Aluminium Windows for London Victorian Homes: Performance, Systems, and Conservation Area Rules

ALUMINIUM IS AN EXCELLENT CONDUCTOR OF HEAT — AN ADVANTAGE IN SUMMER (QUICK TO HEAT UP) BUT A MAJOR PROBLEM IN WINTER (COLD BRIDGES THROUGH THE FRAME THAT CAUSE CONDENSATION AND HEAT LOSS). STANDARD (NON-THERMALLY-BROKEN) ALUMINIUM WINDOWS HAVE VERY POOR THERMAL PERFORMANCE AND ARE NOT SUITABLE FOR MODERN UK BUILDINGS.

THERMALLY BROKEN (TB) ALUMINIUM: A POLYAMIDE (NYLON) THERMAL BREAK STRIP IS PRESSED OR POURED INTO THE ALUMINIUM EXTRUSION — SEPARATING THE INNER AND OUTER ALUMINIUM SECTIONS AND DRAMATICALLY REDUCING HEAT CONDUCTION. THERMALLY BROKEN ALUMINIUM WINDOW SYSTEMS ACHIEVE PART L (2021) COMPLIANCE FOR REPLACEMENT WINDOWS — MINIMUM U-VALUE 1.4 W/M²K (WHOLE-WINDOW, FOR REPLACEMENT WINDOWS IN EXISTING BUILDINGS).

CURRENT LEADING TB ALUMINIUM SYSTEMS FOR UK RESIDENTIAL (2025-2026):

SMART ALUMINIUM VISOFOLD (ALUMINIUM BIFOLD/SLIDING): SMART ARCHITECTURAL ALUMINIUM — ONE OF THE LARGEST UK MANUFACTURERS. VISOFOLD 1000 (BIFOLD) AND VISOGLIDE PLUS (LIFT-AND-SLIDE). STANDARD 32MM POLYAMIDE THERMAL BREAK; AVAILABLE IN ANY RAL COLOUR AND DUAL COLOUR; BRITISH-MADE. COMMON ACROSS LONDON EXTENSIONS AND REFURBISHMENTS.

VELFAC 200 COMPOSITE SYSTEM: ALUMINIUM OUTER / TIMBER INNER — A COMPOSITE SYSTEM RATHER THAN PURE ALUMINIUM. TRIPLE GLAZED OPTION AVAILABLE (0.8 W/M²K WHOLE-WINDOW). EXCELLENT THERMAL PERFORMANCE; NATURAL TIMBER INTERIOR SURFACE; POPULAR IN HIGH-SPECIFICATION REFURBISHMENTS. ALUMINIUM OUTER AVAILABLE IN ANY RAL COLOUR.

ALUK 58BF BIFOLD: ALUK (FRENCH MANUFACTURER, STRONG UK DISTRIBUTION) — 58MM FRAME DEPTH, 14MM SIGHTLINES, THERMALLY BROKEN. COMPETITIVE THERMAL PERFORMANCE; POPULAR FOR LONDON EXTENSION BIFOLD APPLICATIONS. ALSO: ALUK SL38 SLIDING SYSTEM (38MM SIGHTLINES, LIFT-AND-SLIDE MECHANISM) FOR HIGH-SPECIFICATION APPLICATIONS.

ORIGIN OB-49 BIFOLD: ORIGIN — UK MANUFACTURER — 75MM OUTER FRAME, 107MM STACKING WHEN OPEN. ORIGIN IS THE PREMIUM UK BIFOLD BRAND — PREMIUM PRICING BUT STRONG SERVICE NETWORK AND CONSISTENT QUALITY. POPULAR FOR MID-TO-HIGH SPECIFICATION LONDON PROJECTS.

RATIONEL ALDAS (TRIPLE GLAZED): RATIONEL (DANISH MANUFACTURER, UK DISTRIBUTION) — TIMBER-ALUMINIUM COMPOSITE; TRIPLE GLAZED STANDARD; WHOLE-WINDOW U-VALUE 0.8-1.0 W/M²K. PASSIVHAUS-COMPATIBLE. EXCELLENT FOR ENERGY-FOCUSED REFURBISHMENTS. NATURAL PINE INTERIOR.

