What Size Timber Should I Use for Studwork?

For most internal stud walls in UK homes, 38mm x 63mm CLS timber, roughly 3x2 in trade terms, or 38mm x 89mm CLS timber, roughly 4x2 in trade terms, is commonly used. As a simple guide, 38mm x 63mm is often suitable for lightweight internal partitions, while 38mm x 89mm is usually the better choice when you want a stronger wall, more room for insulation, or space for services such as pipework and cables.

The right timber size depends on what the wall is being used for, whether it is load-bearing, the wall height, plasterboard type, insulation requirements, and whether anything heavy will be fixed to it later.

What is the best timber size for a stud wall?

The most common timber sizes for studwork are:

• 38mm x 63mm CLS timber – a common choice for lightweight internal partition walls where space is limited.
• 38mm x 89mm CLS timber – often preferred for stronger partitions, taller walls, improved insulation depth and easier service runs.
• 75mm x 100mm timber – sometimes used where extra strength, depth or fixing space is needed.

For many domestic projects, 38mm x 63mm or 38mm x 89mm CLS will be the most practical starting point. Larger sections may be needed where the wall is taller, heavier, load-bearing or designed to support fixtures.

What does CLS timber mean?

CLS stands for Canadian Lumber Standard. In the UK, CLS timber is widely used for internal stud walls, partitions and framing because it is regularised, consistent in size and has eased edges that make it easier to handle.

CLS timber is popular for studwork because it is:

• Easy to work with
• Smooth and regularised
• Available in standard sizes
• Suitable for plasterboard framing
• Commonly stocked by UK timber merchants
• A practical choice for both trade and DIY partition walls

Should I use 38mm x 63mm or 38mm x 89mm timber for studwork?

Use 38mm x 63mm timber for simple lightweight internal partitions, and 38mm x 89mm timber where you want a sturdier wall or more space inside the cavity.

38mm x 63mm timber is usually suitable for:

• Simple room dividers
• Cupboard partitions
• Lightweight non-load-bearing walls
• Small domestic projects
• Areas where saving floor space matters

38mm x 89mm timber is usually better for:

• Taller stud walls
• Better sound or thermal insulation
• Walls carrying heavier plasterboard
• Walls with sockets, pipework or service voids
• Walls where shelves, cabinets or radiators may be fitted
• A more solid feel once boarded

The smaller size can help keep the wall slimmer, while the deeper section creates a more useful cavity and can make the finished partition feel more robust.

Is 3x2 or 4x2 better for stud walls?

In trade terms, studwork timber is often described as 3x2 or 4x2, but the actual finished sizes are usually smaller after machining has been finished. As a rough guide:

• 3x2 timber often refers to timber close to 38mm x 63mm.
• 4x2 timber often refers to timber close to 38mm x 89mm or 47mm x 100mm, depending on the product.

For a basic internal partition, 3x2 may be enough. For a more robust stud wall, 4x2 is often the better option. This is especially true if the wall needs insulation, sound reduction, services, shelving support or greater stiffness.

What spacing should timber studs be?

Timber studs are commonly spaced at 400mm centres, around 16in, or 600mm centres, around 24in, depending on the wall design and plasterboard being used. The phrase “centres” means the distance from the centre of one stud to the centre of the next. Common stud spacing includes:

• 400mm centres, around 16in, for a stronger wall and better board support.
• 450mm centres, around 18in, in some tiled rooms or where additional support is needed.
• 600mm centres, around 24in, where suitable for the plasterboard thickness and wall specification.

Closer spacing can be useful where heavier finishes are planned, where the wall needs to feel more solid, or where the chosen board type requires additional support.

What size timber should I use for a load-bearing stud wall?

If the wall is load-bearing, do not guess the timber size. Load-bearing stud walls should be designed or checked by a competent professional, such as a structural engineer, architect, builder or Building Control-approved designer.

A load-bearing wall may need:

• Larger timber sections
• Specific C16 or C24 structural grading
• Correct sole plates and head plates
• Extra studs around openings
• Lintels or beams
• Noggins or bracing
• Structural calculations

What size timber should I use for a bathroom stud wall?

