Steel Beam (RSJ) Installation: Propping, Bearing and Building Control

Quick Answer: A structural steel beam installation involves: temporary propping of the loads above before the wall is opened up; creating a pocket or bearing at each end; positioning the beam with crane, trolley, or manual lifting (for short sections); setting on padstones; and making good. Building Control must inspect and approve both before and during structural works. Never cut an opening in a load-bearing wall without approved calculations, a method statement, and adequate temporary propping in place.

Summary

Installing a steel beam to create an open-plan space, widen a doorway, or carry a loft conversion floor is one of the most common structural tasks in domestic building work. It is also one of the most dangerous phases of a project if the propping is inadequate or the sequence is wrong.

The wall being cut carries loads — floor, roof, or both. These loads are supported by the propping while the opening is formed; they are transferred to the beam once it is seated and grouted. The sequence matters: remove support before the beam is in place and the loads above can deflect, crack, or collapse. Install propping in the wrong position (on a flimsy floor without spreader boards, or in the wrong room) and the propping itself fails.

For experienced builders and structural tradespeople, beam installation is routine. For less experienced workers, the risks of skipping steps — cutting a bigger opening than the calculations allow, using fewer props than specified, not grouting the padstone properly — can be severe. This guide covers the sequence that professional structural contractors follow on domestic beam installations.

Key Facts

• Approved calculations — must be in hand and approved by Building Control before any structural work starts; the beam section, padstone size, bearing length, and propping requirement will all be specified
• Temporary propping — temporary acrow props (scaffold props) carry the loads above while the opening is formed; never cut a load-bearing wall without adequate propping
• Propping locations — props must transfer loads to adequate foundations; use spreader boards (minimum 100×50mm) on timber floors; check the engineer's propping scheme
• Padstones — concrete (typically 100N/mm² dense concrete block, minimum 200mm long, 100mm deep) or engineering brick padstones distribute the beam end load into the masonry; size from the structural calculations
• Bearing length — the length of beam resting on the padstone; minimum specified in calculations, typically 100–150mm for domestic beams
• Steel section grade — typically S275 or S355; confirm from the structural drawings before ordering
• Steel corrosion protection — in wet environments (external wall openings, unheated garages), structural steel should be primed with zinc primer; in dry heated internal locations, paint or intumescent coating may be sufficient per the fire strategy
• Fire protection — structural steel in residential buildings typically needs fire protection to achieve 30 or 60 minutes fire resistance (Part B); intumescent paint (applied at specified DFT) or encasement in plasterboard are the common methods
• Temporary Works Designer — on larger projects, a Temporary Works Designer (or the structural engineer) should specify the propping scheme; for domestic beam installations, the engineer's method statement may include propping guidance
• Maximum manual lift — steel beams over 20–25 kg/m are very heavy; a 3m 254×146×31 UB weighs 93 kg; 4 persons minimum for this size; mobile crane for anything longer or heavier

Quick Reference Table — Common UB Sections for Domestic Use

Actual spans depend on loading — always use the structural engineer's specified section.

Detailed Guidance

Phase 1 — Preparation Before Opening Up

Read the structural drawings completely. Before touching the wall, understand:

• The beam section and grade
• The padstone size and material at each end
• The bearing length required
• The propping scheme (number of props, positions, spreader board requirement)
• Any specific sequence notes from the engineer

Confirm Building Control notification. On a building notice application, you can start work and notify Building Control immediately. On a full plans application, approval must be received before starting structural works. Confirm which route the client has taken before starting.

Order steel early. Common sections are often in stock at local steel stockists (BSS, Metals4U, etc.) but unusual sections may have 1–2 week lead times. Order as soon as the engineer's drawings are received. Confirm section, grade, length (add bearing lengths to the clear span), and surface treatment requirements.

Prepare the propping scheme. Set up acrow props in the rooms above and below as specified by the engineer:

• Props should be plumb and fully extended to bear firmly against the floor/ceiling
• Use 150mm×50mm spreader boards under the base plates on timber floors (4-fold boards spanning perpendicular to floor joists are ideal)
• Position props within 150mm each side of the intended wall face
• On two-storey work, props must run from the top floor down through the ground floor to a solid founding point (concrete floor or solid ground below)

Allow props to settle under load for 30 minutes before starting; check they are all firm.

Phase 2 — Forming the Opening

Mark the opening position. Mark the full opening including the pocket positions for the padstones. The padstone pockets extend 150–200mm into the wall above the lintel level on each side.

Remove the first skin. Use a cold chisel and club hammer (or small SDS drill with chisel bit) to remove the first skin of masonry from the wall between the propping line. Work methodically from the edge of the opening inward. Do not cut the full opening in one pass.

Check for hidden services. Before cutting deeper, scan with a cable avoidance tool (CAT) and check for any gas, water, or electrical services in the wall. On older properties, services in walls are common and may not be where expected.

Form the padstone pockets. Cut the pockets for the padstones at each end of the opening. The pocket must be large enough for the padstone plus 10mm clearance on each side, and deep enough for the padstone thickness plus 30mm bearing in the masonry.

