Structural Openings and Steel Beams Guide for London Homes

A STRUCTURAL BEAM OVER A NEW OPENING IN A LONDON HOUSE MUST CARRY: (1) THE SELF-WEIGHT OF THE MASONRY ABOVE THE OPENING (EITHER A TRIANGLE OF BRICK "ARCHING ACTION" IF THE WALL IS SOUND AND THE OPENING GEOMETRY ALLOWS, OR THE FULL WEIGHT OF BRICK/BLOCK/FLOOR/ROOF ABOVE IF ARCHING CANNOT BE RELIED UPON — THE ENGINEER WILL ASSESS WHICH APPLIES); (2) IMPOSED (LIVE) LOADS — PEOPLE, FURNITURE, AND SNOW ON FLOORS AND ROOFS ABOVE THE BEAM. FOR UK RESIDENTIAL: FLOOR IMPOSED LOAD IS 1.5 KN/M2 (BS EN 1991-1-1:2002); ROOF IMPOSED LOAD IS 0.6-1.0 KN/M2 PLUS WIND. (3) DEAD LOADS — THE SELF-WEIGHT OF FLOORS, CEILINGS, FINISHES, AND WALLS ABOVE. THE STRUCTURAL ENGINEER CALCULATES THE TOTAL LOAD ON THE BEAM AND SELECTS A STEEL SECTION (FROM THE BRITISH STEEL SECTIONS TABLE) THAT: (A) HAS SUFFICIENT BENDING STRENGTH (MOMENT CAPACITY — THE BEAM MUST NOT YIELD OR FRACTURE UNDER MAXIMUM LOAD); (B) HAS SUFFICIENT SHEAR CAPACITY AT THE BEARING POINTS (ENDS OF THE BEAM); (C) DEFLECTS BY NO MORE THAN SPAN/360 UNDER FULL LIVE LOAD AND SPAN/250 UNDER TOTAL LOAD (THE DEFLECTION LIMIT TO PREVENT VISIBLE SAGGING AND DAMAGE TO PARTITIONS AND FINISHES BELOW). THE MOST COMMON STEEL SECTIONS IN LONDON RESIDENTIAL WORK: UC (UNIVERSAL COLUMN — DEEP AND WIDE FLANGE, IDEAL WHERE DEFLECTION IS CRITICAL OR WHERE BEAM HEIGHT IS CONSTRAINED): UC 152X152X23, UC 203X203X46, UC 254X254X73. UB (UNIVERSAL BEAM — DEEPER SECTION, EFFICIENT FOR LONGER SPANS): UB 203X133X25, UB 254X146X31, UB 305X127X37, UB 356X171X45.

THE SHORT ANSWER IS: ALWAYS — FOR ANY LOAD-BEARING WALL OPENING IN LONDON. BUILDING REGULATIONS PART A (STRUCTURE) REQUIRES THAT STRUCTURAL ALTERATIONS (INCLUDING FORMING NEW OPENINGS IN LOAD-BEARING WALLS) ARE DESIGNED BY A QUALIFIED STRUCTURAL ENGINEER (CHARTERED MEMBER OF THE INSTITUTION OF STRUCTURAL ENGINEERS — MIStructE — OR CHARTERED MEMBER OF THE ICE — MICE WITH STRUCTURAL SPECIALISM). A STRUCTURAL ENGINEER FOR A TYPICAL LONDON OPENING (SINGLE SPAN, 1-3M, SINGLE-STOREY TERRACE) WILL: (1) CALCULATE THE DESIGN LOADS ON THE BEAM (UDL — UNIFORMLY DISTRIBUTED LOAD — AND ANY POINT LOADS FROM ABOVE); (2) DETERMINE THE MINIMUM STEEL SECTION FROM BS EN 1993-1-1 (EUROCODE 3 — DESIGN OF STEEL STRUCTURES) AND/OR BS 5950 (OLDER REFERENCE STILL USED BY SOME ENGINEERS); (3) SPECIFY THE PADSTONE (LOAD-SPREADING BEARING PLATE) AT EACH END OF THE BEAM — TYPICALLY ENGINEERING BRICK OR CONCRETE PADSTONE (100X215X65MM CONCRETE PADSTONE FOR A STANDARD RESIDENTIAL BEAM — SIZE INCREASES WITH LOAD); (4) ISSUE A STRUCTURAL ENGINEER'S REPORT AND CALCULATIONS FOR SUBMISSION TO BUILDING CONTROL; (5) FOR COMPLEX CASES: SPECIFY TEMPORARY WORKS (PROPS AND NEEDLES) REQUIRED DURING THE INSTALLATION. COSTS FOR A STRUCTURAL ENGINEER IN LONDON: SIMPLE SINGLE OPENING (RESIDENTIAL, 1-3M SPAN): £300-£600 FOR CALCULATIONS AND REPORT. COMPLEX OPENING OR MULTIPLE OPENINGS (HOUSE REMODELLING): £600-£1,500. STAGE INSPECTION (ENGINEER VISITS SITE DURING INSTALLATION TO CONFIRM STEEL IS CORRECTLY POSITIONED): £150-£300.

