Building technology

Building technology is the practical knowledge of how buildings are put together — masonry, carpentry, plastering, painting, roofing, flooring and damp-proofing — and the building by-laws that control what may be built where. In Nepal, most houses are RCC frames with brick infill or load-bearing masonry, and the 2015 Gorkha earthquake underlined the need for good workmanship and code compliance. This note covers the essentials examiners like to test.

Key concepts

Brick masonry

• Bonds: English bond (alternate courses of headers and stretchers; strongest, used for load-bearing walls), Flemish bond (headers and stretchers alternate in each course; better appearance), stretcher bond (half-brick walls/partitions), header bond (curved walls, footings).
• Rules: avoid continuous vertical joints, use queen closers next to quoin headers, wet bricks before laying, lay frog up, joint thickness ~10 mm, lift not more than about 1–1.5 m per day.
• Mortar: cement-sand 1:4 to 1:6 for walls.

Stone masonry

• Rubble masonry – random/coursed rubble, dry rubble (no mortar).
• Ashlar masonry – finely dressed stones with thin joints (≤ 3 mm for fine ashlar).
• Through-stones (bond stones) must be placed at regular, close intervals both along the wall and up its height to tie the two wall faces together — a key earthquake-resistant measure in Nepali stone houses.

Carpentry

• Door/window frames (chaukhat) in sal or seasoned hardwood, shutters (panelled, flush, glazed, louvered), joints (mortise and tenon, dovetail, lap, scarf), fixtures (hinges, tower bolts).
• Timber must be seasoned and treated against termites and decay.

Plastering

• Purpose: smooth, durable, weatherproof finish and base for paint.
• Typical mixes: 1:4 external, 1:6 internal (cement:sand); thickness 12 mm (internal) to 15–20 mm (external, in two coats).
• Process: rake joints, wet surface, apply ground marks, apply plaster, cure for 7 days.
• Defects: cracking, blistering, efflorescence, popping (lime nodules), peeling.

Painting

• Steps: surface preparation (clean, sand, fill cracks) → primer → putty (walls) → undercoat → finish coats (usually two).
• Wood: knotting, priming, stopping, then coats. Steel: remove rust, red oxide/zinc primer.
• Defects: blistering (moisture), flaking, chalking, wrinkling, bloom, fading.

Concrete roofing

• RCC slab (one-way when $l_y/l_x > 2$, two-way when ≤ 2), flat slab, ribbed/waffle slab.
• Good practice: proper cover (~15–20 mm for slabs), vibration, curing ≥ 7 days (OPC), formwork removal times (IS 456 with OPC: slab soffit 3 days with props refixed, props for slabs up to 4.5 m span 7 days, above 4.5 m 14 days), roof slope or screed and waterproofing (bitumen, membrane, brick-bat coba) to prevent leakage.

Flooring

• Components: base course (soling/sub-base), PCC bed, and floor finish.
• Types: cement concrete (IPS), terrazzo, mosaic, ceramic/vitrified tiles, marble, timber, stone slabs.
• Selection: durability, cleanliness, appearance, cost, slip resistance, sound insulation.

Damp-proof course (DPC)

• Prevents rising dampness from the ground through walls.
• Location: at plinth level, usually 150 mm above ground, across full wall thickness.
• Materials: 25–40 mm cement concrete (1:2:4 or 1:1.5:3) with waterproofing compound and bitumen coat, bitumen felt, polythene sheets, slate, mastic asphalt.
• Other methods: cavity walls, surface treatment, integral waterproofing.

Building by-laws

• Rules set by municipalities under the Local Government Operation Act 2074, Building Act 2055 and the applicable planning and building by-laws/standards (e.g. Kathmandu Valley Development Authority by-laws and national standards issued through DUDBC).
• Typical controls: Floor Area Ratio (FAR), ground coverage, setback from road and boundaries, right of light (angle/height plane), maximum height based on road width, parking, open space, fire exits.
• Permit procedure: design approval (naksa pass) — plans signed by registered engineers/architects — then construction supervision, completion certificate.
• NBC compliance, including NBC 105 seismic design, is mandatory.

High-yield points

• English bond is strongest; Flemish bond looks better; a queen closer is placed next to the quoin header.
• DPC at plinth level, commonly 40 mm cement concrete with a waterproofing compound.
• Slab is one-way when $l_y/l_x > 2$, two-way when ≤ 2.
• IS 456 (OPC) formwork: slab soffit 3 days; slab props 7 days (span ≤ 4.5 m) or 14 days (> 4.5 m).
• FAR = total floor area ÷ plot area; ground coverage = plinth area ÷ plot area.

Formulas

$\text{FAR} = \frac{\text{Total built-up floor area of all floors}}{\text{Plot area}}$ $\text{Ground coverage}(\%) = \frac{\text{Plinth area}}{\text{Plot area}}\times100$

Worked example

A plot of 300 m² allows ground coverage 60% and FAR 2.5. What is the maximum plinth area and how many full floors can be built at that plinth area?

• Maximum plinth area = 0.6 × 300 = 180 m²
• Maximum total floor area = 2.5 × 300 = 750 m²
• Number of floors = 750/180 = 4.17 → 4 full floors of 180 m² (720 m²), with 30 m² remaining.

Exam tips

• English bond is strongest; Flemish bond looks better; avoid continuous vertical joints.
• DPC is at plinth level; common thickness 40 mm concrete with waterproofing.
• Through-stones in stone masonry and bands (plinth, sill, lintel, roof) are key seismic features.
• FAR uses total floor area; ground coverage uses only the plinth footprint.
• Curing of plaster and concrete: at least 7 days for OPC.

Exam-style questions

From Calmon's question bank, which has 25 questions on this topic.

1. In building bylaws, the minimum open distance to be kept between a building and the plot boundary or road is called the

• A. Ground coverage
• B. Plinth area
• C. Floor area ratio
• D. Setback

Answer: D. Setback is the minimum distance from the plot boundary or road line within which construction is not allowed.

2. In stone masonry, a through stone (bond stone) is a stone that

• A. Is placed only at the corners
• B. Projects out of the wall as a cornice
• C. Extends through the full thickness of the wall
• D. Is used only in the foundation

Answer: C. A through stone runs across the full thickness of the wall and ties the two faces together.

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