Draught-Proofing Timber Sash Windows in London Victorian Terraces: Seals, Refurbishment, and Secondary Glazing

THE AIR INFILTRATION THROUGH AN ORIGINAL UNREFURBISHED TIMBER SASH WINDOW IN A LONDON VICTORIAN TERRACE IS SIGNIFICANT — TYPICALLY 2-3X THAT OF A MODERN DOUBLE-GLAZED CASEMENT WINDOW — AND OCCURS THROUGH MULTIPLE PATHWAYS:

PRIMARY AIR INFILTRATION PATHWAYS IN A LONDON VICTORIAN TERRACE SASH WINDOW: 1. MEETING RAIL (WHERE THE TOP SASH AND BOTTOM SASH OVERLAP AT THE MIDPOINT OF THE WINDOW): THE MOST SIGNIFICANT SINGLE AIR-INFILTRATION POINT — THE MEETING RAIL SURFACES ARE TYPICALLY FLAT SOFTWOOD AGAINST FLAT SOFTWOOD WITH A GAP OF 3-10MM AFTER 100+ YEARS OF PAINT BUILDUP, WARPING, AND SHRINKAGE. 2. SASH-TO-FRAME SIDE GAPS (WHERE THE SASH STILE SLIDES IN THE PULLEY STILE CHANNEL): TYPICALLY 3-6MM EACH SIDE — ALLOWS CONTINUOUS AIR FLOW UP THE SASH BOX CHANNEL AND INTO THE ROOM. 3. BOTTOM RAIL TO SILL (WHERE THE BOTTOM SASH SITS ON THE WINDOW BOARD/SILL): TYPICALLY 5-10MM GAP — PARTICULARLY PRONOUNCED AFTER YEARS OF SASH CORD STRETCHING, WHICH LOWERS THE SASH POSITION. 4. TOP RAIL OF TOP SASH TO FRAME HEAD (THE HIGHEST POINT OF THE TOP SASH): SIMILAR TO THE BOTTOM RAIL ISSUE — OFTEN 5-10MM GAP. 5. PULLEY AXLES (THE IRON SASH PULLEYS THEMSELVES ALLOW DIRECT AIR COMMUNICATION WITH THE SASH BOX CAVITY — WHICH IS UNINSULATED AND COMMUNICATES WITH THE CAVITY BETWEEN THE OUTER WALL FACES).

IMPACT OF AIR INFILTRATION IN LONDON VICTORIAN TERRACE SASH WINDOWS: AN UNREFURBISHED ORIGINAL TIMBER SASH WINDOW IN A LONDON VICTORIAN TERRACE MAY ACCOUNT FOR 25-35% OF THE TOTAL FABRIC HEAT LOSS OF THE DWELLING (ENERGY SAVING TRUST ESTIMATE — COMBINING CONDUCTION THROUGH SINGLE GLASS AND INFILTRATION THROUGH AIR GAPS). A COMPLETE DRAUGHT-PROOFING REFURBISHMENT OF ALL SASH WINDOWS IN A TYPICAL 3-BED LONDON VICTORIAN TERRACE (4-6 WINDOWS) CAN REDUCE HEATING BILLS BY AN ESTIMATED £50-100 PER YEAR AND SIGNIFICANTLY IMPROVE COMFORT — ELIMINATING THE COLD DRAUGHTS THAT MAKE SITTING NEAR THE WINDOWS UNCOMFORTABLE IN WINTER.

THE PRINCIPAL DRAUGHT-PROOFING SEALING SYSTEM FOR TIMBER SASH WINDOWS IS THE BRUSH PILE SEAL — A FOLDED POLYPROPYLENE PILE STRIP (LIKE A MINIATURE BRUSH) THAT IS FITTED INTO ROUTED OR KERFED CHANNELS CUT INTO THE TIMBER OF THE SASH OR FRAME, PROVIDING A SLIDING SEAL BETWEEN THE MOVING SASH AND THE FIXED FRAME WITHOUT SIGNIFICANTLY INCREASING FRICTION.

