Window Draught Proofing for London Victorian Terraces: A Complete Guide

VICTORIAN TIMBER SASH AND CASEMENT WINDOWS WERE NEVER DESIGNED TO BE AIRTIGHT. WHEN NEW, THEY RELIED ON OPEN FIREPLACES TO PROVIDE VENTILATION AND EXTRACT MOISTURE FROM THE BUILDING — THE DRAUGHT WAS, TO A DEGREE, INTENTIONAL. TODAY, WITH CENTRAL HEATING AND SEALED CHIMNEY FLUES, THAT SAME INFILTRATION BECOMES UNCOMFORTABLE AND COSTLY.

THE PRIMARY DRAUGHT SOURCES IN A DOUBLE-HUNG SASH WINDOW ARE: THE MEETING RAIL GAP (WHERE UPPER AND LOWER SASH MEET IN THE MIDDLE — TYPICALLY 2-5MM CLEARANCE WHEN WORN); THE STAFF BEAD SIDES (WHERE THE LOWER SASH RUNS IN THE FRAME — WORN PAINTED BEADS LEAVE 3-6MM GAPS); THE PULLEY HOLES (SMALL GAPS WHERE THE CORDS PASS THROUGH THE PULLEY STILE, OFTEN STUFFED WITH RAG OR LEFT OPEN); AND GENERAL FRAME-TO-REVEAL GAPS WHERE OLD PUTTY AND COMPOUND HAS FAILED.

FOR CASEMENT WINDOWS, THE MAIN DRAUGHT PATHS ARE: FAILED OR MISSING COMPRESSION SEALS AROUND THE SASH PERIMETER; WORN HINGES CAUSING THE SASH TO SIT PROUD OF THE FRAME; CRACKED OR MISSING GLAZING COMPOUND AROUND THE GLASS; AND GAP AT THE MEETING STILE WHERE TWO CASEMENTS MEET.

ENERGY SAVINGS TRUST DATA SUGGESTS A WELL-DRAUGHT-PROOFED HOME CAN SAVE £25-65 PER YEAR ON HEATING BILLS. FOR A VICTORIAN TERRACE WITH 8-12 ORIGINAL SASH WINDOWS, THE CUMULATIVE DRAUGHT IS SIGNIFICANT — AIR PERMEABILITY TESTING (BLOWER DOOR TEST) ON UNIMPROVED VICTORIAN TERRACES TYPICALLY SHOWS 12-20 M³/H/M² AT 50 PA VERSUS THE PART L 2021 TARGET OF 8 M³/H/M² FOR NEW BUILDS.

PILE WEATHERSTRIPPING (ALSO CALLED BRUSH STRIP OR MOHAIR PILE) IS THE MOST EFFECTIVE AND REVERSIBLE DRAUGHT-PROOFING METHOD FOR TIMBER SASH WINDOWS. THE SYSTEM INVOLVES ROUTING A GROOVE INTO THE SASH SIDES AND MEETING RAILS, THEN PRESSING IN A POLYPROPYLENE PILE STRIP THAT COMPRESSES AGAINST THE FRAME AS THE SASH SLIDES.

VENTROLLA IS THE MARKET-LEADING SPECIALIST CONTRACTOR IN THE UK. THEIR STANDARD PILE SPECIFICATION IS: 5MM PILE HEIGHT, 9MM BODY WIDTH, POLYPROPYLENE PILE IN A POLYPROPYLENE CARRIER — DESIGNED TO ALLOW THE SASH TO SLIDE FREELY WHILE SEALING AGAINST DRAUGHTS. VENTROLLA QUOTE AN 85-95% REDUCTION IN AIR INFILTRATION THROUGH THE WINDOW AFTER TREATMENT.

