Load-bearing wall opening: propping, lintel, method

Extend a kitchen, let in more light, knock two rooms into one: there are a thousand reasons to open up a wall. But as soon as that wall is load-bearing, you are no longer talking about DIY — you are talking about structure. One wrong move and the floor above sags at best; the gable wall cracks at worst. This guide gives you the complete method: identifying a load-bearing wall, getting the right approvals, sizing the lintel, propping correctly and making the opening without putting the house — or anyone in it — at risk.

Load-bearing wall or partition: the distinction that changes everything

A load-bearing wall carries the structural loads: it supports a floor, a roof structure, or a wall from the storey above. Cutting it without precautions removes an essential bearing point. A partition wall carries only itself — you can knock it down with a club hammer without any structural consequences.

How to identify a load-bearing wall

No single criterion is enough on its own. Cross-reference several indicators:

Using original building plans

On architect’s drawings, load-bearing walls are shown with a thicker line and are generally labelled. If you bought a house without plans, ask your local council or planning authority for the original planning permission — the drawings are archived there. Otherwise, a diagnosis by a structural engineer remains the safe route.

Mandatory steps before demolition

Creating an opening in a load-bearing wall is never just an interior job. Two steps are non-negotiable.

1. Structural assessment by a professional

Any modification to a load-bearing wall must be validated by a structural engineer. They calculate:

• The load transfer: how much weight do the floors, walls and roof above the opening exert
• The lintel sizing: what RSJ section or reinforced concrete size is required
• The bearings: how long the lintel must bear on each side, what padstone to specify
• The seismic constraints if you are in a high-risk zone

Budget €400–€1,200 (or equivalent) for an assessment on a standard opening. This is the document your insurer will ask for in the event of a claim — and it is what will prevent your structural warranty being refused.

2. Planning approval

An opening in a load-bearing wall modifies the structure — and often the facade if it faces the outside. Depending on the situation:

Sizing the lintel: the available options

The lintel is the beam that carries the loads above the opening. The choice depends on the span (opening width), the loads, the wall thickness and the context.

The 4 common solutions

The most common choice in renovation is the RSJ (Rolled Steel Joist), as it offers the best span-to-depth ratio. For a 2 m opening in a 200 mm concrete block wall carrying a timber floor, a 160 RSJ (or equivalent HEA 140) is typical — but only the structural engineer can confirm.

Universal installation rules

Whatever lintel you choose:

• Minimum bearing: 200 mm on each side of the opening (often 250–300 mm recommended by structural engineers)
• Padstone under each bearing: solid concrete block or cast concrete pad, to prevent the wall punching through
• Bedded in expanding grout or hydraulic mortar: never dry-laid
• Ring beam continuity: if the opening cuts through a horizontal ring beam, the lintel must replace it (bonded reinforcement ties required)

Propping: the critical step

Before touching a single brick, you must transfer the loads away from the wall. This is where safety is won or lost — the majority of site collapses stem from inadequate propping.

Principle

Two lines of props are installed parallel to the wall, one on each side, at approximately 500 mm from the face of the future opening. They carry a needle beam (or a light steel section) in contact with the ceiling, which thereby takes the loads from the upper floor throughout the duration of the works.

ABSOLUTE rules

1. Prop onto a hard surface: never onto a timber floor without a spreader. Place a 40 × 150 mm minimum spreader board at the foot of each prop to distribute the load to the ground.
2. Certified steel props only: ban improvised timber props. Use adjustable steel props such as Acrow or RMD, certified to BS EN 1065, with an admissible load of 15 to 30 kN each.
3. Maximum spacing of 1 m between props on the line.
4. Upper needle beam in full contact with the ceiling (or the beam above): pack with a compressed timber wedge if needed.
5. Progressive tightening: tighten slightly, check, re-tighten. You are not lifting the house — you are simply picking up the load.
6. Prop on both faces if the wall is load-bearing in a multi-storey house: loads come from both sides via the joists.

