RSJ beams are a vital part of many building projects. You’ll find them in extensions, knock-throughs, and large-scale builds. They hold up the weight above when a wall or support is removed. They keep everything safe and sound. But knowing the right RSJ size to use isn’t always clear.

This blog explains what different RSJ sizes are for and why it matters to choose the right one. Picking wisely will make your build smoother, safer, and more cost-efficient.

Not All RSJs Do the Same Job

RSJ beams come in many shapes and sizes. Each is made for a certain job. Some are small and light. Others are large and heavy. Choosing the wrong one can lead to big problems. It may not hold the load. Or it might be bigger and costlier than needed.

Smaller beams like 152x89mm are often used for door openings. They’re common in home projects when a wall is removed between rooms. These beams are easy to handle and quick to fit. They don’t take up much headroom and can usually be installed without heavy machinery.

Medium RSJ sizes, such as 203x102mm, work well for wider spans. If you’re adding large windows or bifold doors, these are a better fit. They can take on more weight without being too bulky. They’re also popular in ground floor extensions and open-plan kitchen layouts.

Larger beams- 254x146mm and above- are made for big jobs. Think loft conversions, upper floor supports, or commercial builds. These RSJs carry serious weight and often need lifting gear to install. They may also need padstones or steel columns to transfer the load safely.

Think About Span, Load, and Where It Goes

To pick the right RSJ beam size, you need to think about three things:

• How wide is the gap it must cross?
• How much weight does it hold?
• And where will it sit?

An engineer will give you the final answer. Still, it’s helpful to know the basics. A small gap with a light load needs a small beam. A large open space with heavy weight needs a large one. You should also consider ceiling height, access for delivery, and building regulations.

Need help figuring this out? You can get a FREE, no-obligation quote today. We’re happy to guide you.

Practical Things to Plan For

Big beams take more effort. You might need a crane or lift to get it into place. You may also need to check delivery access to your site. Getting your beam cut to the right size before delivery can save time and money.

We offer a full range of RSJ beams in all sizes. All meet UK standards and are ready to use. Each section is measured and cut to fit, with reliable lead times and expert support.

Get the Right Beam, First Time

The right RSJ beam sizes makes your build faster, safer, and smoother. Using the wrong one can cost you in time, stress, and rework. 

Get in touch here for expert help from start to finish.