Install padstones. Set the padstones in cement mortar (1:3 mix), level, and allow to set minimum 24 hours before loading the beam. The padstone top face must be level across both ends — use a spirit level and straight edge; check the level measurement across the full span.

Phase 3 — Installing the Beam

Handling and lifting. For beams up to approximately 20 kg/m and lengths up to 4m, manual lifting with 4 persons is achievable with proper lifting technique (split grip, not hoisting from one end). For longer or heavier beams:

• Use a beam trolley or gantry
• Hire a telescopic handler or small crane
• Never attempt to lift a beam that exceeds the manual handling capacity of the team available

Wear steel-toecap boots; a dropped beam foot will cause serious injury.

Positioning. Lift the beam into the opening and onto the padstones. The beam must sit centrally on each padstone with the full bearing length in contact. Check the level along the beam length. On longer spans (over 5m), camber (slight upward bow) is normal and desirable in a steel beam — do not try to force it flat.

Packing the bearing. Once the beam is in position and level, tightly pack the gap between the beam flange and the padstone top face with engineering shims or slate, to take out any variation. Then grout with a non-shrink grout (Sika Grout or equivalent) from one side, allowing it to fill the bearing completely.

Check the beam centreline and height. Confirm the top of the beam is at the correct height for the floor or ceiling structure above. If the beam is in a pocket flush with the ceiling, confirm flush before grouting. If the beam is exposed (feature beam), confirm the height and alignment.

Phase 4 — Making Good and Removal of Props

Grouting cure. Allow non-shrink grout to reach minimum 70% strength before loading the beam (typically 24–48 hours, check product data sheet).

Progressive prop removal. Remove temporary props in the reverse order they were installed — remove the topmost props first, then the lower ones. Never remove all propping simultaneously. As each prop is removed, the load is gradually transferred to the beam and padstones. Check for cracking or deflection as each prop is removed.

Making good around the beam. Collar the beam with herringbone wire mesh or expanded metal lathing, plaster up to the beam flanges, and finish to a smooth plastered surface. Corners at beam bearing points are prone to cracking — use glass-scrim tape (alkali-resistant) at all plasterboard joints around the beam.

Fire protection application. If intumescent paint is required (check Building Control fire strategy), apply at the specified dry film thickness (DFT) per the product data sheet; for 30 minutes fire resistance, typically 400–600 microns DFT in two or three coats. Note that some intumescent products cannot be applied to cold steel — minimum temperature 5°C.

Building Control Inspections

Typical inspection stages for a beam installation:

1. Pre-commencement — Building Control officer may visit before work starts to discuss the scheme; not always required but recommended for first-time builders
2. Steel in position — Building Control will want to see the beam seated on padstones before it is concealed; call to arrange the inspection before making good
3. Completed works — final inspection as part of the overall project completion

Keep a copy of the approved structural drawings on site throughout the works.

Frequently Asked Questions

How do I know if a wall is load-bearing?

Load-bearing walls carry loads from the structure above — floors, roof, or other walls. General indicators (not definitive): walls running perpendicular to floor joists are usually load-bearing; walls in the centre of the house are usually load-bearing; external walls are generally load-bearing. However, construction varies enormously; the only reliable answer comes from the structural engineer assessing the specific property. Never assume — always confirm with an engineer.

Can I install a steel beam in a day?

Propping, opening up, setting padstones, installing beam, and making good — realistically a two-day minimum for a standard domestic installation, allowing one day for the padstone mortar to set. Rushed beam installations that haven't allowed padstone mortar to cure properly are a common source of problems. Plan for two days minimum; book Building Control inspection for day two.

Do I need to treat the steel for corrosion?

For internal beams in heated, dry dwellings — the steel will not corrode significantly in service. Standard mill finish or primer is acceptable. For beams in conservatories, garages, or any location subject to condensation or dampness, apply two coats of zinc-rich primer (Zynolyte or equivalent). For external canopy structures, full galvanising or weathering steel (Corten) may be appropriate.

Regulations & Standards

• BS EN 1993-1-1 (Eurocode 3) — design of steel structures: general rules and rules for buildings

• Approved Document A (2013 edition) — structural stability requirements; padstone and bearing requirements for masonry

• Approved Document B — fire safety: fire resistance requirements for structural elements

• BS 5950 — structural use of steelwork in building (predecessor to Eurocode 3; still referenced in some guidance)

• BS EN 10025 — hot-rolled products of structural steels: S275 and S355 grade specifications

• Steel Construction Institute (SCI) — technical guidance on steel beam design and fire protection

• BCSA Blue Book — section capacity tables for UB and UC sections

• HSE INDG291 — Safe Use of Acrow Props — temporary propping guidance

• structural calculations and engineer's drawings — prerequisite for beam installation

• Party Wall Act requirements — when the beam bears on a party wall

• Building Regulations and Control inspections — notification and inspection requirements

• manual handling for heavy materials — safe lifting of steel sections