REDDISEALS SASH WINDOW DRAUGHT PROOFING KIT (THE MOST WIDELY SPECIFIED PROFESSIONAL SASH WINDOW DRAUGHT-PROOFING SYSTEM IN THE UK): REDDISEALS LTD (BASED IN ESSEX) SUPPLIES THE PILE SEAL SYSTEMS USED BY THE MAJORITY OF PROFESSIONAL SASH WINDOW REFURBISHMENT CONTRACTORS IN LONDON. REDDISEALS WS1 PILE STRIP (6MM HIGH X 4MM WIDE POLYPROPYLENE PILE — WHITE OR BROWN): FITTED INTO A 5X3.5MM KERF CUT BY A DEDICATED REDDISEALS ROUTING MACHINE INTO THE SASH STILE AND THE FRAME PULLEY STILE — PROVIDES THE SIDE-CHANNEL SEAL (CLOSES THE 3-6MM SIDE GAP THAT ALLOWS SASH BOX AIR INFILTRATION). REDDISEALS WF FOAM COMPRESSOR STRIP (FOR THE MEETING RAIL): A COMBINED FOAM COMPRESSOR + PILE SEAL THAT SEALS THE MEETING RAIL FACES WHEN THE SASHES ARE CLOSED WITHOUT PREVENTING OPERATION. REDDISEALS WS2 PILE STRIP (FOR THE BOTTOM RAIL AND TOP RAIL — NARROW PILE FITTED INTO A KERF IN THE PARTING BEAD GROOVE): SEALS THE GAPS AT THE BOTTOM OF THE BOTTOM SASH AND THE TOP OF THE TOP SASH.

EXITEX PERIMETER SEAL (ALTERNATIVE TO REDDISEALS — AVAILABLE THROUGH BUILDERS MERCHANTS INCLUDING SCREWFIX AND JEWSON): EXITEX WINDOW DRAUGHT SEAL (SELF-ADHESIVE FOAM STRIP — EPDM SPONGE — 9X4MM): SUITABLE FOR SURFACES THAT DO NOT SLIDE (E.G. THE MEETING RAIL FACE — APPLIED TO ONE RAIL FACE SO IT COMPRESSES WHEN THE SASH CLOSES). NOT SUITABLE FOR SIDE CHANNELS WHERE THE SASH SLIDES (WOULD CAUSE EXCESSIVE FRICTION AND PREVENT SMOOTH OPERATION). EXITEX LOWLINE DOOR AND WINDOW STRIP (FOR BOTTOM RAIL TO SILL — WIPER BRUSH TYPE — FITTED TO INSIDE FACE OF BOTTOM SASH RAIL): PROVIDES A FLEXIBLE WIPER ACTION AT THE BOTTOM RAIL/SILL JUNCTION.

COMPLETE SASH WINDOW REFURBISHMENT (REMOVING THE SASHES, REPAIRING THE FRAME, REPLACING CORDS AND PULLEYS, AND RE-FITTING WITH DRAUGHT-PROOFING SEALS) PROVIDES THE MOST COMPREHENSIVE AND DURABLE IMPROVEMENT TO A LONDON VICTORIAN TERRACE SASH WINDOW.

SASH CORD REPLACEMENT: ORIGINAL SASH CORDS ARE TWISTED HEMP OR WAXED COTTON — LIFESPAN 30-60 YEARS. WHEN THE CORD BREAKS, THE COUNTERBALANCE SASH WEIGHT FALLS INTO THE SASH BOX AND THE SASH BECOMES DIFFICULT TO OPERATE. REPLACEMENT CORD: BS EN 1979 WAXED POLYPROPYLENE SASH CORD (STRAND HARDWARE OR WINDOW CARE SYSTEMS — 9MM DIAMETER, SOLD BY THE METRE) OR PRE-STRETCHED COTTON SASH CORD (FOR HERITAGE RESTORATION WHERE COTTON IS SPECIFIED BY CONSERVATION OFFICER). SASH WEIGHTS (CAST IRON): THE ORIGINAL CAST-IRON COUNTERBALANCE WEIGHTS FOUND IN LONDON VICTORIAN TERRACE SASH BOXES ARE TYPICALLY 3-6KG PER WEIGHT (MATCHING THE SASH WEIGHT) — THESE SHOULD BE REUSED IF IN GOOD CONDITION; REPLACEMENT CAST-IRON WEIGHTS ARE AVAILABLE FROM ARCHITECTURAL SALVAGE YARDS (LASSCO, LONDON OR SALVO NETWORK) OR SPECIALIST SUPPLIERS (STRAND HARDWARE).