BEFORE ANY LOAD-BEARING WALL CAN BE OPENED UP, THE LOADS FROM ABOVE MUST BE TEMPORARILY SUPPORTED TO AVOID COLLAPSE DURING THE WORK. THIS IS CALLED TEMPORARY WORKS. THE SEQUENCE FOR A TYPICAL LONDON TERRACE KITCHEN OPENING (REMOVING A 2M SECTION OF GROUND-FLOOR REAR WALL TO MERGE KITCHEN AND DINING ROOM): (1) ERECT TIMBER NEEDLE BEAMS (75X225MM C24 TIMBER OR UC STEEL, RUNNING THROUGH THE WALL AT 90° — PERPENDICULAR TO THE WALL — AT APPROXIMATELY 600MM SPACING ABOVE THE PROPOSED OPENING. THE NEEDLES PASS THROUGH HOLES FORMED IN THE WALL AND ARE SUPPORTED ON ACROW PROPS (SCAFFOLD PROPS — THE MOST COMMON TEMPORARY SUPPORT IN LONDON RESIDENTIAL WORK) ON EACH SIDE OF THE WALL. (2) ACROW PROPS (GROUNDFORCE HP4 OR SIMILAR — RATED TO 2-6 TONNE PER PROP) ARE PLACED ON SPREADER BOARDS (SOLE BOARDS — MINIMUM 600X225X50MM C24 TIMBER) TO DISTRIBUTE THE LOAD ONTO THE FLOOR SLAB OR JOISTS. SPREADER BOARDS PREVENT POINT LOADS GOING THROUGH THE FLOOR DIRECTLY. (3) THE LOAD IS TRANSFERRED FROM THE WALL TO THE NEEDLES TO THE PROPS. NOW THE BRICKWORK BELOW THE NEEDLE LINE CAN BE SAFELY REMOVED. (4) THE STEEL BEAM IS LIFTED (MECHANICAL LIFTING OR MANUAL WITH A BEAM TROLLEY — BEAMS ABOVE 150KG REQUIRE MECHANICAL AIDS) AND SET ON THE PADSTONES. (5) MORTAR IS PACKED TIGHTLY BETWEEN THE TOP FLANGE OF THE BEAM AND THE BRICKWORK ABOVE ("PACKING" — BLUE ENGINEERING BRICK SLIPS OR CEMENT: SAND MORTAR PACK) TO ENSURE FULL BEARING CONTACT. (6) NEEDLES AND PROPS ARE REMOVED ONCE THE BEAM IS FULLY BEDDED AND PACKING HAS SET. THE MOST COMMON TEMPORARY WORKS FAILURE IN LONDON: NOT USING SPREADER BOARDS UNDER ACROW PROPS ON TIMBER JOIST FLOORS — THE POINT LOAD FROM A SINGLE ACROW PROP CAN EXCEED THE SAFE LOAD ON A SINGLE TIMBER JOIST, CAUSING LOCAL DEFLECTION OR FAILURE.

THE FOLLOWING ARE TYPICAL STRUCTURAL BEAM SPECIFICATIONS FOR COMMON LONDON RESIDENTIAL SCENARIOS (THESE ARE INDICATIVE ONLY — A STRUCTURAL ENGINEER MUST CONFIRM ALL SPECIFICATIONS FOR ACTUAL PROJECTS): (1) REMOVING A NON-LOAD-BEARING PARTITION (STUD WALL, NO LOAD ABOVE): NO STEEL BEAM REQUIRED. A TIMBER LINTEL OVER THE DOOR OPENING IF ONE IS CREATED IS SUFFICIENT. ALWAYS CONFIRM WITH A STRUCTURAL ENGINEER BEFORE ASSUMING A WALL IS NON-LOAD BEARING — IN LONDON TERRACE HOUSES, INTERNAL WALLS ARE SOMETIMES LOAD-BEARING IN WAYS THAT ARE NOT OBVIOUS FROM VISUAL INSPECTION. (2) OPENING UP A 2.0M SECTION OF GROUND-FLOOR REAR WALL (1-STOREY ABOVE, LONDON TERRACE): TYPICAL SPECIFICATION: UC 152X152X23 (S275 STEEL), 50MM CONCRETE PADSTONES AT EACH BEARING. (3) OPENING UP A 3.0M SECTION OF GROUND-FLOOR REAR WALL (2-STOREY ABOVE, LONDON TERRACE): TYPICAL SPECIFICATION: UC 203X203X46 (S275 OR S355 STEEL), 75MM CONCRETE PADSTONES. (4) OPENING UP A 4.0M SECTION (WIDE OPENING FOR BIFOLD DOORS, 2-STOREY ABOVE): TYPICAL SPECIFICATION: UB 305X165X40 OR UB 356X171X45 (S355 STEEL), PADSTONES DESIGNED PER ENGINEER CALCULATIONS. (5) CHIMNEY BREAST REMOVAL (FIRST FLOOR, WITH CHIMNEY STACK ABOVE): TYPICALLY TWO SHORT STEEL BEAMS (UB 127X76X13 OR UC 152X152X23 ON EACH FLANK WALL) TO SUPPORT THE REMAINING CHIMNEY BREAST ABOVE — SPECIFIC TO EACH CASE, ALWAYS REQUIRES STRUCTURAL ENGINEER. CATNIC AND IG LINTELS: FOR SMALLER OPENINGS (STANDARD DOOR WIDTH: 900MM, WINDOW 1200MM), PROPRIETARY STEEL LINTELS (CATNIC CG90/100, IG STANDARD LINTEL) ARE USED RATHER THAN STRUCTURAL BEAMS. THESE ARE PRE-DESIGNED AND SIZED TO STANDARD SPAN TABLES (AVAILABLE FROM THE LINTEL MANUFACTURERS).

