Timber in Building Construction

Study Material: Timber

1. Introduction

Timber is one of the oldest and most widely used natural construction materials. It is obtained from trees and has been used for buildings, furniture, doors, windows, roofs, bridges, and many other purposes.

Timber is valued because of its:

Natural appearance
High strength-to-weight ratio
Ease of working
Good thermal insulation
Good acoustic properties
Renewable nature
Availability in different sizes and forms

However, timber must be properly seasoned, preserved, and selected to ensure durability and structural performance.

Timber in Building Construction

2. Meaning of Timber

Timber is wood that is suitable for engineering, building, and other construction purposes.

Wood obtained from a freshly felled tree contains a considerable amount of moisture. Such wood is called green timber.

Green Timber

Green timber is freshly cut wood that contains a high percentage of moisture.

Green timber is generally unsuitable for immediate construction because it may:

Shrink after drying
Warp or twist
Develop cracks
Lose strength
Become vulnerable to fungal attack
Cause dimensional instability in building components

Therefore, green timber is usually subjected to a process called seasoning before use.

Timber in Building Construction

3. Advantages of Timber

3.1 High Strength-to-Weight Ratio

Timber is comparatively light in weight but can possess considerable strength. This makes it suitable for roofs, beams, columns, doors, and other building components.

3.2 Easy to Work

Timber can be easily:

Cut
Sawed
Planed
Drilled
Nailed
Screwed
Joined
Carved

This makes timber convenient for construction and interior applications.

3.3 Thermal Insulation

Timber has good thermal insulation properties compared with many conventional construction materials.

Thermal insulation means the ability of a material to slow down the transfer of heat. Timber does not conduct heat as readily as metals such as steel. Therefore, it can help reduce heat transfer between the interior and exterior of a building.

However, timber does not completely stop heat transfer. It only slows down the movement of heat.

3.4 Acoustic Properties

Timber can absorb and diffuse sound to some extent. It is therefore used in:

Auditoriums
Music rooms
Interior wall panels
Ceiling treatments
Recording studios
Decorative acoustic surfaces

3.5 Natural Appearance

Timber has an attractive grain, texture, and colour. It is widely used for architectural and interior applications because of its natural appearance.

3.6 Renewable Material

Timber is obtained from trees and can be considered a renewable material when forests are managed responsibly and trees are replanted.

3.7 Good Workability

Timber can be joined using:

Nails
Screws
Bolts
Adhesives
Wooden joints

This makes it suitable for both structural and decorative work.

3.8 Electrical Insulation

Dry timber is a poor conductor of electricity. It may therefore provide some electrical insulation. However, its electrical resistance decreases when it becomes wet.

Timber in Building Construction

4. Applications of Timber

Timber is used in a wide range of construction and non-construction activities.

4.1 Structural Applications

Timber is used for:

Beams
Columns
Roof trusses
Rafters
Purlins
Floor joists
Temporary supports
Formwork
Scaffolding

4.2 Architectural Applications

Timber is used for:

Doors
Windows
Frames
Partitions
Flooring
Wall panelling
False ceilings
Staircases
Handrails

4.3 Furniture Applications

Timber is used for:

Tables
Chairs
Beds
Cupboards
Shelves
Cabinets
Desks

4.4 Decorative Applications

Timber is used for:

Interior decoration
Carved panels
Decorative screens
Wall cladding
Ceiling finishes
Wooden artefacts

4.5 Industrial Applications

Timber is also used in the manufacture of:

Plywood
Veneers
Block boards
Particle boards
Hardboards
Packing cases
Railway sleepers
Poles

Timber in Building Construction

5. Classification of Trees

Trees are broadly classified into two main categories:

Exogenous trees
Endogenous trees

5.1 Exogenous Trees

Exogenous trees grow outward by adding new layers of wood around the existing stem.

The growth takes place through a layer called the cambium.

Examples include:

Teak
Sal
Deodar
Pine
Fir
Oak
Sheesham

The wood obtained from exogenous trees is commonly used as timber for construction.

Annual Rings

The growth of an exogenous tree generally produces annual rings. Each ring represents approximately one year of growth.

