Bifold Doors for London Victorian Homes: Origin, Aluk, Smart, Schüco, Specification, and Build Guide

THE FIRST DECISION IN A LARGE GLAZED OPENING IS WHETHER A BIFOLD DOOR OR A LIFT-AND-SLIDE DOOR SYSTEM IS CORRECT FOR THE PROJECT.

BIFOLD DOORS: EACH DOOR PANEL FOLDS IN ON ITSELF AND STACKS TO ONE OR BOTH SIDES OF THE OPENING WHEN OPEN. A 4-PANEL BIFOLD STACKING TO ONE SIDE LEAVES APPROXIMATELY 50 TO 60% OF THE OPENING FULLY CLEAR WHEN OPEN. PANELS OPEN OUTWARD (OPENING OVER THE PATIO AREA) OR INWARD (OPENING INTO THE ROOM — REDUCING THE AREA OF CLEAR OPENING BY THE PANEL DEPTH OF APPROXIMATELY 400-500MM). INWARD-OPENING IS LESS COMMON IN LONDON (REQUIRES MORE INTERNAL FLOOR SPACE FOR THE STACKED PANELS) BUT IS PERMITTED FOR CONSERVATION AREA APPLICATIONS WHERE PANELS MUST NOT PROJECT OVER THE PATIO.

LIFT-AND-SLIDE DOORS: THE DOOR PANELS SLIDE HORIZONTALLY, WITH A LIFTING MECHANISM THAT RAISES THE PANEL SLIGHTLY OFF THE SILL SEAL FOR SMOOTH MOVEMENT BEFORE LOWERING BACK DOWN WHEN CLOSED FOR MAXIMUM WEATHERTIGHTNESS. A LIFT-AND-SLIDE SYSTEM PROVIDES NARROWER FRAME SIGHTLINES PER PANEL (TYPICALLY 35MM TO 60MM SIGHT LINE VS 107MM FOR ORIGIN BIFOLD) AND CAN ACCOMMODATE MUCH LARGER INDIVIDUAL PANEL SIZES (UP TO 3.0M HIGH X 3.0M WIDE IN SOME SYSTEMS — FAR LARGER THAN THE PRACTICAL MAXIMUM FOR BIFOLD PANELS OF APPROXIMATELY 1.0M X 2.4M PER PANEL). THE SCHÜCO ASS 70.HI LIFT-AND-SLIDE SYSTEM AND THE SMART SYSTEMS VISOGLIDE PLUS ARE THE MOST WIDELY SPECIFIED LIFT-AND-SLIDE SYSTEMS FOR LONDON RESIDENTIAL.

PRACTICAL GUIDANCE FOR LONDON REAR EXTENSIONS: FOR OPENINGS OF 2.4M TO 4.2M IN WIDTH, BIFOLD DOORS ARE THE DOMINANT CHOICE. FOR OPENINGS OF 4.2M OR LARGER, OR WHERE MAXIMUM GLASS AREA PER PANEL IS DESIRED, LIFT-AND-SLIDE OR SLIDING POCKET DOORS (WHERE THE PANELS SLIDE INTO A WALL POCKET — ARCHITECTURALLY VERY CLEAN BUT MORE COMPLEX STRUCTURALLY) ARE INCREASINGLY SPECIFIED.

THE FOLLOWING BIFOLD DOOR SYSTEMS ARE THE MOST WIDELY SPECIFIED IN LONDON RESIDENTIAL EXTENSION PROJECTS, LISTED BY MARKET POSITIONING.

ORIGIN OB-49 (PREMIUM UK MANUFACTURER, THERMALLY BROKEN ALUMINIUM): ORIGIN IS A UK MANUFACTURER BASED IN HIGH WYCOMBE, SELLING DIRECT TO CONSUMERS AND TO BUILDERS THROUGH THEIR NETWORK OF DEALER FABRICATORS. THE OB-49 HAS A 107MM OUTER FRAME DEPTH AND A SIGHTLINE OF APPROXIMATELY 107MM PER FOLD (WHERE TWO PANELS STACK — APPROXIMATELY 214MM TOTAL OF FRAME VISIBLE WHEN OPEN). THE OB-49 IS THERMALLY BROKEN (POLYAMIDE THERMAL BREAK SEPARATING THE OUTER AND INNER ALUMINIUM SECTIONS) AND IS AVAILABLE IN A RANGE OF RAL COLOURS (RAL 7016 ANTHRACITE GREY BEING THE MOST POPULAR FOR LONDON RENOVATIONS IN 2024-2025) WITH UP TO 10 YEARS PAINT WARRANTY ON STANDARD COLOURS. GLAZING: TYPICALLY PILKINGTON OPTIVIEW RANGE ARGON-FILLED DOUBLE GLAZING (6MM TOUGHENED LOW-E / 16MM ARGON / 4MM TOUGHENED) ACHIEVING A WHOLE-UNIT U-VALUE OF APPROXIMATELY 1.3 TO 1.6 W/M'K.

