, concrete poured in situ | Where vibration is unacceptable (near existing structures) |
| Driven precast pile | Precast pile driven by hammer | Where bored piling is impractical; sandy or gravelly soils |
Source: IS:6403:1981 (shallow foundations); IS:2911 Part 1/Sec 2:1979 (bored piles).
C3. Masonry Bond Types (IS:2212:1991)
| Bond | Course Arrangement | Min. Wall Thickness | Key Property |
|---|---|---|---|
| English Bond | Alternate courses: one course ALL headers, next course ALL stretchers; quoin closer next to corner header | One brick (200 mm) | Strongest structural bond — no continuous vertical joints; max transverse bond |
| Flemish Bond | Each course has ALTERNATING headers and stretchers; every course begins with quoin closer | One brick (200 mm) | Better appearance than English Bond; slightly less strength due to some vertical joint alignment |
| Stretcher Bond (Running Bond) | All courses = stretchers only; each course offset by half brick | Half brick (100 mm) | Suitable ONLY for half-brick thick partition walls or cavity wall inner leaves; cannot be load-bearing on its own |
| Rat Trap Bond | Bricks placed on edge (vertical), creating internal cavity | One brick (200 mm) | ~25% less brick+mortar; internal air cavity = thermal insulation; surface appearance like Flemish Bond |
Source: IS:2212:1991; ch12-part01.
Exam Anchor — Most tested distinction:
– English Bond: WHOLE COURSES alternate — one course all headers, next all stretchers.
– Flemish Bond: EVERY COURSE mixes headers and stretchers alternately.
– Visual clue: English Bond shows bands of solid colour; Flemish Bond shows a regular mixed pattern in every course.
Mortar proportions:
| Mortar Mix (Cement:Sand) | Application |
|---|---|
| 1:3 | High-strength masonry; plinth level and below DPC; parapet walls |
| 1:4 | Load-bearing masonry above plinth; sills and copings |
| 1:6 | General non-load-bearing internal masonry |
| 1:8 | Filling, backing of thick walls; low-strength work |
C4. RCC Construction Sequence
- Set up formwork: Shutters for columns, walls, beams, and slabs erected and aligned.
- Steel placement: Reinforcement bars cut, bent, and placed per bar bending schedule; cover blocks placed to maintain specified cover.
- Inspection: Cover, laps, and bar diameters verified before concreting.
- Concrete mixing and placement: Concrete mixed at design w/c ratio; placed in layers ≤ 300 mm; not dropped from height > 1.5 m to prevent segregation.
- Compaction: Needle vibrator or table vibrator used; vibrator not placed directly on reinforcement; vibrated at ~450 mm intervals; immersion time ~15 seconds per position.
- Curing: Concrete protected from drying for minimum 7 days (OPC) or 14 days (PPC/slag cement); methods include ponding, wet burlap, curing compound.
- Formwork removal (striking): Minimum periods per IS:456 — column/wall sides = 24–48 hours; beam/slab soffits = 14–21 days.
Source: IS:456:2000, Clause 13 (formwork removal times); Clause 14 (concreting); Clause 21 (curing).
Exam Anchor: Minimum curing period for OPC concrete = 7 days. Minimum for PPC/slag cement = 14 days (slower hydration requires longer curing).