SASH PULLEY REPLACEMENT: ORIGINAL SASH PULLEYS ARE TYPICALLY CAST-IRON FACE-FIX WITH AN AXLE AND WHEEL — PRONE TO CORROSION AND SQUEAKING. REPLACEMENT: WINDOW CARE SYSTEMS BRASS SASH PULLEY (FACE-FIX, 44MM PLATE — STANDARD SIZE FOR LONDON VICTORIAN TERRACE FRAMES). PARTING BEAD REPLACEMENT: THE PARTING BEAD (THE THIN STRIP OF TIMBER THAT RUNS VERTICALLY IN THE SASH CHANNEL, SEPARATING THE TOP AND BOTTOM SASH CHANNELS) IS TYPICALLY ORIGINAL PINE — OFTEN WARPED OR PAINT-CLOGGED. REPLACEMENT: 10X3MM SOFTWOOD PARTING BEAD (REDDISEALS OR BESPOKE FROM TIMBER MERCHANT — PRIMED AND PAINTED). DRAUGHT-PROOFING SEAL FITTING ON PARTING BEAD: THE REDDISEALS ROUTING SYSTEM CUTS KERFS INTO THE NEW PARTING BEAD AND SASH STILES TO ACCEPT THE PILE STRIPS.

SPIRAL BALANCE REPLACEMENT (ALTERNATIVE TO SASH CORD AND WEIGHTS — FOR DAMAGED SASH BOXES): WHERE THE SASH BOX IS TOO DAMAGED OR INACCESSIBLE TO REPAIR (E.G. A STAFF BEAD HAS BEEN FIXED PERMANENTLY, OR THE BOX LINING HAS BEEN SKIM-PLASTERED OVER), SPIRAL (CLOCK SPRING) BALANCES (WINDOW CARE SYSTEMS WCS SPIRAL BALANCE OR CALDWELL BALANCE) CAN REPLACE THE CORD-AND-WEIGHT SYSTEM: THE SPIRAL BALANCE CONCEALS INSIDE THE PULLEY STILE CHANNEL — FITTED THROUGH THE POCKET HOLES — AND A STAINLESS SPRING PROVIDES THE COUNTERBALANCE.

BEYOND THE SASH-TO-FRAME SEALS, TWO ADDITIONAL AIR INFILTRATION PATHWAYS IN LONDON VICTORIAN TERRACE SASH WINDOWS ARE OFTEN OVERLOOKED: THE PULLEY AXLE OPENINGS (WHICH COMMUNICATE DIRECTLY WITH THE SASH BOX CAVITY — AN UNINSULATED VOID BETWEEN THE BOX LINING AND THE EXTERNAL BRICKWORK) AND THE SASH BOX LOWER POCKET COVERS (WHICH ARE LOOSE-FIT SOFTWOOD ACCESS PANELS IN THE LOWER BOX LINING).

PULLEY SEAL: WINDOW CARE SYSTEMS PULLEY SEALS (PLASTIC COVER PLATES THAT FIT OVER THE EXISTING SASH PULLEY AXLE AND FACE PLATE — AVAILABLE IN WHITE, CREAM, AND BROWN TO MATCH PAINTED OR STRIPPED FRAMES): THE PLASTIC COVER PLATE HAS A FLEECE SURROUND THAT SEATS AGAINST THE FRAME FACE AND REDUCES AIR FLOW THROUGH THE PULLEY AXLE SPACE. COST: APPROXIMATELY £2 TO £5 PER PULLEY SEAL (4 PULLEYS PER SASH WINDOW — 2 PER SASH).