ALUK 58BF (58MM SYSTEM, WIDELY USED BY LONDON FABRICATORS): THE ALUK 58BF IS A 58MM OUTER FRAME SYSTEM OFFERING NARROWER SIGHTLINES THAN THE ORIGIN OB-49 BUT BROADLY SIMILAR THERMAL PERFORMANCE. THE 58BF IS ONE OF THE MOST WIDELY FABRICATED BIFOLD SYSTEMS BY INDEPENDENT LONDON ALUMINIUM FABRICATORS, MAKING IT ACCESSIBLE THROUGH A WIDE NETWORK OF LOCAL SUPPLIERS. STANDARD GLAZING: 44MM DOUBLE-GLAZED UNIT (DGU).

SMART SYSTEMS ALUMINIUM BIFOLD ALITHERM 47 (ENTRY-LEVEL/VALUE): THE ALITHERM 47 IS THE LOWER-COST SMART SYSTEMS BIFOLD OPTION, COMMONLY USED ON BUDGET-CONSCIOUS LONDON EXTENSION PROJECTS. LOWER THERMAL PERFORMANCE THAN ORIGIN OB-49 OR ALUK 58BF.

VUFOLD LUMINA 92MM (WIDE-SIGHTLINE PREMIUM, UK MANUFACTURED): VUFOLD'S LUMINA OFFERS 92MM SIGHTLINES — A MIDPOINT BETWEEN THE ULTRA-SLIM ALUK AND THE WIDER ORIGIN. THE LUMINA IS POPULAR FOR ITS CLEAN PROPORTIONS AND IS AVAILABLE IN DOUBLE OR TRIPLE GLAZING.

TRIPLE GLAZING FOR BIFOLDS: FOR PROJECTS TARGETING VERY HIGH THERMAL PERFORMANCE (APPROACHING PASSIVHAUS), TRIPLE-GLAZED BIFOLD DOORS (4MM TOUGHENED / 14MM ARGON / 4MM FLOAT / 14MM ARGON / 6MM TOUGHENED, TOTAL 42MM UNIT) CAN ACHIEVE CENTRE-PANE U-VALUES OF APPROXIMATELY 0.5 TO 0.7 W/M'K. HOWEVER, TRIPLE-GLAZED BIFOLD DOOR PANELS WEIGH SIGNIFICANTLY MORE THAN DOUBLE-GLAZED — THE HINGE AND TRACK SYSTEM MUST BE RATED FOR THE INCREASED PANEL WEIGHT.

THE STRUCTURAL BEAM (TYPICALLY A UNIVERSAL BEAM — UB — IN STRUCTURAL STEEL S275) CARRYING THE LOAD ABOVE A BIFOLD DOOR OPENING IS ONE OF THE MOST CRITICAL ELEMENTS OF A REAR EXTENSION. THE BEAM MUST BE ENGINEERED FOR THE SPECIFIC SPAN AND LOADING AT THAT LOCATION — DO NOT ASSUME THAT THE SAME BEAM SIZE USED BY A NEIGHBOUR IS CORRECT FOR YOUR OPENING.

TYPICAL UB SIZES FOR BIFOLD DOOR OPENINGS IN LONDON TERRACES: FOR A 2.4M OPENING (TWO-PANEL BIFOLD, CARRYING ROOF/FLOOR ABOVE): UB 152X89X16 OR UB 203X133X25 DEPENDING ON LOAD. FOR A 3.0M OPENING (THREE-PANEL BIFOLD): UB 203X133X25 OR UB 254X146X31 S275. FOR A 4.0M OPENING (FOUR-PANEL BIFOLD): UB 254X146X31 OR UB 305X127X37 S275 DEPENDING ON LOAD. FOR A 5.0M OR LARGER OPENING (FIVE OR SIX-PANEL BIFOLD): UB 305X127X37, UB 356X127X39, OR LARGER — ALWAYS ENGINEER-SPECIFIED.

PADSTONES: THE BEAM END-BEARING PADS ON THE MASONRY PIERS AT EACH SIDE OF THE OPENING MUST BE CORRECTLY DESIGNED. 215X215X100MM PRECAST CONCRETE PADSTONES IN C30/37 CONCRETE OR ENGINEERING BRICK PADSTONES IN CLASS II MORTAR ARE THE STANDARD DETAILS FOR LONDON TERRACE BIFOLD OPENINGS.

