Structural Steel Beams in London Homes: Installation, Sizing, Costs, and Temporary Works

Key Takeaways

• ✓Structural steel beam sizing for residential work in London must be determined by a qualified structural engineer. The structural engineer calculates the required beam size (expressed as the UB (Universal Beam) section designation — for example, 152x89x16 UB or 203x133x25 UB, where the numbers are depth x width x mass per metre run) based on: the span of the opening (the distance between supports); the load the beam must carry (derived from the floor and roof loads above, and whether the wall carries point loads from structural members above); the type of support conditions at each end of the beam (a beam bearing onto a padstone on a solid brick wall is a different structural condition from a beam bearing onto a column or another beam); and the required deflection limits (a steel beam with excessive deflection under load can crack plasterwork above and feel bouncy). Attempting to size a structural steel beam without a structural engineer's calculation is a building control violation, a structural safety risk, and will not be signed off by Building Control. The structural engineer's structural design fee for a simple residential beam calculation is typically £400–£900; for a more complex multi-beam scheme (rear extension plus loft, multiple structural alterations) the fee may be £900–£2,500
• ✓The most common steel beam sections used in London residential construction are: Universal Beam (UB) sections — the standard I-section beam used for most horizontal spanning applications (lintels, ridge beams, floor beams, transfer beams over wide openings). Common residential sizes run from 152x89x16 UB (for short spans of 1.5–2.5m under modest loading) up to 305x165x40 UB or larger for longer spans or heavy loads. Universal Column (UC) sections — the heavier I-section used where both axial load and bending are significant (columns and posts within a structural frame, or where the structural engineer requires a stiffer section). For a standard residential kitchen opening of 3–4m span in a standard Victorian terrace, the structural engineer typically specifies a 178x102x19 UB to 203x133x25 UB, depending on the load carried. For a wider spanning opening (4–6m, for example, a full rear elevation opening in a kitchen extension), the beam might be a 254x146x31 UB or larger, and may require twin parallel beams (two beams bolted together) where the ceiling depth is insufficient for a single deeper section
• ✓The temporary works sequence for removing a load-bearing wall and installing a structural steel beam is safety-critical and must be carried out in the correct order. The standard sequence for a London residential structural alteration is: (1) Structural engineer approves the design and issues the structural specification (beam size, padstone specification, temporary works methodology where required). (2) The wall below the proposed opening is propped — using acrow props (adjustable steel screw props) or, where the loading requires a spreader arrangement, using a temporary propping system designed by the structural engineer or a temporary works engineer. The props are positioned on either side of the proposed opening, bearing onto spreader boards on the floor below, to transfer the load of the wall above around the opening. (3) The padstones are installed at each end of the proposed beam location — padstones are blocks of dense concrete or engineering brick (typically 215x215x100mm or larger, sized by the structural engineer) that distribute the concentrated point load from the beam end into the supporting wall or column below. (4) The lintel course of brickwork above the proposed opening is cut out, the beam is lifted into position (by hand for smaller sections, by chain block or mini-crane for larger sections), and the beam is bedded onto the padstones. (5) The brickwork or concrete block is rebuilt above the beam, and any required packing between the beam's top flange and the structure above is installed (typically using a dry-pack mortar mix). (6) Once the mortar has cured (typically 24–48 hours), the temporary props are removed. (7) The building inspector assesses the work at the structural stage before making-good (plastering, decoration). A deviation from this sequence — particularly propping inadequately or removing props before the mortar has cured — is a structural safety risk
• ✓The cost of structural steel beam installation in London residential construction varies significantly with the size and number of beams, the access conditions, the extent of making-good required, and the London borough location. Typical cost ranges as of 2025–2026: a single standard kitchen opening (3–3.5m span, one UB beam, two padstones, temporary propping, building control notification, making good included) — £2,500–£5,500 supply and install including making good; a wider rear extension opening (4–6m span, larger or twin beam, more substantial temporary works) — £4,500–£9,000; a full internal remodelling with multiple beams and columns (open-plan ground floor in a Victorian terrace, two or three structural openings, structural engineer design) — £8,000–£18,000 including structural engineer fees, making good, and building control; a steel ridge beam for a loft conversion (spanning the ridge of a double-pitched roof) — £1,500–£4,000 for the ridge beam element alone (usually priced as part of the overall loft conversion package). These costs are for contractor supply-and-install including making good (replastering, skimming, redecorating); they do not typically include the structural engineer's design fee (£400–£900 for a simple residential scheme) or the Building Control application fee (£150–£300 for a structural alteration)
• ✓Structural steel beams in buildings require fire protection to maintain structural integrity in the event of a fire. For a residential building (Building Regulations Part B — Fire Safety), the required fire resistance period is typically 30 minutes for a two-storey house (30 minutes Resistance to Fire or RF), or 60 minutes for a three-storey house or houses converted to flats. Exposed steel fails at approximately 550°C — well below temperatures reached in a building fire. For most residential internal beam installations, the steel beam is inherently fire-protected by the surrounding construction (the plasterboard ceiling below, the brickwork or concrete block above, the plastered soffit). Where the beam is partially or fully exposed below the ceiling line (an exposed steel beam within a modern open-plan ground floor, for example), the structural engineer's specification and the building control application must address fire protection, and the exposed steel must be fire-protected using either: intumescent paint (a specialist expanding paint that swells when heated to form an insulating char layer around the steel — applied in multiple coats to achieve the required fire protection period, typically 60 or 90 minutes); or board encasement (plasterboard or specialist fire-resisting board applied to the flanges and web of the beam to achieve the required fire resistance). Exposed steel beams in residential interiors that are visible after completion (an architectural feature rather than concealed behind ceilings) must have visible fire protection applied — a requirement that should be incorporated into the design from the outset