Knocking Through: The Science of Removing Walls

Is it Load-Bearing?

This is the first question every client asks. In Victorian terraces, the answer is usually "yes."

Most internal walls in period properties are structural. They support the floor joists of the room above and, often, the timber partitions of the floor above that, right up to the roof. Even a thin lathe-and-plaster wall might be preventing the joists from sagging.

The Steel Beam (RSJ)

When we remove a wall, we must replace it with something stronger. A Rolled Steel Joist (RSJ) is the industry standard. It is dense, stiff, and fire-resistant.

The size of the beam (e.g., 203x102x23) depends on the span and the load. A Structural Engineer calculates this. It is physically impossible to guess. They calculate the "Deflection Limit"—ensuring the beam won't bend more than a few millimeters under load, which would crack your plaster.

The Process: Temporary Propping

You cannot just knock the wall down and put the beam in. Gravity works faster than builders. We must first transfer the weight of the house onto temporary supports.

• Acrow Props: Adjustable steel poles that look like car jacks.
• Strongboys: Steel attachments that slot into the mortar joint above the cut line. They allow us to support the masonry from one side only, which gives us room to work on the other side.
• Needle Beams: For very heavy loads, we knock holes through the wall and insert short timber or steel beams ("needles") supported by props on both sides. This is the safest method.

Only once the props are tight and the structure is motionless do we pick up the demolition hammer.

Padstones: The Unsung Heroes

Steel is strong. Bricks are soft. If you rest a heavy steel beam directly onto a Victorian brick, the concentrated point load will crush the brick into dust.

To prevent this, we install Padstones. These are dense blocks of engineered concrete (concrete strength C30 or C40). They act as a shoe for the beam, spreading the intense weight over a larger area of brickwork.

A common cowboy builder mistake is to use a standard slate or a piece of engineering brick instead of a proper padstone. This will fail Building Control immediately.

Packing: The "Click" Moment

Once the beam is sitting on its padstones, there is usually a tiny gap (10-20mm) between the top of the steel and the joists/brickwork it is meant to support.

We fill this gap with "Dry Pack"—a stiff mixture of sand and cement rammed in hard with a piece of timber. This ensures the load is fully transferred. We leave it to cure (harden) for at least 24 hours. Only then do we slowly release the Acrow props. If we've done it right, the house doesn't move a millimeter. If we hear a creak, we tighten the props and pack again.

Fire Protection: The 30-minute Rule

Steel loses its strength when it gets hot. In a house fire, an unprotected steel beam will buckle in about 15 minutes, bringing the house down.

Building Regulations (Part B) require structural steel to have 30 minutes of fire resistance (or 60 minutes in flats/lofts). We achieve this by:

1. Boarding: Encasing the beam in two layers of 12.5mm Fireline plasterboard (pink board). This is the most common residential method.
2. Intumescent Paint: A special thick paint that swells up into a foam when heated, insulating the steel. This is used if you want the "industrial look" of exposed steel.

Building Control Inspections

You cannot hide a steel beam. A Building Control Inspector must see it before it is covered up. They will check:

• The size of the beam matches the engineer's calculations.
• The padstones are the correct size and material.
• The beam is bolted together correctly (if it's a spliced beam).
• The fire protection is adequate.

Without their "Final Certificate," you will struggle to sell your house in the future. It proves the work is safe.

Party Wall Implications

If the wall you are removing is attached to the party wall (the wall you share with a neighbour), or if the beam needs to be inserted into the party wall, you must serve a Party Wall Notice.

Cutting into the party wall to seat a beam causes vibration and noise. Your neighbour has a legal right to be informed and to have a surveyor check the condition of their wall before you start.