THE VENTROLLA SYSTEM ALSO INCLUDES: RENOVATION OF THE SASH CORDS (REPLACING WITH WOVEN COTTON OR SPIRALIFT SPRING BALANCE); PLANING AND SEALING THE SASH STILES; OVERHAULING THE PULLEYS; SEALING PULLEY HOLES WITH THEIR PATENTED DRAUGHT-PROOF PULLEY; AND FITTING POLISHED CHROME FITCH CATCHES TO THE MEETING RAIL.

TYPICAL VENTROLLA COST: £150-300 PER WINDOW FOR PILE ONLY; £250-600 PER WINDOW FOR FULL RENOVATION INCLUDING CORD REPLACEMENT AND OVERHAULING. A 6-WINDOW VICTORIAN TERRACE FRONT ELEVATION TYPICALLY COSTS £1,200-2,500 FOR FULL RENOVATION AND WEATHERSTRIP. VENTROLLA OFFER A 20-YEAR GUARANTEE ON THEIR PILE SYSTEM.

ALTERNATIVE SPECIALIST CONTRACTORS INCLUDE SASH WINDOW EXPERTS (LONDON-BASED), THE SASH WINDOW WORKSHOP, AND VARIOUS JOINERY FIRMS OFFERING SIMILAR PILE SYSTEMS. ALWAYS CHECK THEY ROUTE A PROPER GROOVE RATHER THAN SURFACE-GLUING FOAM STRIP — SURFACE-APPLIED FOAM DEGRADES WITHIN 2-5 YEARS AND CAUSES THE SASHES TO STICK.

FOR DIY PILE INSTALLATION: PURCHASE PILE STRIP FROM EXITEX OR SCHLEGEL (AVAILABLE FROM BUILDBASE, JEWSON, OR ONLINE). CUT A GROOVE 9-10MM WIDE AND 5-6MM DEEP INTO THE SASH SIDES USING A ROUTER WITH STRAIGHT BIT. PRESS THE PILE IN — IT CLIPS IN WITHOUT ADHESIVE. THE CHALLENGE IS ACHIEVING A STRAIGHT GROOVE ON CURVED OR IRREGULAR PERIOD TIMBER WITHOUT A ROUTER JIG — MOST HOMEOWNERS FIND PROFESSIONAL INSTALLATION WORTHWHILE FOR THIS REASON.

FOR HOMEOWNERS WHO WANT TO TACKLE DRAUGHT PROOFING THEMSELVES, THE FOLLOWING PRODUCTS AND APPROACHES ARE AVAILABLE, LISTED FROM MOST TO LEAST EFFECTIVE:

SELF-ADHESIVE FOAM TAPE (LOWEST COST, LOWEST DURABILITY): DRAUGHT EXCLUDER FOAM TAPE SUCH AS RONSEAL FOAM DRAUGHT EXCLUDER, EVERBUILD WINDOW SEAL, OR STANDARD FOAM TAPE FROM TOOLSTATION. TYPICALLY 5MM X 5MM OR 9MM X 6MM. SUITABLE FOR CASEMENT WINDOWS WHERE THE SASH COMPRESSES AGAINST THE SEAL — NOT SUITABLE FOR SASH WINDOWS WHERE THE SASH SLIDES ACROSS THE SEAL (FOAM TEARS WITHIN WEEKS). COST: £2-8 PER ROLL (5-10 METRES). LIFESPAN: 2-5 YEARS ON CASEMENTS.

SELF-ADHESIVE PILE STRIP: BRANDS INCLUDE EXITEX PILESEALTEX AND SCHLEGEL Q-LON. PEEL-AND-STICK 9MM PILE THAT ADHERES TO THE SASH GROOVE WITHOUT ROUTING. PERFORMANCE IS SIGNIFICANTLY LOWER THAN ROUTED PILE — THE ADHESIVE FAILS WITHIN 3-7 YEARS AND THE PILE IS NOT COMPRESSED INTO A GROOVE SO IT FLATTENS UNDER SLIDING SASH FRICTION. COST: £8-18 PER METRE LENGTH.