Cover requirements (IS:456, Clause 26.4):
| Member | Minimum cover to main reinforcement | Severe exposure |
|---|---|---|
| Slab | 20 mm | 30 mm |
| Beam | 25 mm | 35 mm |
| Column | 40 mm | 50 mm |
| Foundation | 50 mm | — |
C5. Roof Systems
| Roof Type | Form | Structural Principle | Application |
|---|---|---|---|
| Flat roof | Horizontal or near-horizontal slab | RCC slab spanning between beams/columns; waterproofing layer essential | Most common urban building type; allows roof terrace |
| Pitched roof | Sloped triangular form | Rafter-purlin-truss system; slope sheds rainwater; suited for high rainfall regions | Residential bungalows; industrial sheds |
| Shed/mono-pitch | One sloped plane | Simple rafter system | Industrial buildings; ancillary structures |
| Shell roof | Doubly curved thin concrete surface | Compression-dominant; self-stiffening through curvature | Long-span structures; auditoriums; warehouses |
| Folded plate | Flat slabs folded into angular profile | Thin concrete gains stiffness through folding | Medium-span roofs; can span 20–30 m |
| Space frame | 3D triangulated steel network | Spread loads triaxially; very efficient material use | Long-span column-free halls; airports; stadia |
Exam Anchor: Shell and folded plate roofs are classified as form-active structures — their efficiency comes from shape, not material. A thin concrete shell roof can span 50+ m using less material than a conventional beam-column system.
C6. Stair Types and Dimensional Standards
Stair types (by geometry):
| Type | Description | Use |
|---|---|---|
| Dog-leg stair | Two parallel flights connected by a half-landing; flights go in opposite directions | Most common in residential and commercial buildings; space-efficient |
| Open newel stair | Similar to dog-leg but with a gap (well) between flights; decorative newel post | Institutional buildings; wider landings |
| Spiral stair | Circular plan; single column (newel) at centre | Emergency egress; space-constrained access; not primary escape route |
| Scissor stair | Two interleaved dog-leg stairs sharing the same footprint | Fire-escape arrangements; minimises area per stair |
| Flying stair | No visible support; stairs appear to project from wall only | Feature staircases in public buildings |
2R + G dimensional rule:
| Variable | Definition | Code Limit | Comfort Range |
|---|---|---|---|
| R (Riser) | Vertical height of one step | R ≤ 190 mm (NBC 2016) | 150–175 mm (preferred) |
| G (Going/Tread) | Horizontal depth of one step (nosing to nosing) | G ≥ 250 mm (NBC 2016) | 250–300 mm |
| 2R + G | Comfort check formula | — | 600–650 mm |
Worked check:
R = 175 mm, G = 280 mm → 2(175) + 280 = 350 + 280 = 630 mm ✓ (within 600–650 mm)
Source: NBC 2016 Part 4; IS:1948 (stairs).
Note: 2R + G = 600–650 mm is the comfort CHECK formula — used to verify that an R–G combination is ergonomically acceptable. It is NOT solved simultaneously for R and G; each is independently limited by code.
C7. Modular Coordination (IS:1628:1974)
Basic Module (M) = 100 mm. All building component dimensions should be multiples of 100 mm.
| Level | Increment | Use |
|---|---|---|
| Basic module | 100 mm (1M) | Component dimensions: bricks, blocks, tiles, panels |
| Multimodule | 300 mm (3M) | Room dimensions; structural grid spacing for small buildings |
| Multimodule | 600 mm (6M) | Bay dimensions; structural grids for medium buildings |
| Multimodule | 1200 mm (12M) | Structural grids for large buildings; planning grids |
Exam Anchor: India’s basic module = 100 mm. The concept ensures that prefabricated components (bricks, blocks, tiles, windows) fit together with minimal cutting and waste. International ISO basic module is also 100 mm — same value.