STANDARD CASEMENT AND SASH WINDOWS — TB ALUMINIUM: FOR STANDARD CASEMENT WINDOWS: SMART ARCHITECTURAL ALUMINIUM STEEL FS / SMART SIEGER; ALUK 58BD; SCHUCO AWS 75.SI. FOR FLUSH SASH (REPLICAS OF TRADITIONAL TIMBER SASH): SMART FLUSH CASEMENT FS; THERMALLY IMPROVED PRODUCTS THAT GIVE THE APPEARANCE OF TRADITIONAL TIMBER WITHOUT THE MAINTENANCE.

WINDOW REPLACEMENT IN CONSERVATION AREAS IS A CONTENTIOUS PLANNING TOPIC IN LONDON. THE FOLLOWING APPLIES:

PERMITTED DEVELOPMENT (NO PLANNING PERMISSION REQUIRED): REPLACEMENT WINDOWS THAT ARE LIKE-FOR-LIKE (SAME SIZE, SAME CONFIGURATION, SAME MATERIAL APPEARANCE) ARE GENERALLY PERMITTED DEVELOPMENT EVEN IN CONSERVATION AREAS — BECAUSE THE CHANGE IS MINOR AND DOES NOT ALTER THE CHARACTER. HOWEVER, IN MOST LONDON CONSERVATION AREAS, REPLACING TIMBER SASH WINDOWS WITH ALUMINIUM WINDOWS — EVEN IF SIMILARLY-SIZED — IS NOT CONSIDERED LIKE-FOR-LIKE AND REQUIRES PLANNING PERMISSION.

CONSERVATION AREA CONSENT (NOW PLANNING PERMISSION): A PLANNING APPLICATION IS REQUIRED FOR: CHANGING WINDOW MATERIAL (TIMBER TO ALUMINIUM); CHANGING WINDOW TYPE (SASH TO CASEMENT OR VICE VERSA); SIGNIFICANT CHANGES TO SIZE OR CONFIGURATION; AND INSTALLATION OF NEW WINDOWS IN EXISTING OPENINGS THAT HAD NO WINDOW.

WHAT PLANNERS ACCEPT IN LONDON CONSERVATION AREAS: - SLIM-SECTION ALUMINIUM SYSTEMS THAT CLOSELY REPLICATE TRADITIONAL TIMBER SASH PROPORTIONS MAY BE ACCEPTABLE TO SOME LONDON BOROUGH CONSERVATION OFFICERS - IN PRACTICE, MANY CONSERVATION OFFICERS IN LONDON STRONGLY PREFER TIMBER SASH WINDOW RESTORATION OR REPLACEMENT (IN TIMBER) OVER ANY ALUMINIUM SYSTEM — PARTICULARLY ON FRONT ELEVATIONS - REAR AND INTERNAL COURTYARD ELEVATIONS ARE TYPICALLY TREATED MORE FLEXIBLY - FLUSH CASEMENT ALUMINIUM SYSTEMS (E.G. SMART FLUSH FS) ARE SOMETIMES ACCEPTED WHERE EXISTING WINDOWS WERE CASEMENT - PRE-APPLICATION ADVICE FROM THE CONSERVATION OFFICER IS ESSENTIAL BEFORE SPECIFYING ALUMINIUM IN A CONSERVATION AREA

LISTED BUILDINGS: LISTED BUILDING CONSENT IS REQUIRED FOR ANY WINDOW CHANGES — AND IS ALMOST NEVER GRANTED FOR ALUMINIUM WINDOWS ON GRADE II LISTED BUILDINGS IN LONDON. TIMBER REPAIR OR REPLACEMENT IN MATCHING TIMBER IS THE STANDARD APPROVED APPROACH.

UNDERSTANDING THE WHOLE-WINDOW U-VALUE VERSUS THE CENTRE-PANE GLASS U-VALUE IS CRITICAL — MARKETING MATERIALS OFTEN LEAD WITH THE GLASS U-VALUE WHICH IS ALWAYS BETTER THAN THE WHOLE-WINDOW PERFORMANCE.

PART L (2021) U-VALUE REQUIREMENTS FOR WINDOWS: FOR REPLACEMENT WINDOWS IN EXISTING BUILDINGS (CONSERVATION APPROACH): WHOLE-WINDOW U-VALUE MAXIMUM 1.4 W/M²K. FOR NEW-BUILD WINDOWS (INCLUDING NEW EXTENSION WINDOWS): WHOLE-WINDOW U-VALUE AS LOW AS POSSIBLE AS PART OF THE SAP TARGET EMISSION RATE CALCULATION — TYPICALLY SPECIFYING 1.0-1.2 W/M²K OR BETTER IS GOOD PRACTICE.