FLEXIBLE SILICONE SEAL: ARBOSEAL OR BOSTIK SUPERFIX FLEXIBLE SILICONE CAN BE APPLIED TO FIXED FRAME-TO-REVEAL JOINTS, GLAZING COMPOUND CRACKS, AND FIXED FRAME PERIMETERS. COLOURLESS OR PAINTABLE (EVERBUILD 502 TRADE). DO NOT APPLY TO OPENING JOINTS — IT PREVENTS OPENING AND LOOKS POOR. COST: £4-12 PER CARTRIDGE.

BRUSH STRIP FOR CASEMENTS: EXITEX MACCOURT OR REDDIPLEX BRUSH STRIP WITH SELF-ADHESIVE BACKING. PRESS INTO THE REBATE AROUND THE CASEMENT PERIMETER BEFORE CLOSING. MORE DURABLE THAN FOAM ON CASEMENTS — SUITABLE FOR MODERATE COMPRESSION. COST: £6-15 PER WINDOW.

LETTER BOX DRAUGHT EXCLUDERS AND KEYHOLE COVERS: PERKINS LETTER BOX SEAL OR ARC DRAUGHT PROTECTOR FOR THE LETTER BOX FLAP; KEYHOLE COVER FROM TOOLSTATION. THESE ADDRESS ADDITIONAL INFILTRATION POINTS IN FRONT DOORS OFTEN MISSED. COST: £5-20 EACH.

CHIMNEY BALLOONS AND DRAUGHT STOPPERS: WHERE SEALED CHIMNEY FLUES CREATE A COLD COLUMN OF AIR FALLING INTO THE ROOM IN WINTER, A CHIMNEY BALLOON (CHIMNEY SHEEP, BALLOON DR, THERMAPLUG) BLOCKS THE FLUE. IMPORTANT: ALWAYS ATTACH A REMINDER TAG BEFORE THE FIREPLACE — FORGETTING TO REMOVE BEFORE LIGHTING A FIRE IS A SERIOUS CARBON MONOXIDE RISK. COST: £15-35.

SECONDARY GLAZING IS THE MOST EFFECTIVE THERMAL AND ACOUSTIC UPGRADE FOR ORIGINAL SASH WINDOWS, AND IS TYPICALLY ACCEPTABLE IN CONSERVATION AREAS WITHOUT PLANNING PERMISSION WHEN INSTALLED INTERNALLY. IT IS HIGHLY EFFECTIVE AS A DRAUGHT-PROOFING MEASURE BECAUSE IT CREATES A SECOND AIR BARRIER INSIDE THE EXISTING WINDOW.

THE COMBINED PERFORMANCE OF A RESTORED AND PILE-WEATHERSTRIPPED ORIGINAL SASH WINDOW WITH SECONDARY GLAZING IS APPROXIMATELY: - ORIGINAL UNRESTORED SINGLE-GLAZED SASH: U-VALUE ~5.0-5.5 W/M²K, AIR INFILTRATION HIGH - RESTORED + PILE WEATHERSTRIPPED ONLY: U-VALUE ~4.5-5.0 W/M²K, AIR INFILTRATION REDUCED 85-95% - RESTORED + PILE + SECONDARY GLAZING (STANDARD GLASS): U-VALUE ~1.8-2.2 W/M²K - RESTORED + PILE + SECONDARY GLAZING (PILKINGTON SPACIA VACUUM): U-VALUE ~1.0-1.4 W/M²K

SELECTAGLAZE SYSTEMS: THE UK\'S LEADING SECONDARY GLAZING SPECIALIST. KEY PRODUCTS: - SERIES 10: FIXED PANEL (HINGED FOR CLEANING) — SUITABLE FOR UPPER SASH THAT IS RARELY OPENED. THICKNESS 6-28MM SEALED UNIT OR SINGLE SHEET. - SERIES 35: HORIZONTAL SLIDING — THE MOST COMMON FOR DOUBLE-HUNG SASH WINDOWS. TWO PANES SLIDE HORIZONTALLY FOR VENTILATION. ALLOWS ACCESS TO THE ORIGINAL WINDOW. - SERIES 45: VERTICAL SLIDING — MIRRORS THE MOVEMENT OF THE SASH WINDOW BELOW. PREMIUM OPTION. SELECTAGLAZE COST: SUPPLY AND INSTALLATION TYPICALLY £300-700 PER WINDOW FOR SERIES 35.