For a bathroom stud wall, 38mm x 89mm CLS is often a sensible choice because it gives more room for plumbing, insulation and stronger board support. Bathrooms can also involve heavier wall finishes, especially if the wall will be tiled.

For bathrooms, consider:

• Moisture-resistant plasterboard or tile backer board
• Closer stud spacing where required
• Extra noggins for basin brackets, towel rails or cabinets
• Space for pipework
• Ventilation and moisture control
• Suitable fixings for heavy wall-mounted items

Where tiles, cabinets, basins or towel rails will be fitted, it is worth planning the timber layout before boarding so that there is enough support where the fixings will go.

What size timber should I use if I want insulation in the wall?

Use deeper studwork if you want more insulation inside the partition. A 38mm x 89mm stud gives more cavity depth than 38mm x 63mm, making it easier to fit acoustic or thermal insulation. This can be useful for:

• Bedrooms
• Bathrooms
• Home offices
• Utility rooms
• Garage conversions
• Separating noisy spaces
• Improving privacy between rooms

For internal sound reduction, the overall wall build-up matters as much as the stud size. Plasterboard type, insulation, board layers, gaps, sealing and installation quality all affect performance.

What timber grade should studwork be?

For most domestic studwork, CLS or structural softwood such as C16 is commonly used, depending on the application. If the wall is purely non-load-bearing, the key requirement is usually straight, stable, regularised timber suitable for framing. If the wall is load-bearing, the grade and size should follow the specification.

When buying studwork timber, check:

• Size
• Length
• Grade
• Moisture content
• Straightness
• Whether it is treated or untreated
• Whether it is suitable for internal use
• Whether it matches the project design

Regularised timber is usually easier to work with for stud walls because the sections are more consistent and the eased edges make handling and installation more comfortable.

Do I need treated timber for internal stud walls?

Most internal stud walls do not need treated timber if they are in dry, normal indoor conditions. Untreated CLS is commonly used for internal partitions.

Treated timber may be worth considering where there is a higher risk of moisture, such as:

• Garages
• Utility rooms
• Basements
• External-facing structures
• Areas near masonry
• Projects where the specification asks for treated timber

However, treatment does not make timber stronger. A treated piece of timber still needs to be the right size and grade for the job.

What size timber should I use around door openings?

Door openings need careful framing because they interrupt the standard stud layout. The exact timber size depends on the door lining, wall thickness, plasterboard and structural requirements.

For a typical internal doorway, you will usually need:

• Studs either side of the opening
• A head piece above the door
• Additional short studs where required
• Correct allowance for the door lining
• Enough wall depth for plasterboard and finish

If the opening is in a load-bearing wall, it may need a lintel or structural beam and should not be treated as a basic partition.

What is the finished thickness of a stud wall?

The finished wall thickness depends on the stud depth and the board used on each side. As a simple example:

• 38mm x 63mm studs with 12.5mm plasterboard each side create a wall around 88mm thick, around 3.5in.
• 38mm x 89mm studs with 12.5mm plasterboard each side create a wall around 114mm thick, around 4.5in.

This does not include skim coat, tile backer board, acoustic board, battens, service voids or wall finishes.

What size timber should I use for studwork?

For most standard internal stud walls, 38mm x 63mm CLS or 38mm x 89mm CLS will be the most practical choice. Choose 38mm x 63mm where the wall is lightweight and space-saving. Choose 38mm x 89mm where you want a stronger partition, better insulation depth or more room for services.

As a quick guide:

• Choose 38mm x 63mm CLS for lightweight internal partitions.
• Choose 38mm x 89mm CLS for stronger, more versatile stud walls.
• Choose larger structural timber where the wall is load-bearing or specially designed.
• Use 400mm or 600mm centres depending on board type and wall requirements.
• Use closer spacing where heavier finishes, such as tiles, are planned.
• Ask for professional advice if the wall is load-bearing or supports anything structural.

For most trade and DIY customers, the safest starting point is to choose a good-quality CLS or graded timber from a reliable timber merchant and match it to the project specification.