D. Design/Parameter Table
| Parameter | Value | Unit | Source |
|---|---|---|---|
| Load-bearing masonry max height (IS:1905) | ≤ 3 storeys | storeys | IS:1905:2002 |
| Basic module | 100 | mm | IS:1628:1974 |
| Max. riser height | 190 | mm | NBC 2016 Part 4 |
| Min. going (tread) | 250 | mm | NBC 2016 Part 4 |
| 2R + G comfort range | 600–650 | mm | NBC 2016 |
| Min. OPC curing period | 7 | days | IS:456 Cl. 21 |
| Min. PPC/slag curing period | 14 | days | IS:456 Cl. 21 |
| Concrete layer thickness (max pour) | 300 | mm | IS:456 Cl. 13 |
| Max height of concrete drop (segregation) | 1500 | mm | IS:456 Cl. 13 |
| Vibrator immersion time (approx.) | ~15 | seconds | IS:456 Cl. 13 |
| Vibrator spacing | ~450 | mm | IS:456 |
| Column/wall side formwork — min. removal | 24–48 | hours | IS:456 Cl. 11 |
| Beam/slab soffit formwork — min. removal | 14–21 | days | IS:456 Cl. 11 |
| Slab minimum cover | 20 | mm | IS:456 Cl. 26.4 |
| Column minimum cover | 40 | mm | IS:456 Cl. 26.4 |
| Foundation minimum cover | 50 | mm | IS:456 Cl. 26.4 |
E. Common Confusions
| Confusion | Correct Distinction |
|---|---|
| Dog-leg vs open newel stair | Dog-leg has NO gap between flights; open newel has a gap (well) and is decorative. Both have two flights reversing direction at a landing. |
| English Bond vs Flemish Bond | English Bond = alternating WHOLE COURSES of headers and stretchers. Flemish Bond = headers and stretchers WITHIN THE SAME COURSE alternating. Visual clue: English shows bands; Flemish shows a regular mixed pattern in every course. |
| Stretcher Bond load-bearing use | Stretcher Bond is for HALF-BRICK partitions only — it cannot be used as a load-bearing wall because there are no headers tying across the wall thickness. |
| 2R + G = a formula to find G | It is a COMFORT VERIFICATION check. G and R are each independently constrained by code limits (R ≤ 190, G ≥ 250). The check verifies that the chosen combination is comfortable. |
| Curing period OPC vs PPC | OPC = 7 days minimum. PPC (Portland Pozzolana Cement) and slag cement = 14 days minimum. PPC hydrates slower; shorter curing produces weaker concrete. |
| Raft foundation vs pile foundation | Raft spreads load over a wide area at shallow depth. Pile transfers load to deep strata. Both used for weak surface soils but for different reasons — raft works when bearing capacity is low but sufficient with a larger area; piles when even a raft would be inadequate or settlement would be unacceptable. |
F. Exam Traps
| Trap | Incorrect Assumption | Correct Answer |
|---|---|---|
| T07 | “Flemish Bond is stronger than English Bond” | English Bond is structurally stronger — no continuous vertical joints; better transverse bond. Flemish Bond is more attractive but slightly weaker. |
| T08 | “Stretcher Bond can be used for load-bearing walls” | Stretcher Bond is for half-brick partitions ONLY — no headers cross the wall thickness; cannot carry transverse loads or act structurally. |
| T09 | “Minimum curing period is 14 days for all concrete” | 14 days is for PPC/slag cement. For OPC, minimum is 7 days. The 14-day figure applies to pozzolanic/blended cements which hydrate more slowly. |
| T10 | “Vibrator should be placed on the reinforcement bars” | Placing the vibrator directly on bars causes segregation and can displace bars. The vibrator must be inserted into the concrete between bars. |
| T11 | “Basic module in India = 300 mm” | Basic module = 100 mm (IS:1628:1974). 300 mm is a multimodule (3M); 1200 mm is the planning grid (12M). |
| T12 | “Column/wall formwork must remain for 14 days before striking” | Column/wall SIDE formwork (not soffit) can be struck after 24–48 hours as these faces are not load-bearing formwork — the slab/beam soffit must wait 14–21 days. |
G. Answer-Writing Cues
For bond-type identification:
“English Bond places alternate courses entirely as headers and stretchers. In Flemish Bond, headers and stretchers alternate within every course. English Bond provides maximum transverse bond strength and is preferred for structural load-bearing walls. Flemish Bond is used where appearance is a priority.”
For foundation selection:
“Foundation type is selected based on soil bearing capacity and structural load. Isolated footings are used for framed buildings with firm soil and well-spaced columns. Where soil bearing capacity is low and individual footings would either overlap or settle excessively, a raft foundation spreading load over the entire footprint is appropriate. Piles are required when soft or compressible soil extends to substantial depth and even a raft cannot provide adequate settlement control.”
