Amogh N P
✦ In loving memory of Amogh N P — Architect · Designer · Visionary ✦
A roof of exposed timber king-post trusses in a heritage hall.
Unit V25ARS122 · Building Materials & Construction I

Timber — Roofing & Joinery

Trusses, joints, and the great timber roofs of South India.

≈ 35 min + studio task

Timber is the original engineered material — strong, light, warm, and worked entirely by hand. This lesson covers the Indian structural timbers and why they are seasoned, the trusses that let a roof span without internal walls, the joints that hold them, and one of the great roofs of South India — the Madras terrace.

Learning objectives

By the end of this lesson, you will be able to — mapped to the course outcomes for Building Materials & Construction I:

1
CO5 · Understand

Identify the main Indian structural timbers and why timber is seasoned.

2
CO5 · Understand

Name the members of a king-post and queen-post truss and explain why a truss works.

3
CO5 · Apply

Match common carpentry joints to where they are used.

4
CO6 · Evaluate

Read the layered build-up of a Madras terrace roof.

Know your wood

Timber as a material

Indian construction draws on a few prized structural timbers. All must be seasoned — dried to reduce moisture — before use, or they warp, split and rot. The structural code IS 883 sorts timber into strength groups by stiffness.[1]

TimberCharacterUse
Teak (Tectona grandis)premier hardwoodStrong, durable, dimensionally stable, free of bad seasoning defects — doors, frames, furniture, structure.[2]
Sal (Shorea robusta)heavy hardwoodVery strong and hard, slow to season (refractory) — beams, sleepers, piles.[2]
Deodar (Cedrus deodara)strongest Indian coniferLight, durable softwood — construction, beams, window frames, shingles.[2]
Spanning the gap

Pitched-roof trusses

A truss is a triangle: when a load pushes down on the sloping rafters, they try to spread the walls apart, and the horizontal tie beam in tension holds them in. The wider the span, the more members you add. Select a truss.[4]

Lean-to (mono-pitch)

The simplest roof — rafters on a single slope between a high and a low wall. Spans up to about 2.4 m.[3]

King post truss — triangulation carries the roof Tie beam (in tension — stops the walls spreading) Principal rafter Principal rafter King post Strut Strut Ridge Suits spans of about 5–8 m. The king post hangs the tie beam; the struts stop the rafters sagging.
DiagramA king post timber roof truss with its members labelled: tie beam, two principal rafters, central king post, two struts and the ridge
A king-post truss showing tie beam, rafters, king post and struts.
PhotoA king-post truss showing tie beam, rafters, king post and struts.
How wood meets wood

Timber joinery

With no bolts, traditional carpentry holds itself together with cut joints — each shaped for the forces it must carry.[7]

Two joints that frame a building Mortise & tenon mortise (slot) tenon (tongue) Dovetail flared pins resist pulling apart Mortise & tenon frames doors, windows and truss members; the dovetail locks drawer and box corners.
DiagramTwo traditional timber joints: a mortise and tenon, and a dovetail
Carpentry joints close-up — dovetail and mortise-and-tenon.
PhotoCarpentry joints close-up — dovetail and mortise-and-tenon.
Mortise & tenon

A tenon (tongue) fits a mortise (slot) — the strong framing joint for doors, windows and truss members.

Dovetail

Interlocking flared pins resist pulling apart — drawer, box and cabinet corners.

Halved (halving)

Half-depth cut from each member so faces sit flush at a crossing.

Bridle

An open mortise receives a tenon — common at strut-to-tie junctions in trusses.

Tongue & groove

A tongue on one board enters a groove in the next — floor and wall boarding.

Dowelled

Inserted dowels (wood or metal) lock the ends together — strong and concealed.

A traditional teak panelled door with stiles, rails and raised panels.
PhotoA traditional teak panelled door with stiles, rails and raised panels.
A flat roof of timber, brick & lime

The Madras terrace roof

The Madras terrace roof is the great flat roof of South India — prized for being durable and cool in the heat. It is built up in clear layers.

The Madras terrace roof — a flat, cool, durable roof Finish / weathering coat Lime concrete topping Flat bricks on edge, herringbone, in lime mortar Teak joists Bricks laid at ~45° span between closely-spaced joists; the lime mass keeps interiors cool in the South-Indian heat.
DiagramSection through a Madras terrace roof: teak joists carrying flat bricks laid on edge in a herringbone pattern in lime mortar, topped with lime concrete and a finish
The underside of a Madras terrace roof — brick-on-edge between teak joists.
PhotoThe underside of a Madras terrace roof — brick-on-edge between teak joists.
  1. 1Timber joists (usually teak) spanning the shorter way at close spacing.
  2. 2Flat 'Madras terrace' bricks laid on edge at ~45° in a herringbone pattern, bedded in lime mortar.
  3. 3A lime-concrete (brick-bat) topping to level and weatherproof.
  4. 4A smooth finish / weathering coat on top.

Build-up after Brick&Bolt / Estate Orbits construction guides.[6]

A Mangalore-tiled roof seen from below, on its timber rafters and battens.
PhotoA Mangalore-tiled roof seen from below, on its timber rafters and battens.
Check your understanding

Self-assessment

1. Why does a roof truss work?

2. Which truss suits the widest span (8–12 m)?

3. In a Madras terrace roof, what are laid on edge between the joists?

In a nutshell

Recap

Indian structural timbers include teak, sal and deodar; timber is seasoned to cut moisture for strength and stability.
A truss is a triangle: the tie beam in tension resists the rafters' outward thrust.
King-post trusses span ~5–8 m, queen-post ~8–12 m; lean-to, couple and collar roofs cover smaller spans.
The Madras terrace roof layers teak joists, brick-on-edge in lime mortar, and a lime-concrete topping into a flat, cool roof.
The evidence

References & further reading

  1. [1]IS 883:2016 — Design of Structural Timber in Buildings — Code of Practice (Fifth Revision). BIS. https://archive.org/details/gov.in.is.883.2016
  2. [2]Indian structural timbers (teak, sal, deodar) — properties and uses; IS 399 classification. https://law.resource.org/pub/in/bis/S03/is.399.1963.pdf
  3. [3]Pitched-roof types and spans (lean-to, couple, collar). First in Architecture — roof construction details. https://www.firstinarchitecture.co.uk/detail-post-pitched-roof-details/
  4. [4]King post truss — members and spans. Gharpedia. https://gharpedia.com/blog/king-post-truss/
  5. [5]Queen post truss — members and spans. Firgelli Automations technical blog. https://www.firgelliauto.com/blogs/mechanisms/queen-post-roof-truss
  6. [6]Madras terrace roof — construction build-up. Brick&Bolt construction guide; Estate Orbits. https://www.bricknbolt.com/blogs-and-articles/construction-guide/madras-terrace-roof
  7. [7]Timber joints in carpentry and joinery. CivilEngPro. https://civilengpro.com/timber-joints-in-carpentry-and-joinery/

Further reading

  • Punmia, B.C., Jain, A.K. & Jain, A.K. Building Construction (Carpentry & Joinery). New Delhi: Laxmi Publications.
  • Rangwala, S.C. Building Construction. Anand: Charotar Publishing House.
  • McKay, W.B. Building Construction (carpentry & joinery volume). London: Routledge.
  • IS 1003 (Parts 1 & 2) — Timber Panelled and Glazed Shutters. BIS.

Sources gathered and fact-checked June 2026. Published values vary by source, sample and method — treat as indicative and confirm against the cited standard before structural use.