Annual rings can provide information about:

Age of the tree
Rate of growth
Quality of timber
Environmental conditions during growth

Wide annual rings generally indicate rapid growth, while narrow rings indicate slower growth.

5.2 Endogenous Trees

Endogenous trees grow mainly from the inside. Their fibres are arranged differently from those of exogenous trees.

Examples include:

Bamboo
Palm
Coconut
Sugarcane

Endogenous trees generally do not produce annual rings in the same manner as exogenous trees.

Bamboo is widely used for:

Temporary structures
Scaffolding
Rural construction
Furniture
Decorative work
Lightweight construction

Timber in Building Construction

6. Classification Based on the Mode of Growth

Exogenous trees are further classified into:

Coniferous trees
Deciduous trees

Timber in Building Construction

6.1 Coniferous Trees

Coniferous trees are generally evergreen and have needle-like leaves. They usually produce softwood.

Examples include:

Pine
Fir
Deodar
Spruce
Cedar

Characteristics

Generally straight and tall
Usually evergreen
Produce softwood
Have relatively simple grain structure
Often grow rapidly
Commonly used for construction and packaging

6.2 Deciduous Trees

Deciduous trees generally shed their leaves during a particular season. They usually produce hardwood.

Examples include:

Teak
Sal
Oak
Sheesham
Mahogany
Walnut

Characteristics

Usually shed leaves seasonally
Produce hardwood
Generally denser than softwood
Often have complex grain patterns
Commonly used for furniture and high-quality construction

Timber in Building Construction

7. Softwood and Hardwood

Basis	Softwood	Hardwood
Source	Generally obtained from coniferous trees	Generally obtained from deciduous trees
Growth	Usually faster	Usually slower
Density	Generally lower	Generally higher
Grain	Usually simple	Often complex
Cost	Usually less expensive	Generally more expensive
Examples	Pine, fir, deodar	Teak, sal, oak, sheesham
Uses	Packaging, temporary work, light construction	Furniture, doors, flooring, structural work

The terms softwood and hardwood indicate the general nature of the wood. They do not always describe the actual hardness of every species.

8. Classification of Timber

Timber may be classified according to:

Botanical source
Physical properties
Durability
Strength
Weight
Use
Quality
Method of processing

Common classifications include:

8.1 Softwood Timber

Obtained mainly from coniferous trees.

Examples:

Pine
Fir
Deodar
Spruce

8.2 Hardwood Timber

Obtained mainly from deciduous trees.

Examples:

Teak
Sal
Oak
Sheesham
Mahogany

8.3 Natural Timber

Natural timber is obtained directly from trees and is used after processes such as:

Sawing
Seasoning
Preservation
Planing

8.4 Industrial Timber

Industrial timber is manufactured by processing wood into boards, panels, sheets, or other engineered products.

Examples include:

Plywood
Veneer
Hardboard
Particle board
Block board

Timber in Building Construction

9. Structure of a Tree

A cross-section of a tree trunk consists of several important parts.

9.1 Pith

The pith is the central and innermost portion of the tree stem.

It is generally soft and may contain cellular material.

9.2 Heartwood

Heartwood is the central, older, and usually darker portion of the tree.

Characteristics

Generally stronger than sapwood
More durable
Less permeable
Usually darker in colour
Provides structural support to the tree

Heartwood is commonly preferred for high-quality construction timber.

9.3 Sapwood

Sapwood is the outer portion of the wood located between the heartwood and cambium.

Functions

Conducts water and minerals
Stores food materials
Supports the growing tree

Sapwood is generally lighter in colour and less durable than heartwood.

9.4 Cambium Layer

The cambium is a thin layer of living cells located between the sapwood and inner bark.

It produces:

New wood toward the inside
New bark toward the outside

The cambium is responsible for the outward growth of the tree.

9.5 Inner Bark

The inner bark carries food prepared by the leaves to different parts of the tree.

9.6 Outer Bark

The outer bark protects the tree against:

Physical damage
Insects
Fungal attack
Excessive moisture loss
Temperature variations

9.7 Medullary Rays

Medullary rays extend radially from the pith toward the bark.