H. PYQ Linkage Note
| Topic | Exam Appearance | Pattern |
|---|---|---|
| English Bond vs Flemish Bond | GATE, UPSC-CPWD, state PSC multiple years | MCQ: describe a bond; identify it; OR identify from image description |
| Stretcher Bond limitation | GATE | MCQ: “Stretcher bond is used for walls of minimum thickness…” |
| 2R + G formula | GATE multiple years | MCQ: given R and G, check if combination is satisfactory; NAT possible |
| Minimum curing period | GATE, UPSC-CPWD | MCQ: OPC vs PPC distinction; 7 vs 14 days |
| Foundation type selection | UPSC-CPWD, state PSC | MCQ: match soil condition/load scenario to foundation type |
| Basic module | GATE, UPSC-CPWD | MCQ: “India’s basic module for modular coordination is…” |
I. Mini-Check — Lesson 2.2 (5 Questions)
Q1 (MCQ): A masonry wall is constructed such that every course contains alternating headers and stretchers, with every course beginning with a quoin closer adjacent to the corner header. This describes:
(A) English Bond (B) Flemish Bond (C) Stretcher Bond (D) Rat Trap Bond
A1: (B) Flemish Bond. The key identifier: headers and stretchers WITHIN THE SAME COURSE. English Bond would have whole courses alternating — one course all headers, next all stretchers.
Q2 (MCQ): A staircase has a riser (R) = 160 mm and a going (G) = 290 mm. Is this combination acceptable per NBC 2016?
(A) No — riser exceeds maximum (B) No — 2R + G falls outside comfort range (C) Yes — both code limits satisfied; 2R + G = 610 mm ✓ (D) No — going is below minimum
A2: (C) Yes. R = 160 mm ≤ 190 mm ✓; G = 290 mm ≥ 250 mm ✓; 2R + G = 2(160) + 290 = 320 + 290 = 610 mm → within 600–650 mm ✓. All conditions satisfied.
Q3 (MCQ): Per IS:456:2000, what is the minimum period of water curing required for structural RCC made with Portland Pozzolana Cement (PPC)?
(A) 3 days (B) 7 days (C) 14 days (D) 28 days
A3: (C) 14 days. PPC (pozzolanic/blended cement) hydrates more slowly than OPC. IS:456 requires a minimum of 14 days for PPC, slag cement, and other blended cements. OPC requires 7 days.
Q4 (MCQ): Stretcher Bond (Running Bond) is suitable only for masonry walls of minimum thickness:
(A) 200 mm (one brick) (B) 150 mm (C) 100 mm (half brick) (D) 300 mm
A4: (C) 100 mm (half brick). Stretcher Bond uses only stretchers in every course — no headers cross the wall thickness. It is therefore suitable only for half-brick (100 mm) partition walls. Load-bearing walls require at least English or Flemish Bond (one full brick = 200 mm).
Q5 (NAT): The staircase in a residential building has a total floor-to-floor height of 3000 mm and a going (tread) of 275 mm. Using the 2R + G formula with a target value of 625 mm, find the required riser height (R). How many risers are in the flight? (Answer: riser height in mm; number of risers as integer.)
A5:
– From 2R + G = 625 → 2R = 625 − 275 = 350 → R = 175 mm
– Check: R = 175 mm ≤ 190 mm ✓; G = 275 mm ≥ 250 mm ✓; 2R + G = 350 + 275 = 625 ✓
– Number of risers = 3000 ÷ 175 = 17.14 → 18 risers (round up; each step slightly under 175 mm)
– Actual riser = 3000 / 18 = 166.7 mm — recheck 2R + G = 2(166.7) + 275 = 333.4 + 275 = 608 mm ✓
Riser: 175 mm (target) / 166.7 mm (actual with 18 risers); Risers: 18