STRUCTURAL OPENINGS IN LONDON TERRACES FREQUENTLY INVOLVE PARTY WALL OBLIGATIONS UNDER THE PARTY WALL ETC. ACT 1996: SECTION 2 — WORKS TO A PARTY STRUCTURE: A PARTY WALL IS THE SHARED WALL BETWEEN NEIGHBOURING TERRACE HOUSES. THE FOLLOWING STRUCTURAL WORKS TO A PARTY WALL REQUIRE A PARTY WALL NOTICE TO BE SERVED UNDER SECTION 2 OF THE ACT: CUTTING INTO A PARTY WALL (E.G. TO INSTALL A BEAM END THAT BEARS ON THE PARTY WALL — THE BEAM POCKET OR PADSTONE IS SET INTO THE PARTY WALL MASONRY); MAKING GOOD OR CUTTING THE PARTY WALL TO INSTALL FLASHINGS, TIES, OR DAMP-PROOF COURSES. IN PRACTICE, ALMOST ALL LONDON TERRACE STRUCTURAL OPENINGS WHERE THE BEAM BEARS ON THE PARTY WALL REQUIRE SECTION 2 PARTY WALL NOTICE. THE PARTY WALL NOTICE MUST BE SERVED AT LEAST 2 MONTHS BEFORE THE PLANNED START DATE (FOR SECTION 2 NOTICES). THE ADJOINING OWNER CAN: CONSENT (IN WRITING — WORK CAN PROCEED ON THE AGREED DATE); DISSENT (TRIGGERING THE ACT'S DISPUTE RESOLUTION PROCEDURE — AN AGREED SURVEYOR OR TWO SEPARATE SURVEYORS ARE APPOINTED TO DETERMINE THE TERMS OF A PARTY WALL AWARD). SECTIONS 1 AND 6 ARE ALSO RELEVANT IN SOME LONDON OPENING SCENARIOS: SECTION 1 (BUILDING ON LINE OF JUNCTION — APPLICABLE TO NEW WALL BUILT ON OR ASTRIDE THE BOUNDARY); SECTION 6 (EXCAVATIONS WITHIN 3M OF ADJACENT BUILDING FOUNDATIONS).

STRUCTURAL OPENING AND BEAM INSTALLATION COSTS IN LONDON (2025, PER JOB): STRUCTURAL ENGINEER (CALCULATIONS + REPORT): £300-£600 (SINGLE OPENING). BUILDING CONTROL APPLICATION FEE (BUILDING NOTICE — TYPICALLY 2-3% OF NOTIONAL BUILDING WORK COST, MIN £200): £200-£500. PARTY WALL AGREED SURVEYOR FEE (IF REQUIRED): £700-£1,500. TEMPORARY WORKS (ACROW PROPS, NEEDLES, SPREADER BOARDS): £300-£600 (HIRE + INSTALLATION). STEEL BEAM SUPPLY (UC 152X152X23, 3.0M LONG): £150-£250. STEEL BEAM SUPPLY (UC 203X203X46, 3.0M LONG): £300-£450. BEAM DELIVERY AND LIFTING (HIAB CRANE OR CHAIN HOIST): £200-£400. INSTALLATION OF SINGLE BEAM (LABOUR ONLY, INCLUDING PADSTONES, PACKING, MAKING GOOD ABOVE AND BELOW): £800-£1,500. TOTAL FOR A TYPICAL LONDON TERRACE 2-3M OPENING (STRUCTURAL ENGINEER + BEAM + INSTALL + DECORATION): £3,000-£6,000. STEEL BEAM INSTALLATION FOR A 4-5M WIDE BIFOLD DOOR OPENING IN A LONDON KITCHEN EXTENSION (LARGER BEAM, FLITCH PLATED OR COMPOUND STEEL): £5,000-£10,000 TOTAL INCLUDING ALL OF THE ABOVE. FIRE PROTECTION OF STEEL BEAMS: IF THE BEAM IS EXPOSED IN A HABITABLE ROOM (NOT BOXED IN WITH FIRELINE BOARD), INTUMESCENT PAINT (JOTUN JOTACHAR 1709) MUST BE APPLIED BY A SPECIALIST TO ACHIEVE FIRE RESISTANCE (R30 OR R60 AS REQUIRED BY BUILDING REGULATIONS PART B). INTUMESCENT PAINT APPLICATION: £400-£1,000 PER BEAM DEPENDING ON BEAM SIZE AND FIRE RATING REQUIRED.