BEAM FIRE PROTECTION: WHERE THE STEEL BEAM IS EXPOSED (NOT ENCLOSED IN PLASTERBOARD), NULLIFIRE SC902 INTUMESCENT PAINT MUST BE APPLIED AT SUFFICIENT DRY FILM THICKNESS FOR 30-MINUTE FIRE RESISTANCE. MANY LONDON EXTENSION DESIGNS HAVE THE STEEL BEAM EXPOSED AS AN ARCHITECTURAL FEATURE — MATTE BLACK POWDER COAT OVER INTUMESCENT PRIMER GIVES A CLEAN INDUSTRIAL-CONTEMPORARY LOOK THAT COMPLEMENTS ANTHRACITE GREY BIFOLD FRAMES.

PROPPING DURING INSTALLATION: THE OPENING CANNOT BE FORMED WITHOUT ADEQUATE TEMPORARY PROPPING OF THE STRUCTURE ABOVE. ACROW PROPS ON SOLE PLATES (50X75MM TIMBER SOLE PLATE, MINIMUM 600MM LONG) AT MAXIMUM 1200MM CENTRES EITHER SIDE OF THE OPENING, EXTENDING A MINIMUM OF TWO JOIST BAYS FROM THE OPENING, IS THE STANDARD APPROACH. DO NOT FORM OPENINGS WITHOUT STRUCTURAL ENGINEER-APPROVED PROPPING — UNPROPPED MASONRY COLLAPSE IS A REAL RISK.

BIFOLD DOORS ARE THE LARGEST SINGLE THERMAL WEAKNESS IN ANY EXTENSION ENVELOPE AND MUST MEET BUILDING REGULATIONS PART L REQUIREMENTS.

PART L COMPLIANCE FOR REPLACEMENT AND NEW GLAZING: FOR A REPLACEMENT UNIT (REPLACING EXISTING GLAZING), APPROVED DOCUMENT L REQUIRES A MAXIMUM WHOLE-UNIT U-VALUE OF 1.6 W/M'K FOR DOORS. FOR NEW EXTENSIONS, THE EXTENSION IS ASSESSED AS A WHOLE (TOTAL HEAT LOSS) AGAINST NOTIONAL BUILDING TARGETS — BUT IN PRACTICE, SPECIFYING GLAZED AREAS WITH A U-VALUE OF NO WORSE THAN 1.6 W/M'K IS THE STANDARD TARGET.

PILKINGTON OPTIVIEW (LOW-IRON GLASS): FOR BIFOLD DOORS WHERE MAXIMUM COLOUR NEUTRALITY IS REQUIRED (CLEAR, COLOURLESS GLASS APPEARANCE), PILKINGTON OPTIFLOAT OR OPTIVIEW LOW-IRON GLASS IS SPECIFIED. STANDARD FLOAT GLASS HAS A GREEN TINT VISIBLE ON EDGE — LOW-IRON GLASS IS VIRTUALLY COLOURLESS. IN A LARGE BIFOLD WITH MULTIPLE PANELS, THE TINT DIFFERENCE BETWEEN LOW-IRON AND STANDARD FLOAT IS VISUALLY SIGNIFICANT, PARTICULARLY WITH MULTIPLE PANES.

SOLAR CONTROL GLAZING: FOR SOUTH-FACING EXTENSIONS WITH LARGE BIFOLD OPENINGS, SOLAR OVERHEATING IS A SIGNIFICANT RISK IN SUMMER. SOLAR CONTROL GLAZING (PILKINGTON SOLAR-E, GUARDIAN CLIMAGUARD SOLAR, SAINT-GOBAIN IPASOL) WITH A g-VALUE (SOLAR HEAT GAIN COEFFICIENT) OF 0.30 TO 0.40 (COMPARED TO 0.62 FOR STANDARD LOW-E GLASS) REDUCES SOLAR HEAT GAIN WHILE MAINTAINING GOOD VISIBLE LIGHT TRANSMISSION. BUILDING REGULATIONS PART L COMPLIANCE CALCULATIONS (SAP OR SBEM) MAY REQUIRE SOLAR CONTROL GLAZING FOR LARGE SOUTH-FACING GLAZED AREAS.

BIFOLD DOORS IN LONDON ARE ALMOST ALWAYS PART OF A REAR EXTENSION — THE PLANNING STATUS OF THE EXTENSION DETERMINES THE PLANNING REQUIREMENTS FOR THE BIFOLD DOORS WITHIN IT.