Their functions include:

Transporting food materials
Storing nutrients
Providing lateral support

9.8 Annual Rings

Annual rings are concentric rings formed due to seasonal growth.

They indicate:

Approximate age of the tree
Growth rate
Variations in climatic conditions

Timber in Building Construction

10. Processing of Timber

The main stages in the processing of timber are:

Felling
Conversion or sawing
Seasoning
Preservation

10.1 Felling

Felling is the process of cutting down a tree.

Trees are generally felled when they have reached suitable maturity and when the moisture content is comparatively low.

After felling, branches and bark may be removed before the trunk is converted into usable sections.

10.2 Conversion or Sawing

Conversion is the process of cutting a log into planks, boards, sections, or other required shapes.

The method of sawing affects:

Strength
Appearance
Shrinkage
Warping
Durability
Cost

Timber in Building Construction

11. Methods of Sawing

The main methods of sawing are:

Ordinary or flat sawing
Quarter sawing
Radial or rift sawing
Tangential sawing

11.1 Ordinary or Flat Sawing

In ordinary sawing, the log is cut into parallel boards with comparatively less wastage.

Advantages

Economical
Produces wider boards
Requires less time
Suitable for general construction

Disadvantages

Greater possibility of warping
More visible shrinkage
Less stable than quarter-sawn timber

11.2 Quarter Sawing

In quarter sawing, the log is first divided into quarters. Each quarter is then sawn into boards.

Advantages

Better dimensional stability
Less warping
Attractive grain pattern
Suitable for flooring and furniture

Disadvantages

More wastage
More expensive
Requires more time

Timber in Building Construction

11.3 Radial or Rift Sawing

In radial sawing, the boards are cut approximately along the radius of the log.

Advantages

Good dimensional stability
Less distortion
Suitable for high-quality work
Produces uniform grain

Disadvantages

More wastage
Higher cost
Requires skilled processing

11.4 Tangential Sawing

In tangential sawing, the boards are cut tangentially to the annual rings.

Characteristics

Produces attractive grain patterns
May result in greater shrinkage
More likely to warp
Commonly used for decorative work

12. Seasoning of Timber

Seasoning is the process of reducing the moisture content of freshly felled timber to a suitable level before use.

The main purpose of seasoning is to improve the quality and performance of timber.

12.1 Objectives of Seasoning

Seasoning helps to:

Reduce moisture content
Increase strength
Improve durability
Reduce shrinkage
Reduce warping
Prevent fungal attack
Improve workability
Reduce weight
Improve painting and polishing
Increase dimensional stability

Unseasoned timber may shrink, crack, twist, or warp after being used in construction.

Timber in Building Construction

13. Methods of Seasoning

Seasoning methods are broadly divided into:

Natural seasoning
Artificial seasoning

Natural seasoning includes air seasoning and water seasoning.

Artificial seasoning includes boiling, kiln seasoning, chemical seasoning, and electrical seasoning.

13.1 Air Seasoning

Air seasoning is the process of drying timber by exposing it to natural air circulation.

Timber boards are stacked in layers with spaces between them to allow air movement.

Procedure

Timber is cut into suitable boards.
Boards are stacked above ground level.
Small spacers are placed between the layers.
The stack is protected from direct rain and excessive sunlight.
Air is allowed to circulate around the boards.
Timber is left to dry gradually.

Advantages

Simple method
Economical
Requires less equipment
Suitable for large timber sections

Disadvantages

Requires considerable time
Depends on climatic conditions
Moisture content cannot be controlled precisely
May cause surface defects if drying is not uniform

13.2 Water Seasoning

Water seasoning involves placing timber in running water for a certain period.

The sap and soluble materials are removed from the timber. The timber is then dried in air.

Advantages

Removes sap
Reduces the tendency of timber to crack
May improve durability

Disadvantages

Requires a continuous water source
Timber may lose some strength
The process takes considerable time
Requires further drying after water treatment

Timber in Building Construction

14. Artificial Seasoning

Artificial seasoning is carried out under controlled conditions using equipment or special treatments.

