What Is Carcassing Timber? A Complete Guide By Timber Experts 

From framing, to flooring, to decking, carcassing timber is your essential timber choice for all structural projects. In this expert guide, we’ll walk you through what carcassing timber is, its main uses, if it can be used externally, and answer all of your important questions. 

What is Carcassing Timber? 

Carcassing timber is vital for creating the skeletal structure of a building. It is primarily used for first-fixing applications, such as framing and joists, and can be made from both softwoods and hardwoods. Most carcassing timber will be used in load-bearing applications, which makes strength grading incredibly important, with most carcassing options in the UK being either C16 and C24. 

C16 and C24 timber are softwoods that have been kiln-dried to a moisture content below 20% and then pressure-graded. This makes them particularly strong and reliable choices for carcassing. C16 is the more affordable of the two as it has a lower strength grading and more imperfections compared with its stronger, higher-quality counterpart C24. Which strength grading is best for you will depend on your project’s specific needs. 

What Is Carcassing Timber Used For?

Carcassing timber is predominantly used for the structural framework of buildings. This timber is crucial in creating the skeleton of a building, providing essential support and stability. Its primary applications include: 

• Joists: Carcassing timber is used to create joists, providing a strong and stable horizontal structure for flooring and roofing. 
• Framing: This timber forms the framework for walls, doors, and windows, ensuring structural integrity and support throughout the construction. 
• Rafters: Carcassing timber is utilised in building rafters, which are essential for supporting the roof and distributing its weight evenly. 
• Stud Walls: It can be used to construct stud walls, which serve as internal partitions or support for exterior walls in a building. 
• Roof Battens: Carcassing timber is used in laying roof battens, which provide the overall stability of the roof. 
• Flooring: It can be used as a base for flooring, providing a secure foundation that ensures structural support and even weight distribution. 
• Other: Carcassing timber is very versatile, and can also be used in fencing, decking, palettes, and more. 

Most carcassing timber will not be visible in the finished project, meaning that any visual imperfections and a rough sawn appearance are both acceptable. However, if some elements are going to be visible in the final structure, like exposed beams, a higher quality timber like planed C24 would be the best choice. 

What Is Timber Grading? 

Timber strength grading is a process used to assess the structural capacity and quality of timber. This grading system ensures that timber meets specific strength and durability standards required for construction. Timber is typically graded visually or by machine. Visual grading involves inspecting the timber for defects such as knots, splits, and grain deviations. Machine grading uses mechanical stress to test the timber's strength. 

The most common grades are C16 and C24, with C24 offering greater levels of strength.It’s important to keep in mind that if you cut or thin the beam it will need to be regraded. 

The number grading refers to the minimum strength the wood beam can take per square millimetre. Any graded timber will have its rating stamped as certification. Below are the stress grading passing amounts for C16 and C24 timber decided by the British Standards BS 5268-2:

Is Carcassing Timber Treated? 

While you can source it untreated, most carcassing timber will have been kiln-dried to a moisture level below 20% and pressure-treated with chemicals. This process improves the strength and durability of the wood by making it more resistant to moisture, warping, cracking, and insect infestations. This will make sure the building’s structure is strong and long-lasting. 

If you are creating a structure without load-bearing requirements and where dampness is not a concern, untreated carcassing timber is available.  

What Sizes Does Carcassing Timber Come In? 

Carcassing timber comes in a wide range of sizes to meet the specific needs of any project. At Cover Builders Merchants, we stock these dimensions: 

• Between 22 x 100mm and 22 x 225mm 
• Between 38 x 50mm and 38 x 225mm 
• Between 47 x 50mm and 47 x 250mm
• Between 75 x 100mm and 75 x 225mm 
• Between 100 x 100mm and 100 x 150mm 

If you need a certain size, we are always happy to provide additional lengths and sizes than what you see here. 

Can Carcassing Timber Be Used Outdoors? 

Carcassing timber can be used for external projects like decking and fencing, provided it is appropriately treated. Treating the timber protects it from weather conditions, rot, decay, and insect infestation, so it is suitable for long-lasting outdoor use. 

How Should Carcassing Timber Be Stored? 

Carcassing timber should be stored in a dry, well-ventilated place to keep it in optimal condition and prevent decay. Proper ventilation ensures moisture does not accumulate, which can lead to mould and rot. It's important to stack the timber flat and evenly to prevent warping and maintain its structural integrity. It’s crucial to avoid placing the timber directly on the ground, so use supports to keep it elevated. Covering the timber with a protective sheet can also shield it from direct exposure to rain while still allowing airflow. 

Find Top-Quality Timber For Your Next Project

Whatever your next project, we have an extensive selection of high-quality Structural Timber & Carcassing for you to explore. 

At Covers Builders Merchants, you can rely on expertise earned from over 175 years of experience in the industry. We pride ourselves on our commitment to top-quality products and exceptional customer service. Visit your nearest Covers depot, to experience the difference shopping at a family-run business makes.