The Great Debate: Traditional Masonry or Modern Steel?

If you are planning a home extension in the UK, you are likely facing a common dilemma. Your builder suggests traditional brick and block because "that’s how it’s always been done." But your architect—or perhaps your own research—is pointing you toward a Steel Frame System (SFS).

While brick is familiar, the modern demand for open-plan living and energy efficiency is making steel the superior choice. But how do they actually compare?

Steel frame extension vs brick Bas Frames


Here is the honest breakdown of Brick vs. Steel for your single or double-storey extension.

1. Speed of Build: The Clear Winner

This is where the difference is most dramatic.

  • Brick: A traditional extension relies on wet trades. You have to wait for the mortar to dry, and if it rains (which it does, often), work stops. A typical brick shell can take 6–10 weeks to complete.

  • Steel: The frame is prefabricated off-site. Once delivered, it can be assembled remarkably fast. A stick build system—where individual steel members are assembled on-site—can often be erected and made watertight in just 1–2 weeks.

The Verdict: Steel wins. For homeowners living on-site during the build, weeks of saved disruption are priceless.

2. Wall Thickness & Internal Space

In London and urban areas where every square foot costs thousands of pounds, wall thickness matters.

  • Brick: To meet modern insulation standards (U-values), traditional brick walls need to be very thick (often 300mm+ cavity walls) to hold enough insulation.

  • Steel: Steel frames are stronger but thinner. High-performance insulation fits between the steel studs rather than just in a cavity.

The Verdict: Steel wins. You can gain significant internal floor space—sometimes enough for an extra kitchen cabinet or wider hallway—just by choosing a thinner steel profile.

3. Design Flexibility (The "Open Plan" Dream)

Do you want bi-fold doors spanning the entire back of your house?

  • Brick: Masonry is heavy. To support a wide opening, you will likely need to insert a heavy steel beam (RSJ) anyway, which complicates the brickwork.

  • Steel: The entire structure is the support. Steel frames are naturally designed to handle large spans and heavy loads without needing internal load-bearing walls.

The Verdict: Steel is the natural choice for modern, open-plan designs.

4. Cost: It’s Not Just About Materials

Many builders will tell you steel is more expensive. On paper, the material cost of steel is higher than a pallet of bricks. However, you must look at the total build cost:

  • Labor Savings: Because the frame goes up faster, you pay for fewer weeks of labor.

  • Foundation Savings: Steel is much lighter than brick. This often means you can use shallower, less expensive foundations.

  • Waste Savings: Steel is precise. There is no skip full of broken bricks and wasted cement at the end.

Summary: Which System is Right for You?

If you want a traditional cottage look and aren't in a rush, masonry is fine. But for 90% of modern extensions—especially those prioritizing speed, thermal warmth, and open space—steel is the smarter investment.

The most popular method for extensions is the Stick Build system. This allows the steel to be delivered in manageable pieces (perfect if you have no side entrance and materials need to go through the house) and assembled quickly in the garden.

Next Step: Curious about how a Stick Build system comes together? Check out the technical details and process at BAS Frames to see if it fits your project.

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