In the construction and architectural industry, the quality of each building material plays a vital role. Every building component must meet essential building standards to ensure safety and structural integrity after construction, thereby guaranteeing long-term performance. Timber is one of the major construction materials, playing a significant part in building design. Read this blog to understand what timber is, its classification, different timber tests and the IS codes governing them.
What is Timber?
Timber refers to wood that is suitable and prepared for construction and building purposes. When wood is processed into standard sizes such as beams, planks, or boards and attains the required strength and durability, it is termed timber (also known as lumber). Timber is primarily used for structural applications, including columns, beams, flooring, roofing, and formwork, where it must safely withstand loads and provide long-term stability.
Different Classifications of Timber
Timber classification is as follows:
- Softwood: It is derived from coniferous trees, like pine. These are affordable and have better workability, suitable for framing structures.
- Hardwood: It is derived from deciduous trees, like oak. These are pricey due to their durability and strength. Hardwood is known for its resistance to wear and tear, making it suitable for flooring and furniture. Also, hardwood is best suited for decorative purposes in architectural elements such as trim, mouldings, and panelling.
Properties of Good Quality Timber
The following are major properties of timber to consider as good quality:
- Strength: In construction projects, wood is used for structural purposes, such as beams, columns, and joists. Therefore, the wood should have high strength to resist considerable loads and stresses.
- Durability: The timber must be sufficiently durable to prevent decay, pest infestation, and other environmental factors such as moisture and temperature fluctuations. Timber with maximum durability can extend the lifespan of the structure.
- Toughness: As the structure might face dynamic forces, timber must be tough enough to absorb sudden shocks or impacts without sudden failure to avoid.
- Elasticity: Timber must have moderate elasticity to regain its shape after undergoing deformation, allowing it to flex under load without permanent deformation.
- Workability: The timber should be easy to handle, allowing for cutting to give it the required shape with a proper finish.
What are the Essential Tests on Timber?
The following are the major tests on timber that need to be conducted before using it in construction:
- Moisture content test
- Tensile strength test
- Compressive strength test
- Shear strength test
- Bending test
1. Moisture Content Test
The moisture content test determines the water content of wood. The moisture content test is used to forecast how timber will behave in a varying environment. This test will be conducted using a weighing machine and a drying oven, measuring scale following IS 2380 Part VI – 1977 and IS 1708.
The small timber sample (commonly 5cm x 5cm x 2.4cm) will be weighed, and it’s referred to as the initial weight. It will undergo a drying process in the oven until its weight remains constant. The moisture content of the timber sample can be calculated by subtracting the dry weight from the initial weight, dividing by the dry weight, and multiplying by 100. The agreeable moisture content range for timber generally varies from 12% to 15% for use in construction and manufacturing.
2. Tensile Strength Test
The tensile strength of wood or timber is used to identify its maximum strength and ability to withstand tensile loads.
This test will be conducted using a tensile tester that comes with a clamper featuring gripping jaws. The standard wooden sample will be prepared and gripped in the jaws. Based on testing standards (IS I 2380 (Part VI) – 1977), the load will be applied. Once the sample fails, the machine stops itself for over-travel protection. One can calculate tensile strength by dividing the maximum load by the cross-sectional area.
The acceptable tensile strength of wood for building use is as follows:
- Softwoods show tensile strengths varying from 30 MPa to 50 MPa, while hardwoods show 50 MPa to 100 MPa.
- For structural timber, a minimum tensile strength of 40 MPa is essential
3. Compressive Strength Test
The compressive strength test of timber or wood is used to determine its maximum ability to withstand crushing loads along the grain and across the grain.
Wood specimens of standard size (5cm x 5cm x 20cm) will be prepared and placed in a Universal Testing Machine with steel bearing plates, following IS 2380 code. The load will be applied parallel to the grain and across the grain until the specimen fails. The compressive strength is calculated by dividing the maximum load sustained before failure by the specimen’s cross-sectional area. The value of maximum compressive strength varies based on the tree species and quality; softwoods range roughly from 30 to 50 MPa, while hardwoods can exceed 50 MPa. Typical shear strength values for timber range from 6 MPa to 14 MPa, depending on species and quality.
