How We Handle Structural Alterations
Understanding RSJ beams, knock-throughs, and the process of safely removing load-bearing walls
What Is a Structural Knock-Through?
A knock-through (or structural alteration) involves removing a load-bearing wall to create open-plan living spaces. It's one of the most popular home improvements—but also one of the most complex. Here's what you need to know before you start knocking down walls.
Critical warning: Never remove a wall without professional assessment. Load-bearing walls support the weight of the floors and roof above. Remove one incorrectly, and you risk catastrophic structural failure. We've seen DIY disasters that cost £50,000+ to fix.
Understanding Different Structural Works
RSJ Steel Beam Installation
RSJ (Rolled Steel Joist) beams replace the load-bearing function of a removed wall. They're sized by a structural engineer based on the load they need to support—typically 152mm, 178mm, or 203mm deep.
Why steel? Steel is incredibly strong for its size. A 178mm RSJ can support the weight of an entire floor above, allowing you to create wide, open spaces without internal support.
Knock-Through (Open Plan Living)
The most common structural alteration: removing the wall between kitchen and dining room to create an open-plan space. This transforms cramped Victorian terraces into modern, light-filled homes.
Typical cost: £3,000-£6,000 including structural engineer, Building Control, RSJ, installation, and making good (plastering, decorating).
Underpinning & Foundation Work
When foundations have settled or subsided, underpinning strengthens them by extending the foundation depth. Common for Victorian properties with shallow foundations or where ground conditions have changed.
Signs you need it: Cracks wider than 5mm, doors/windows sticking, visible settlement, or cracks that widen over time.
Lintel Replacement & Reinforcement
Lintels support the load above windows and doors. Older properties often have timber lintels that rot over time. We replace them with steel or concrete lintels that last indefinitely.
Warning signs: Cracks above windows/doors, sagging brickwork, or visible timber decay. Don't ignore these—they can lead to major structural failure.
Our 6-Step Structural Alteration Process
Structural work requires careful planning, professional engineering, and Building Control approval. Here's how we ensure every project is safe, legal, and built to last:
Initial Structural Survey
We visit your property to assess the wall you want to remove. Is it load-bearing? What's above it (floor joists, walls, roof)? What's the construction type (brick, block, timber frame)? We take measurements, photos, and notes.
Key question: How do you know if a wall is load-bearing? Generally, walls running perpendicular to floor joists are load-bearing. But the only way to be certain is to check the construction and consult a structural engineer.
Structural Engineer Calculations
A chartered structural engineer calculates the load the wall is supporting and specifies the correct RSJ size. They'll produce detailed drawings showing beam size, bearing points (where the beam rests), and any temporary support required during installation.
Why this matters: An undersized beam can fail catastrophically. An oversized beam wastes money and may be too heavy to install safely. The engineer gets it exactly right based on British Standards (BS 5950).
Building Control Notification
We submit the structural engineer's drawings to Building Control (your local council). They review the plans and schedule inspections. This is a legal requirement—work without Building Control approval can make your property unsellable.
Timeline: Building Control typically takes 2-3 weeks to review plans. We don't start work until we have approval. Rushing this step is illegal and dangerous.
Temporary Support Installation
Before we remove any bricks, we install Acrow props (adjustable steel supports) to temporarily hold up the structure above. These props transfer the load to the floor below while we work. We typically use 4-6 props for a standard knock-through.
Safety first: The props stay in place until the RSJ is fully installed and the padstones (concrete blocks that support the beam ends) have cured. Removing props too early can cause collapse.
RSJ Beam Installation
We carefully remove the wall (brick by brick, not with a sledgehammer), install padstones at each end, and lift the RSJ into position. The beam must sit perfectly level and bear evenly on the padstones. We then build up brickwork around the beam ends and allow the mortar to cure.
The details: RSJ beams are heavy (a 3-meter 178mm beam weighs ~70kg). We use lifting equipment and multiple people. The beam is painted with intumescent paint (fire protection) before installation.
Making Good & Building Control Sign-Off
Once the beam is installed and the mortar has cured (typically 7 days), we remove the temporary props. We then "make good"—plastering over the beam, repairing floors/ceilings, and decorating. Building Control inspects the work and issues a completion certificate.
The certificate: This proves the work was done legally and to British Standards. You'll need it when you sell your property. Without it, buyers' solicitors will raise concerns and you may need expensive retrospective approval.
Typical Timeline
A standard knock-through takes 4-6 weeks from initial survey to completion. This includes 2-3 weeks for Building Control approval, 1 week for installation, and 1-2 weeks for making good.
The actual installation (removing wall, installing beam) takes 2-3 days. The rest is planning, approval, and finishing.
Investment Range
Knock-throughs typically cost £3,000-£6,000 including structural engineer (£400-£800), Building Control (£300-£500), RSJ and installation (£1,500-£3,000), and making good (£800-£1,700).
Larger openings, complex structures, or difficult access increase costs. We provide detailed, itemized quotes with no hidden fees.
Find Structural Specialists Near You
We handle structural alterations across South London and Surrey. Select your area: