7th Dec 2022 -

5x2 timber can function as both an all-purpose construction beam, and for joist and stud work. In this overview from Building Materials Nationwide, we’ll cover the accurate UK sizing for 5x2 timber, the different types on sale, and some of the key uses within a building project.

How Will 5x2 Timber Be Sold in the UK?

5x2 timber will rarely be listed as an option when looking for building supplies in the UK. This is because businesses are mandated to use metric measurements when selling products, usually mm in the case of timber. When shopping for 5x2 timber therefore you should be looking for a 125mm x 50mm beam, which is the closest equivalent sold within the UK. This is called the nominal size, so it’s worth bearing in mind that most timber will actually be smaller than this by the time you purchase it.

Nominal Sizes vs. Actual Sizes

The nominal size, or listed size, of a piece of timber is the size it was rough sawn to from a felled tree. This is known as green timber, due to its high water content. While there are several practical uses for green timber, it will naturally shrink over time making it unsuited for most construction tasks. Kiln-drying is the common process to make timber ready for sale, reducing the moisture content to below 20%, which will also have the effect of shrinking the timber. Another process that will reduce the size of the timber is planing, which is effectively sanding one or more faces of rough sawn timber in order to make it smooth and attractive. Unless specifically buying green timber, the actual size of a 5x2 timber beam will be around 114mm x 38mm.

What Lengths of 5x2 Timber Are Sold?

Timber is typically sold in lengths that go up in 60cm increments. For instance, within our C24 treated 5x2 timber we stock the lengths 2.4m, 3.6m, 4.2m, and 4.8m.

What Are my Options For 5x2 Timber?

When shopping for 5x2 timber you’ll see several options available, with finishes and strength grades that can make them more suitable for specific uses.

C16 and C24 Graded 5x2 Timber

When looking to use timber within any structural or load-bearing capacity, it’s important to only use wood that has been specifically strength graded. Within the UK, C16 and C24 are the most common gradings of softwood timber available, with C24 the stronger of the two. This rating means that a piece of timber has been machine tested for strength and consistency, assuring that it can be safely used within a project. When purchasing 5x2 timber for construction purposes, you should be looking to buy C16 or C24 wood.

Treated 5x2 Timber

Softwood timber is prone to rot and decay when exposed to water, either from rain, damp, or moisture within the soil. Pressure-treated timber, sometimes called tanalised timber, is a great solution to this, as it has been thoroughly coated with preservatives, giving it both moisture and insect resistance. Wood burrowing insects can be a threat to timber, both visually and structurally. When using 5x2 timber externally, or in an area at risk of moisture, you should opt for a treated model.

How Can 5x2 Timber be Used in a Building Project?

Alongside general construction usage, there are a couple of specific areas where 5x2 timber is commonly used.


5x2 timber can be used for joists throughout a building project, within the roof, floor, or walls. In situations like floor joists where there will be weight placed on them opting for strength graded 5x2 timber beams would be a good idea. In areas with a risk of moisture, such as internal walls, tanalised timber can ensure long-lasting performance.

Stud Walls

Within a stud wall, 5x2 timber can be used for top plates, bottom plates, noggins, and studs. These sizes will be sturdy enough to build a solid internal wall, covered with plasterboards and decorated as you see fit. Within a non-load-bearing stud wall using strength graded timber is inessential, and you can also opt for rough sawn dried timber to further save money.

Quality Timber Delivered Nationwide

Building Materials Nationwide offers a range of timber and joinery supplies for sale, delivered across the UK at competitive prices. We work with building companies, contractors, and skilled DIYers alike, streamlining the process of sourcing products. We stock 5x2 timber in treated and structural finishes, alongside CLS timber and PSE timber. For our customers within the building industry, we also offer trade accounts, gaining them access to our full network of suppliers, our expedient delivery options, and the services of a dedicated account manager. Sign up for a trade account today.