SASH BOX LOWER POCKET COVER SEALING: THE POCKET COVER (LOOSE-FIT SOFTWOOD PANEL — 150X100MM APPROXIMATELY — IN THE BOTTOM OF THE FRAME BELOW THE LOWER SASH) CAN BE DRAUGHT-SEALED WITH: SELF-ADHESIVE FOAM STRIP (EXITEX 9X4MM EPDM) APPLIED TO THE POCKET COVER PERIMETER — COMPRESSES WHEN THE POCKET COVER IS FITTED, ELIMINATING GAPS.

SASH WINDOW SECURITY UPGRADING: AN ORIGINAL LONDON VICTORIAN TERRACE SASH WINDOW HAS ONLY A FITCH FASTENER (THE BUTTERFLY CAM-AND-KEEPER THAT PULLS THE MEETING RAILS TOGETHER — PROVIDES NO REAL SECURITY). SECURITY UPGRADES: FITCH FASTENER + SASH STOP (WOODEN PEG OR BRASS SASH STOP — PREVENTS THE LOWER SASH FROM BEING SLID OPEN FROM OUTSIDE). DUAL SCREW LOCKING SYSTEM (WINDOW CARE SYSTEMS DUAL SCREW — A BOLTED LOCK THAT PASSES THROUGH BOTH MEETING RAILS — SOLD SECURE RATED). SASH RESTRICTOR (ALLOWS VENTILATION POSITION — LOWER SASH OPEN 100-150MM FOR VENTILATION — LOCKED IN PARTIAL OPEN POSITION BY RESTRICTOR).

WHILE DRAUGHT-PROOFING ADDRESSES AIR INFILTRATION (THE MOST SIGNIFICANT ENERGY LOSS FROM SASH WINDOWS), IT DOES NOT ADDRESS THE CONDUCTIVE HEAT LOSS THROUGH THE SINGLE GLASS ITSELF (U-VALUE OF ORIGINAL SINGLE GLASS: 5.0-5.6 W/M²K). FOR THE MOST SIGNIFICANT THERMAL AND ACOUSTIC PERFORMANCE IMPROVEMENT WITHOUT REPLACING THE ORIGINAL SASH WINDOWS, SECONDARY GLAZING IS THE RECOMMENDED APPROACH FOR LONDON VICTORIAN TERRACES.

SELECTAGLAZE SECONDARY GLAZING (THE UK MARKET LEADER IN HERITAGE SECONDARY GLAZING — USED BY ENGLISH HERITAGE, NATIONAL TRUST, AND LONDON CONSERVATION AREA PROPERTIES): SELECTAGLAZE SERIES 10 (LIFT-OUT PANEL — HINGED UPWARD TO OPEN — THE MOST BASIC SYSTEM): FOR FIXED LIGHTS OR WINDOWS WHERE OPENING IS INFREQUENT. SELECTAGLAZE SERIES 20 (HORIZONTAL SLIDING SECONDARY SASH — 2 PANELS THAT SLIDE HORIZONTALLY IN ALUMINIUM FRAME — MIRRORS THE OPERATION OF THE EXISTING SASH BELOW): THE MOST COMMON SELECTAGLAZE SYSTEM FOR LONDON VICTORIAN TERRACE SASH WINDOWS — ALLOWS OPERATION OF BOTH THE ORIGINAL SASH AND THE SECONDARY PANEL FOR VENTILATION. SELECTAGLAZE SERIES 41 (VERTICAL SLIDING SECONDARY SASH — MATCHES THE ORIGINAL SASH WINDOW OPERATION — THE SECONDARY PANEL SLIDES VERTICALLY TO OPEN): THE MOST AUTHENTIC-OPERATING SECONDARY GLAZING SYSTEM FOR VICTORIAN SASH WINDOWS — EXPENSIVE BUT SEAMLESS IN OPERATION.