GLAZING SPECIFICATION FOR ALUMINIUM FRAMES: STANDARD DOUBLE GLAZING (ARGON-FILLED, LOW-E COAT): CENTRE-PANE UG=1.0-1.1 W/M²K; WHOLE-WINDOW WITH ALUMINIUM FRAME ~1.4-1.6 W/M²K. ENHANCED DOUBLE GLAZING (WARM EDGE SPACER, IMPROVED LOW-E COAT, E.G. PILKINGTON ENERGIKILOGA): CENTRE-PANE UG=0.9-1.0 W/M²K; WHOLE-WINDOW ~1.2-1.4 W/M²K. TRIPLE GLAZING (E.G. SAINT-GOBAIN CLIMAPLUS ULTRA N): CENTRE-PANE UG=0.5-0.7 W/M²K; WHOLE-WINDOW WITH HIGH-PERFORMANCE FRAME ~0.8-1.0 W/M²K.

SOLAR CONTROL GLAZING (SOUTH-FACING EXTENSIONS): FOR SOUTH-FACING EXTENSIONS WITH LARGE GLAZED AREAS, SOLAR GAIN CAN CAUSE OVERHEATING. OPTIONS: - PILKINGTON ACTIV SOLAR NEUTRAL: SOLAR FACTOR (G) 0.40; LIGHT TRANSMISSION 70% — REDUCES SOLAR GAIN BY 60% - SAINT-GOBAIN SUNBAN 62/35: G=0.35; LT=62% — HIGH SOLAR CONTROL - GUARDIAN SUNGUARD SOLAR: DUAL-FUNCTION LOW-E + SOLAR CONTROL SOLAR CONTROL GLASS REDUCES COOLING LOADS IN SUMMER BUT SLIGHTLY REDUCES WINTER SOLAR GAIN — THE BALANCE SHOULD BE ASSESSED BY THE ARCHITECT.

ALUMINIUM WINDOW INSTALLATION COSTS VARY SIGNIFICANTLY WITH: SYSTEM SPECIFICATION; NUMBER AND SIZE OF OPENINGS; STRUCTURAL WORKS REQUIRED (LINTELS, STRUCTURAL OPENINGS); AND WHETHER SCAFFOLDING IS NEEDED.

TYPICAL LONDON MARKET COSTS (SUPPLY AND INSTALL, 2025-2026): STANDARD CASEMENT WINDOW (1.2M X 1.2M, TB ALUMINIUM, DOUBLE GLAZED, SMART OR ALUK SYSTEM): - SUPPLY: £600-1,200 PER WINDOW - INSTALLATION (INCLUDING REMOVAL OF EXISTING): £300-500 PER WINDOW - TOTAL PER WINDOW: £900-1,700

FLUSH SASH CASEMENT (REPLICA SASH APPEARANCE): - SUPPLY: £800-1,600 PER WINDOW - INSTALLATION: £350-600 PER WINDOW - TOTAL PER WINDOW: £1,150-2,200

BIFOLD DOOR (4.5M WIDE X 2.1M HIGH, ORIGIN OB-49 OR ALUK 58BF): - SUPPLY: £4,000-8,000 (4-5 PANEL) - INSTALLATION (INCLUDING STRUCTURAL LINTEL): £1,000-2,000 ADDITIONAL - TOTAL: £5,000-10,000

SLIDING DOOR (4.0M WIDE X 2.1M HIGH, LIFT-AND-SLIDE ALUK SL38 OR SCHUCO): - SUPPLY: £5,000-10,000 - INSTALLATION: £1,000-2,000 ADDITIONAL

TRIPLE GLAZED CASEMENT (RATIONEL ALDAS OR VELFAC 200): - SUPPLY: £1,200-2,500 PER WINDOW - INSTALLATION: £400-700 PER WINDOW

FENSA SELF-CERTIFICATION: REPLACEMENT WINDOW INSTALLATIONS MUST BE CERTIFIED BY A FENSA-REGISTERED OR CERTASS-REGISTERED INSTALLER — THEY SELF-CERTIFY COMPLIANCE WITH BUILDING REGULATIONS PART L AND ISSUE A CERTIFICATE. IF USING A NON-REGISTERED INSTALLER, A BUILDING REGULATIONS APPLICATION MUST BE MADE TO THE LOCAL AUTHORITY. FENSA/CERTASS CERTIFICATES ARE IMPORTANT FOR PROPERTY SALE (SOLICITORS REQUEST THEM ON TA6 PROPERTY INFORMATION FORMS).