Steel or Timber? Choosing the Right Beam for Your Extension

Beam Designs
May 28
2 min read

When you're planning a home extension, one of the most important decisions is hidden in the structure: what type of beam will support your new space? While most people assume steel is the only option, that’s not always the case. Depending on the project, timber beams can be a viable – and cost-effective – alternative.

At Beam Designs, we help homeowners across the UK, especially in London and Manchester, understand their structural beam options through clear, compliant extension beam calculations.

When Steel Beams Make Sense

Steel beams (often RSJs or I-beams) are commonly used to support large openings in rear or side extensions. They're strong, compact, and ideal when head height is limited - a common issue in urban homes. If you’re removing a load-bearing wall or spanning a wide area, steel usually wins on strength-to-size ratio. It also performs better in damp or exposed environments.

When Timber Beams Can Work

In single-storey extensions with modest spans and loads, timber beams can be used safely and legally - provided the design complies with Building Regulations. Glulam (glued laminated timber) beams are especially strong and can look great left exposed in open-plan kitchens. They’re lighter and easier to work with than steel, making them a smart choice in tight-access properties.

How Structural Calculations Help You Decide

There’s no guesswork here. A structural engineer runs calculations based on span, load, and support conditions to recommend the best material and beam size for your project. Overdesigning leads to unnecessary costs. Underspecifying? That’s a safety risk. Our job is to get it just right.

Need calculations for your extension? We offer clear, affordable design packages tailored to your home – whether you're building in Birmingham or removing a timber beam load-bearing wall in East London.

Join the countless satisfied clients who have entrusted Beam Designs with their structural engineering needs.