It is faster and more reliable than natural seasoning.

14.1 Boiling Seasoning

In boiling seasoning, timber is immersed in boiling water for a specified period.

After boiling, the timber is dried under controlled conditions.

Advantages

Reduces seasoning time
Removes soluble substances
Helps reduce certain defects

Disadvantages

Requires considerable fuel
Not suitable for every type of timber
Requires additional drying

14.2 Kiln Seasoning

Kiln seasoning is carried out by placing timber inside a chamber called a kiln.

Temperature, humidity, and air circulation are controlled inside the kiln.

Advantages

Fast process
Controlled moisture reduction
Produces uniform quality
Suitable for large-scale production
Reduces the risk of fungal attack

Disadvantages

Expensive equipment
Requires skilled operation
Improper control may cause cracks and warping

14.3 Chemical Seasoning

In chemical seasoning, timber is treated with suitable chemicals that help remove moisture or accelerate drying.

Advantages

Can reduce drying time
May improve resistance to decay
Useful for selected timber products

Disadvantages

Chemicals may be costly
Requires proper handling
Not suitable for all applications

14.4 Electrical Seasoning

Electrical seasoning uses high-frequency electrical energy to heat and dry timber.

Advantages

Rapid process
Can be used for certain high-value timber products
Moisture can be controlled

Disadvantages

High operating cost
Requires specialized equipment
Not commonly used for ordinary construction timber

Timber in Building Construction

15. Preservation of Timber

Preservation is the process of treating timber with suitable substances to protect it against deterioration.

Preservation increases the service life of timber.

15.1 Causes of Timber Deterioration

Timber may deteriorate due to:

Fungal attack
Insects
Termites
Moisture
Fire
Weathering
Mechanical damage
Improper seasoning

15.2 Requirements of a Good Preservative

A good timber preservative should:

Be effective against fungi and insects
Penetrate into the timber
Remain effective for a long period
Not damage the timber
Not produce an unpleasant odour
Be economical
Be safe to handle when used correctly
Not interfere with painting or polishing
Resist washing out by water

Timber in Building Construction

16. Common Timber Preservatives

Common preservatives include:

Coal tar
Creosote
Solignum
Chemical salts
ASCU solution

16.1 Coal Tar

Coal tar is a dark, thick substance obtained during the manufacture of coal gas and coke.

It is applied to timber to protect it from:

Moisture
Fungal attack
Insects

Limitations

Dark in colour
Produces an unpleasant smell
Difficult to paint over
Generally unsuitable for visible interior surfaces

16.2 Creosote

Creosote is an oily preservative commonly used for timber exposed to outdoor conditions.

It is used for:

Railway sleepers
Poles
Fencing posts
Bridges
Outdoor structural timber

Creosote provides good resistance against decay and insects.

16.3 Solignum

Solignum is a proprietary timber preservative used to protect wood from insects and fungal attack.

It is commonly used for:

Doors
Windows
Roof timber
Furniture
Interior and exterior woodwork

16.4 Chemical Salts

Water-soluble chemical salts are used for preserving timber.

They may be applied through:

Brushing
Spraying
Dipping
Pressure treatment

Chemical salts are effective against certain insects and fungi.

16.5 ASCU Solution

ASCU is a chemical preservative solution used for protecting timber against decay and insect attack.

It is generally applied by brushing, spraying, or pressure treatment depending on the requirement.

Timber in Building Construction

17. Defects in Timber

Defects are undesirable features that reduce the strength, durability, appearance, or usefulness of timber.

Defects may occur due to:

Abnormal growth
Improper seasoning
Fungal attack
Insect attack
Defective conversion
Improper storage

Timber in Building Construction

18. Defects Due to Abnormal Growth

Important defects caused by abnormal growth include:

Shakes
Rind galls
Knots
Twisted fibres
Foxiness

18.1 Shakes

Shakes are cracks or separations that occur in timber, usually along the annual rings or in the radial direction.

They may develop due to:

Wind pressure
Frost
Excessive heat
Unequal growth
Internal stresses

Shakes reduce the strength and durability of timber.