Duration of propping

The props remain in place:

• Throughout the entire cutting of the wall
• During the installation of the lintel and its grouting
• For at least 7 days after grouting with traditional mortar, 28 days if the lintel is an in-situ cast concrete beam

Do not touch the props before this period is up, even if the lintel appears to be holding.

Step-by-step method

Here is the complete sequence for a 2 m wide opening in a 200 mm load-bearing concrete block wall.

Step 1 — Mark out

1. Snap a chalk line on the floor and ceiling to mark the axis of the opening
2. Transfer the vertical sides using a plumb line
3. Mark the lintel line: standard door height (2100 mm) + lintel depth (200–250 mm depending on RSJ chosen)
4. Mark the lintel bearing pockets: 250 mm each side, height = RSJ depth + 30 mm clearance

Step 2 — Protect and prop

1. Isolate electricity to the zone and verify with a multimeter
2. Protect the floor with dust sheets and boards
3. Clear furniture within a 3 m radius
4. Install the propping as described above, on both faces of the wall, at approximately 500 mm
5. Check the plumb of each prop with a spirit level (absolutely vertical)

Step 3 — Create the bearing pockets

1. Cut the outlines of the pockets with an angle grinder (230 mm diamond blade)
2. Break out the blocks with a pneumatic chisel hammer or SDS breaker
3. Vacuum the dust and dampen the pocket faces
4. Pour a concrete padstone (C25/30) at the bottom of each pocket: 100 mm deep over the full wall thickness
5. Allow to cure for a minimum of 48 hours before setting the RSJ

Step 4 — Set the lintel

1. Offer up the RSJ dry: check it fits into the pockets with 10–20 mm clearance each side
2. Spread a bed of expanding grout (Sikagrout or equivalent) on the padstones
3. Set the RSJ: adjust with a spirit level (or laser level) — the soffit of the lintel must be perfectly horizontal
4. Pack above the RSJ with expanding grout or lean concrete: there must be no gap, no void between the RSJ and the masonry above (otherwise the RSJ deflects before picking up the load)
5. Allow to cure for at least 7 days

Step 5 — Cut the opening below the lintel

1. Check one last time that the props are perfectly tight and the lintel has cured
2. Cut the outlines of the opening with the angle grinder (at least 2 new blades)
3. Demolish from the top down, course by course: the load transfers progressively onto the lintel
4. Remove the debris as you go
5. Finish at floor level respecting the threshold dimension (if door) or sill height (if window)

Step 6 — Finish the reveals and threshold

1. Square off the reveals with mortar (straight, plumb jambs)
2. Fit liners and jambs if installing a window or door frame
3. Pour a concrete threshold if external opening
4. Wait a minimum of 21 days before removing the props — ideally 28 days if the lintel is in-situ concrete

Decision tree: who does what?

Indicative budget

For a 2 m opening in a 200 mm load-bearing concrete block wall:

Classic mistakes that cost dearly

1. Skipping the structural engineer’s report: if a claim occurs, no insurer will cover you
2. Inadequate propping: timber props, spacing > 1 m, no spreader at the base — the number one cause of accidents
3. Lintel bearing too short: 100 mm instead of 250 mm — punching of the block, progressive settlement
4. Gap between lintel and masonry above: the RSJ deflects before picking up the load, stair-step cracks in the gable
5. Demolishing from the bottom rather than the top: the load drops suddenly, risk of collapse
6. Removing props too early: cracking guaranteed in the weeks that follow
7. Ignoring hidden services: electrical conduits, concealed pipework — always start with a borescope inspection (plumber’s camera, €30 hire)
8. Forgetting fire protection on an exposed RSJ: in dwellings, intumescent paint or a plasterboard boxing is required by Building Regulations

Useful links

• To understand how loads travel through a house, read our guides on choosing foundation type and horizontal and vertical ring beams
• Before starting, master the basics: building concrete block walls and forming a window or door lintel
• For planning matters: householder application vs full planning permission
• Key organisations and references: RICS (Royal Institution of Chartered Surveyors), IStructE (Institution of Structural Engineers), HSE (Health and Safety Executive — propping safety), LABC (Local Authority Building Control)

Final checklist