4. Shear Strength Test
The shear strength test of timber is used to evaluate its ability to resist sliding failure along the grain, which is important to maintain the structural integrity in joints and beams. As per IS 1708, the specimen (standard size 5 cm x 5 cm x 6.25 cm or 2 cm x 2 cm x 3 cm) is prepared. One end will be notched to induce shear failure on a 5 cm x 5 cm face. The specimen is placed in a universal testing machine equipped with a shearing tool in the rig. A steady load is applied parallel to the grain at a rate of 0.4 mm/min until failure occurs. The maximum shear load is recorded. The shear strength of timber will be calculated by dividing the maximum shear load by the cross-sectional area. Typical shear strength values for timber range from 6 MPa to 14 MPa, depending on species and quality.
5. Bending Test of Timber
The bending test of timber is used to determine the modulus of rupture, and modulus of elasticity (which is its ability to carry bending loads). The test will use a wood sample (dimensions- 5 cm x 5 cm x 7.5 cm), a universal testing machine, and a vernier calliper. The sample will be simply supported on two rollers, and the distance between roller supports will be 24 times the sample thickness. A load will be applied at a constant rate at the central point until the sample fails to carry it. The maximum load and deflection data will be measured. The modulus of rupture and modulus of elasticity will be calculated using these data. This is performed to measure if the timber is safe to use as structural timber for bending stresses. A typical acceptable modulus of rupture would range from 40 MPa to 100 MPa, depending on timber species. Hardwoods generally have a higher value. The modulus of elasticity (MOE) values range from 7 GPa to 15 GPa, and indicate stiffness. Values may vary depending on the grain direction, moisture content, and quality of timber.
Indian Standards for Timber Testing
The following are Indian standards for timber testing:
- IS 1708 (Parts 1–18): It covers test methods for mechanical and physical properties, along with tensile strain, compressive strain, bending strain, shear strain, moisture content and density.
- IS 399: It gives classification guidelines for commercial timbers, helping in grading timber quality and suitability for different uses.
- IS 287: It offers recommendations on the seasoning of timber to achieve the desired moisture content and enhance durability.
- IS 2380: It specifies the methods of testing for wood particle boards and related lignocellulosic materials.
Applications of Tested Timber in Civil Engineering
The following table represents the application of timber based on its testing results:
| Application Area | Examples | Suitable Timber Properties | Why Testing Matters |
| Structural Frameworks | Beams, columns, trusses | • Bending and tensile strength• Good elasticity and load-bearing capacity | Ensures structural stability and prevents failure under load. |
| Building Components | Flooring, doors, windows, formwork | • Hardness and surface durability• Moisture resistance and dimensional stability | Improves finish, durability, and fit during construction. |
| Infrastructure Works | Bridge decks, railway sleepers, scaffolding | • High impact and shear strength• Resistance to decay and weathering | Provides safety under dynamic loads and extends service life. |
| Sustainability & Aesthetics | Used across all applications, including wardrobes | • Controlled moisture content• Verified density and defect-free quality | Promotes eco-friendly, long-lasting, and visually appealing construction. |
Conclusion
Timber testing is important to make sure you are using high-quality timber that is free from any defects and suitable for the construction. This way, you can maintain structural safety, longevity, and optimal performance in construction projects. The builder must conduct the above tests following the Indian standard codes for reliable material selection. This will help reduce material failures in different applications, from structural frameworks to decorative elements. Testified, high-quality wood enhances building integrity with sustainable construction practices.For premium-quality timber and other construction materials that meet industry standards, explore Brick & Bolt’s Building Materials Supply. Build with confidence, choose materials you can trust.