18.2 Rind Galls

A rind gall is an abnormal swelling or growth on the trunk of a tree.

It may be caused by:

Injury
Insect attack
Fungal infection
Abnormal growth

Timber containing rind galls may have irregular grain and reduced strength.

18.3 Knots

Knots are portions of branches embedded in the trunk of a tree.

Types of Knots

Live knots
Dead knots
Loose knots
Encased knots

Knots may:

Disturb the grain
Reduce strength
Affect appearance
Cause difficulties during sawing and working

18.4 Twisted Fibres

Twisted fibres occur when the fibres of the tree do not grow parallel to the axis of the trunk.

Effects

Reduce strength
Cause difficulty in sawing
Increase warping
Reduce the quality of timber

18.5 Foxiness

Foxiness is a reddish or brownish discoloration in timber caused by abnormal growth or fungal activity.

It may indicate deterioration and reduced quality.

Timber in Building Construction

19. Defects Due to Seasoning

Improper or rapid seasoning may cause:

Bow
Cup
Twist
Warp
Checks
Splits
Cracks

19.1 Bow

Bow is the curvature of a board along its length.

The board bends like an arc when viewed from the side.

19.2 Cup

Cup is the curvature of a board across its width.

The edges of the board may rise or fall relative to the centre.

19.3 Twist

Twist occurs when the four corners of a board are not in the same plane.

It may be caused by:

Unequal drying
Irregular grain
Improper stacking

19.4 Warp

Warp is a general term used for undesirable distortion in timber.

It may include:

Bow
Cup
Twist
Crook

Warped timber is difficult to use in construction and furniture work.

Timber in Building Construction

20. Defects Due to Fungal Attack

Fungal attack generally occurs when timber contains excessive moisture and is exposed to suitable temperature and air conditions.

The two common fungal defects are:

Dry rot
Wet rot

20.1 Dry Rot

Dry rot is caused by fungi that attack timber under conditions of insufficient ventilation and moisture.

Effects

Timber becomes dry and brittle
Wood loses strength
Cracks develop
Timber may break into small pieces
A characteristic fungal smell may be present

20.2 Wet Rot

Wet rot occurs when timber remains continuously damp or wet.

Effects

Timber becomes soft
Colour changes
Strength decreases
Wood may become spongy
Decay progresses in damp conditions

Prevention of Fungal Attack

Fungal attack can be reduced by:

Proper seasoning
Adequate ventilation
Preventing water accumulation
Applying preservatives
Keeping timber above ground level
Repairing leakage and dampness

Timber in Building Construction

21. Industrial Timber

Industrial timber is manufactured by processing small pieces, thin layers, fibres, or particles of wood into useful boards and panels.

Industrial timber is developed to:

Reduce wastage
Improve dimensional stability
Produce large sheets
Provide uniform quality
Make efficient use of wood resources

Common types include:

Veneer
Plywood
Hardboard
Particle board
Block board

Timber in Building Construction

22. Veneer

Veneer is a thin sheet of wood obtained by slicing or peeling a log.

It is generally used as a surface layer over another material.

Uses

Furniture
Decorative panels
Doors
Cabinets
Wall panelling
Interior finishes

Advantages

Attractive appearance
Economical use of high-quality wood
Lightweight
Suitable for decorative work

Timber in Building Construction

23. Plywood

Plywood is a manufactured board made by bonding thin layers of wood called veneers.

The direction of the grain in successive layers is generally arranged at right angles to each other.

Characteristics

Strong and stable
Less likely to split
Available in large sheets
Suitable for furniture and construction
Better dimensional stability than ordinary wood boards

Uses

Plywood is used for:

Doors
Furniture
Cabinets
Partitions
Roof and wall panels
Formwork
Interior finishes
Packaging

Timber in Building Construction

24. Hardboard

Hardboard is a dense board manufactured from wood fibres compressed under heat and pressure.

It is generally smooth and uniform.