PERMITTED DEVELOPMENT EXTENSIONS: WHERE THE REAR EXTENSION IS PERMITTED DEVELOPMENT (PD) UNDER THE TOWN AND COUNTRY PLANNING ACT AND GPDO 2015 SCHEDULE 2 CLASS A, THE BIFOLD DOORS WITHIN THE EXTENSION DO NOT REQUIRE SEPARATE PLANNING CONSENT. PD REAR EXTENSIONS ARE SUBJECT TO MATERIALS CONDITIONS — THE EXTENSION MUST BE "SIMILAR IN APPEARANCE" TO THE EXISTING HOUSE. FOR MOST LONDON BOROUGHS, ALUMINIUM BIFOLD DOORS IN AN ANTHRACITE GREY RAL 7016 FINISH ARE ACCEPTED AS PD IN A MATERIALS NOTIFICATION CONDITION — BUT CONFIRM WITH THE SPECIFIC LPA.

CONSERVATION AREA PROPERTIES: IN LONDON CONSERVATION AREAS, THE SAME PD RIGHTS FOR REAR EXTENSIONS APPLY (THE REAR OF MOST PROPERTIES IS NOT VISIBLE FROM THE HIGHWAY AND THEREFORE THE CONSERVATION AREA RESTRICTIONS ON EXTERNAL APPEARANCE DO NOT APPLY TO REAR WORKS). HOWEVER, IF A PRIOR APPROVAL APPLICATION IS SUBMITTED UNDER CLASS A (REQUIRED FOR EXTENSIONS OVER 4M DEPTH FOR HOUSES OR 3M FOR FLATS), THE NEIGHBOUR CONSULTATION SCHEME (NCS) PROCESS CONSIDERS IMPACT ON AMENITY — DESIGN QUALITY OF THE DOOR IS NOT SPECIFICALLY ASSESSED.

LISTED BUILDINGS: INSTALLING BIFOLD DOORS IN A LISTED BUILDING REQUIRES BOTH PLANNING PERMISSION (FOR THE EXTENSION) AND LISTED BUILDING CONSENT (FOR THE SPECIFIC DOOR INSTALLATION AND ANY STRUCTURAL WORKS TO THE LISTED FABRIC). LISTED BUILDING OFFICERS IN LONDON BOROUGHS MAY REQUIRE TIMBER BIFOLD DOORS (RATHER THAN ALUMINIUM) TO BE SPECIFIED FOR LISTED PROPERTIES AS THE HERITAGE OFFICER DEEMS MORE APPROPRIATE.

BIFOLD DOOR COSTS IN LONDON VARY SIGNIFICANTLY BASED ON THE SYSTEM SPECIFIED, NUMBER OF PANELS, GLAZING TYPE, AND INSTALLATION COMPLEXITY.

SUPPLY-ONLY COSTS (EXCLUDING INSTALLATION): 3-PANEL BIFOLD (APPROXIMATELY 2.4M WIDTH X 2.1M HEIGHT): ALUK 58BF / SMART ALITHERM 47 (ENTRY): £1,800 TO £3,200. ORIGIN OB-49 (PREMIUM): £3,500 TO £5,500. VUFOLD LUMINA 92MM: £3,000 TO £4,500.

4-PANEL BIFOLD (APPROXIMATELY 3.2M WIDTH X 2.1M HEIGHT): ALUK 58BF: £2,500 TO £4,500. ORIGIN OB-49: £5,000 TO £8,000. SCHÜCO ASS 70.HI LIFT-AND-SLIDE (4-PANEL): £7,000 TO £12,000.

5 OR 6 PANEL BIFOLD (4.0M TO 5.5M WIDTH): ORIGIN OB-49 SUPPLY ONLY: £8,000 TO £15,000.

INSTALLATION BY APPROVED INSTALLER (INCLUDES STEEL LINTEL IF ALREADY PROCURED BY CONTRACTOR, DOOR INSTALLATION, THRESHOLD, SEALANT): £800 TO £2,500 DEPENDING ON COMPLEXITY.

STRUCTURAL STEEL LINTEL (SUPPLY AND INSTALLATION BY BUILDING CONTRACTOR, FOR 3-4M OPENING): £1,200 TO £3,500 INCLUDING STRUCTURAL ENGINEER FEE AND BUILDING CONTROL.

TOTAL BUDGET FOR BIFOLD DOOR OPENING INCLUDING STEEL, BUILDING WORKS, ORIGIN OB-49 DOOR, AND INSTALLATION: £8,000 TO £18,000 DEPENDING ON SPAN AND SPECIFICATION.