PILKINGTON SPACIA 6.4MM VACUUM GLAZING: THIS IS A SINGLE UNIT THAT ACTS LIKE A DOUBLE-GLAZED UNIT BUT AT ONLY 6.4MM THICKNESS. U-VALUE 0.7 W/M²K (CENTRE PANE — BETTER THAN STANDARD DOUBLE GLAZING). SUITABLE FOR SECONDARY GLAZING INNER PANE OR FOR REPLACING THE ORIGINAL SINGLE GLASS IN THE SASH REBATE (CHECK REBATE DEPTH — MINIMUM 9MM REQUIRED). COST: £500-1,000+ PER WINDOW INSTALLED.

MAGNETITE SECONDARY GLAZING: DIY MAGNETIC FRAME SYSTEM (ALSO AVAILABLE VIA SPECIALISTS). USES A MAGNETIC PERIMETER FRAME STUCK TO THE EXISTING WINDOW REVEAL, WITH AN ACRYLIC OR GLASS PANE THAT PRESSES ON MAGNETICALLY. COST: £100-250 PER WINDOW (MAGNETITE BRAND DIY KIT). PERFORMANCE IS SLIGHTLY LOWER THAN SELECTAGLAZE DUE TO LESS RIGID SEAL, BUT VERY EASY TO REMOVE IN SUMMER.

MHB (MAGNETIC HINGED SECONDARY GLAZING): SIMILAR MAGNETIC SYSTEM BUT WITH HINGED OPENING. USED BY ENGLISH HERITAGE AND HISTORIC ENGLAND IN LISTED BUILDINGS. COST: £150-350 PER WINDOW.

CASEMENT WINDOWS (SIDE-HINGED SASHES COMMON IN 1930S AND LATER PROPERTIES IN LONDON, THOUGH ALSO FOUND IN SOME LATE VICTORIAN PROPERTIES) HAVE DIFFERENT DRAUGHT PATHS AND SOLUTIONS TO SASH WINDOWS.

COMPRESSION SEAL REPLACEMENT: THE ORIGINAL DRAUGHT SEAL ON CASEMENT WINDOWS IS A COMPRESSION SEAL (RUBBER OR NEOPRENE) THAT SQUASHES AGAINST THE FRAME STOP WHEN THE WINDOW IS CLOSED. THIS DEGRADES OVER TIME — TYPICALLY 10-20 YEARS. REPLACEMENT PRODUCTS: - REDDIPLEX BUBBLE GASKET RP2-BS — TUBULAR RUBBER PROFILE 9MM DIAMETER — SUITABLE FOR TIMBER CASEMENTS WITH 3-6MM GAP - EXITEX P-PROFILE EPDM SEAL — SELF-ADHESIVE — SUITABLE FOR SMALLER 1-3MM GAPS - SCHLEGEL Q-LON COMPRESSION SEAL — FOAM CORE EPDM SKIN — MEDIUM COMPRESSION 4-8MM GAP COST: £5-15 PER WINDOW (DIY MATERIALS)

HINGE REPAIR AND ALIGNMENT: WORN OR LOOSE HINGES ON CASEMENTS CAUSE THE SASH TO HANG PROUD OF THE FRAME, LEAVING A GAP AT THE LATCH SIDE OR TOP/BOTTOM. REPAIRS INCLUDE: TIGHTENING HINGE SCREWS (FILL OLD HOLES WITH WOODEN MATCHSTICKS AND PVA BEFORE RE-SCREWING IF THREADS ARE STRIPPED); FITTING LARGER HINGES (EGERTON AE55 OR MILA PROLINEA) WHERE THE FRAME IS SOUND; OR ADDING HINGE PACKERS TO ADJUST ALIGNMENT. COST: £20-60 PER WINDOW FOR HINGE REPLACEMENT.