Uses

Furniture backing
Wall panelling
Door panels
Ceiling panels
Cabinet shutters
Partition boards

General Characteristics

Dense
Smooth surface
Uniform thickness
Economical
Available in different thicknesses

Timber in Building Construction

25. Particle Board or Chipboard

Particle board is manufactured by bonding wood particles, chips, or sawdust with a suitable adhesive under heat and pressure.

Uses

Furniture
Shelves
Cabinets
Tables
Partitions
Interior panels

Advantages

Makes use of wood waste
Economical
Available in large sheets
Uniform in appearance

Limitations

Lower resistance to moisture
Edges may be weak
May swell when exposed to water
Generally less durable than plywood

26. Block Board

Block board is made by placing strips or blocks of wood between layers of veneer and bonding them together.

Characteristics

Lightweight
Comparatively strong
Good dimensional stability
Suitable for large panels

Uses

Doors
Tables
Shelves
Partitions
Furniture
Interior panels

Timber in Building Construction

27. Comparison of Industrial Timber Products

Product	Main Material	General Use
Veneer	Thin layer of natural wood	Decorative surfaces
Plywood	Thin wood veneers	Furniture, doors, construction
Hardboard	Compressed wood fibres	Panels, furniture backing
Particle board	Wood particles and adhesive	Economical furniture
Block board	Wood strips and veneers	Doors, tables, partitions

28. Important Points for Revision

Timber is wood suitable for construction and engineering purposes.
Freshly felled wood is called green timber.
Exogenous trees grow outward and generally produce annual rings.
Endogenous trees grow from the inside and include bamboo and palm.
Coniferous trees generally produce softwood.
Deciduous trees generally produce hardwood.
Heartwood is the older and more durable inner portion of the tree.
Sapwood is the outer living portion that conducts water and stores food.
Cambium is responsible for the growth of new wood and bark.
Seasoning reduces the moisture content of timber.
Air seasoning is economical but time-consuming.
Kiln seasoning is faster and more controlled.
Preservation protects timber from insects, fungi, and moisture.
Shakes, knots, rind galls, and twisted fibres are defects due to abnormal growth.
Bow, cup, twist, and warp are seasoning defects.
Dry rot and wet rot are caused by fungal attack.
Plywood is made by bonding thin layers of veneer.
Particle board is made from wood particles and adhesive.
Block board is made from wood strips and veneers.

Timber in Building Construction

29. Short Answer Questions

What is timber?
What is green timber?
Define seasoning.
What is the purpose of seasoning?
What are exogenous trees?
What are endogenous trees?
Give two examples of coniferous trees.
Give two examples of deciduous trees.
What is heartwood?
What is sapwood?
What is the function of cambium?
What are annual rings?
What is ordinary sawing?
What is quarter sawing?
Define preservation of timber.
Name two timber preservatives.
What are knots?
What is bow in timber?
What is dry rot?
What is plywood?

30. Long Answer Questions

Explain the advantages and applications of timber in building construction.
Describe the classification of trees with suitable examples.
Differentiate between softwood and hardwood.
Explain the structure of a tree with a neat labelled diagram.
Describe the various stages involved in timber processing.
Explain the different methods of sawing timber.
Define seasoning and explain its objectives.
Describe air seasoning and water seasoning.
Explain the different methods of artificial seasoning.
What is timber preservation? Explain the requirements of a good preservative.
Describe the defects caused by abnormal growth in timber.
Explain the different defects caused by improper seasoning.
Describe dry rot and wet rot.
What is industrial timber? Explain its different types.
Explain the manufacturing process, characteristics, and uses of plywood.

Timber in Building Construction

31. Conclusion

Timber is an important natural construction material because of its strength, light weight, workability, appearance, and insulating properties. However, its performance depends greatly on proper selection, conversion, seasoning, preservation, and storage.

Understanding the structure of trees, methods of sawing, seasoning processes, defects, and industrial timber products is essential for the effective use of timber in building construction and interior design.

Useful link for preparation of competitive examinations:

Essential Assistant Director DDA MCQs for Planning Issues

10 Essential MCQs: DDA Assistant Director Planning Mock Test (Post Code 04) – ArchiTech Planner

External References

Students may refer to the following resources for additional information on timber, wood properties, forest products, and construction materials: