Determining what size timber for internal stud wall is the foundational decision that dictates the structural integrity, spatial efficiency, and build quality of any modern partition. The standard configuration relies on timber that is both resilient enough to bear the load of the structure above and light enough to allow for swift, precise installation. Getting this selection wrong can lead to walls that are prone to bowing, difficulty in hanging fixtures, or an inefficient use of materials, impacting both the budget and the final aesthetic of the space.
The Industry Standard: 75x50mm (3x2)
For the vast majority of domestic interior partitions in the United Kingdom and many other regions, the go-to specification is 75mm x 50mm (approximately 3 inches by 2 inches), typically referred to as a "three-by-two" stud. This dimension strikes an optimal balance between strength and practicality, providing sufficient vertical rigidity to support regular plasterboard cladding and any upper-floor loads. The 75mm depth offers a substantial surface for fixing, ensuring screws have enough bite to hold the materials securely, while the 50mm width maintains a slim profile that maximises usable floor space within the room.
Spacing and Layout
Simply choosing the timber is only half the battle; proper spacing is equally critical for performance. Studs are generally installed on 400mm centres, measured from the centre of one vertical member to the next. This spacing is engineered to align perfectly with the width of a full sheet of plasterboard (typically 1200mm wide). When the boards are laid in a staggered pattern—often starting with a full sheet at one end—every vertical joint falls securely onto a stud, creating a continuous load path and eliminating the need for internal noggins in standard height partitions.
When to Consider 100x50mm (4x2)
While 75x50mm is the norm, there are specific scenarios where stepping up to 100mm x 50mm (4x2) timber is not just beneficial but necessary. If the partition is acting as a load-bearing element, supporting significant weight from a heavy timber floor or an upper structure, the additional depth provides crucial extra strength. Furthermore, for very long unfettered wall runs exceeding three metres, the increased section helps resist sag and bounce, ensuring the wall remains perfectly straight and true over distance.
Acoustic and Thermal Considerations
The density and mass of 100mm timber contribute to better sound insulation properties compared to its smaller counterpart. For walls separating living spaces from bedrooms or home offices, this extra mass helps dampen airborne noise. Additionally, the larger cavity depth allows for thicker layers of mineral wool insulation, which significantly improves the wall's thermal performance (U-value). This is a key consideration for renovations aiming to meet modern energy efficiency standards or for creating comfortable, temperature-stable environments.
| Timber Size (mm) | Typical Use Case | Stud Spacing | Best For |
|---|---|---|---|
| 75 x 50 | Standard Internal Partition | 400mm Centre | Drywall, quick builds, standard rooms |
| 100 x 50 | Long Runs or Load Bearing | 400mm Centre | Structural walls, insulation, soundproofing |
The Critical Role of CLS and Shiplap
When sourcing your timber, you will encounter two primary grades: CLS (Canadian Lumber Standard) and Shiplap. CLS timber is machine-planed to be smooth, straight, and dimensionally accurate, making it the premium choice for internal work. Its clean edges reduce waste when cutting and its consistent quality ensures a flawless finish behind plasterboard. Shiplap, with its overlapping edges, is primarily used for external work or internal structures where the wall will be left exposed, as the interlocking profile can create an uneven surface that is difficult to plaster over smoothly.
Foundation and Fixing Points
Regardless of the timber size selected, the foundation of the wall is paramount. The bottom plate, usually a pressure-treated 75x100mm (3x4) or 150x50mm (6x2), sits on the floor and acts as a damp proof membrane and fixing point. The top plate, matching the stud size, is used to secure the structure to the ceiling. At the very least, fixing points should be placed at every stud along the bottom plate, at the top, and at any point where the wall intersects with another. For 100x50 studs, using 50mm or 63mm screws ensures the fastener has enough thread to grip the timber securely without splitting the wood.
Ultimately, the decision on what size timber for internal stud wall hinges on a careful assessment of the wall's purpose, span, and environmental needs. By adhering to the standard 75x50mm for typical use and reserving the 100x50mm for demanding structural or acoustic requirements, you ensure a build that is both efficient and enduring, providing a solid, reliable frame for the finishes that will define the room.