GLAZING BEAD SEAL: ON TIMBER CASEMENTS, APPLY A CONTINUOUS BEAD OF CLEAR SILICONE (EVERBUILD 502 TRADE) TO THE JOINT BETWEEN GLASS AND GLAZING BEAD WHERE PUTTY HAS CRACKED OR SHRUNK AWAY. DO NOT APPLY TO THE SASH-TO-FRAME JOINT — ONLY FIXED JOINTS. THIS PREVENTS INFILTRATION THROUGH THE GLAZING BEAD WHILE MAINTAINING OPENABILITY.

HANDLE AND ESPAGNOLETTE: MULTI-POINT LOCKING HANDLES (MILA PROLINEA ESPAGNOLETTE) COMPRESS THE SASH AGAINST THE SEAL AT MULTIPLE POINTS WHEN LOCKED. ON OLDER CASEMENTS WITH A SINGLE PEG LATCH, THE TOP AND BOTTOM OF THE SASH MAY BOW AWAY FROM THE FRAME. REPLACING WITH A MULTI-POINT SYSTEM SIGNIFICANTLY IMPROVES THE SEAL. COST: £60-150 PER WINDOW FOR HANDLE REPLACEMENT.

DRAUGHT PROOFING COSTS AND TYPICAL ANNUAL SAVINGS FOR A LONDON VICTORIAN TERRACE WITH 6 SASH WINDOWS:

DIY FOAM TAPE (ALL WINDOWS): £30-80 MATERIALS. ANNUAL SAVING: MINIMAL (FOAM DEGRADES QUICKLY ON SASH WINDOWS — NOT RECOMMENDED). ROI: POOR.

DIY PILE STRIP (ALL WINDOWS): £80-200 MATERIALS. ANNUAL SAVING: £15-30. ROI: 3-7 YEARS. NOTE: DIFFICULT TO INSTALL NEATLY WITHOUT ROUTING SKILLS.

PROFESSIONAL PILE WEATHERSTRIP (VENTROLLA OR SIMILAR): £900-2,000 FOR 6-WINDOW PROGRAMME. ANNUAL SAVING: £25-50. ROI: 18-40 YEARS ON ENERGY ALONE — BUT THE REAL VALUE IS COMFORT AND THE 20-YEAR GUARANTEE.

SECONDARY GLAZING (SELECTAGLAZE SERIES 35, 6 WINDOWS): £1,800-4,200 INSTALLED. ANNUAL SAVING ON HEATING: £60-120. ROI: 15-25 YEARS. ADDITIONAL VALUE: SIGNIFICANT ACOUSTIC IMPROVEMENT (PARTICULARLY BENEFICIAL ON BUSY LONDON STREETS — TYPICAL REDUCTION OF 35-45 DB).

COMBINED PILE + SECONDARY GLAZING (6 WINDOWS): £2,700-6,200 INSTALLED. ANNUAL SAVING: £80-170. ROI: 16-39 YEARS. BEST ALL-ROUND OUTCOME FOR CONSERVATION AREA PROPERTIES WHERE REPLACEMENT GLAZING IS NOT PERMITTED.

NOTE: ENERGY SAVINGS ALONE RARELY JUSTIFY THE COST OF PROFESSIONAL DRAUGHT PROOFING AND SECONDARY GLAZING ON A PURE ROI BASIS. THE REAL CASE IS THE COMBINATION OF: COMFORT (COLD RADIATION AND DRAUGHTS ELIMINATED); ACOUSTIC PERFORMANCE (CITY NOISE REDUCED); PROPERTY VALUE (IMPROVED EPC RATING); AND HERITAGE COMPLIANCE (RETAINING ORIGINAL WINDOWS IN CONSERVATION AREAS).