ACOUSTIC GLASS OPTIONS FOR SECONDARY GLAZING: THE PERFORMANCE ADVANTAGE OF SECONDARY GLAZING OVER DOUBLE GLAZING IS MOST PRONOUNCED IN ACOUSTIC PERFORMANCE — THE AIR GAP BETWEEN THE PRIMARY SASH AND THE SECONDARY PANEL (TYPICALLY 100-200MM) ACTS AS A RESONANCE DECOUPLER. PILKINGTON OPTIPHON 6.4MM ACOUSTIC LAMINATE (6MM + 0.8MM PVB + 6MM — USED IN SECONDARY GLAZING FOR MAXIMUM NOISE REDUCTION): SECONDARY GLAZING WITH OPTIPHON GLASS AND 100MM+ GAP ACHIEVES RW 45-50DB — SIGNIFICANTLY BETTER THAN DOUBLE GLAZING (TYPICALLY RW 28-32DB). SUITABLE FOR LONDON VICTORIAN TERRACES ON BUSY ROADS (A ROADS, WITHIN 200M OF RAILWAYS OR TUBE LINES — A SIGNIFICANT PROPORTION OF LONDON VICTORIAN TERRACES).

SASH WINDOW DRAUGHT-PROOFING AND REFURBISHMENT COSTS IN LONDON VARY BY SCOPE — FROM DIY DRAUGHT-PROOFING WITH REDDISEALS KITS (APPROXIMATELY £30-60 PER WINDOW DIY MATERIALS) TO FULL PROFESSIONAL REFURBISHMENT WITH SECONDARY GLAZING (£800-2,500+ PER WINDOW INCLUDING SECONDARY GLAZING).

DIY DRAUGHT-PROOFING (REDDISEALS SASH WINDOW DRAUGHT PROOFING KIT — AVAILABLE ONLINE): MATERIALS PER WINDOW (PILE STRIPS, FOAM COMPRESSOR, MEETING RAIL SEAL): £30 TO £60. TOOLS REQUIRED: ROUTER OR REDDISEALS ROUTING MACHINE (AVAILABLE TO HIRE — £40-80/DAY). TIME: 3-4 HOURS PER WINDOW FOR AN EXPERIENCED DIY OPERATIVE. NOTE: REDDISEALS ROUTING MACHINE IS THE CRITICAL TOOL — WITHOUT THE CORRECT MACHINE, ACHIEVING A NEAT KERF OF EXACTLY THE RIGHT DEPTH AND WIDTH IS DIFFICULT.

PROFESSIONAL SASH WINDOW DRAUGHT-PROOFING (SPECIALIST CONTRACTOR — LONDON): COST PER WINDOW (DRAUGHT-PROOFING ONLY — SEALS ONLY, NO SASH CORD OR PULLEY WORK): £80 TO £200 PER WINDOW. A TYPICAL 3-BED LONDON VICTORIAN TERRACE (4-6 WINDOWS): £320 TO £1,200.

FULL SASH WINDOW REFURBISHMENT (PROFESSIONAL — REMOVE SASHES, REPLACE CORDS, PULLEYS, PARTING BEAD, DRAUGHT-PROOF, REFIT — PER WINDOW — LONDON): COST PER WINDOW: £250 TO £600. INCLUDES: CORD REPLACEMENT, PULLEY REPLACEMENT, PARTING BEAD REPLACEMENT, FULL DRAUGHT-PROOFING, REFIT AND ADJUST. 3-BED LONDON VICTORIAN TERRACE (4-6 WINDOWS): £1,000 TO £3,600.

SECONDARY GLAZING (SELECTAGLAZE SERIES 20 HORIZONTAL SLIDING — PER WINDOW — SUPPLY AND FIT): STANDARD CLEAR 6MM GLASS: £300 TO £600 PER WINDOW. ACOUSTIC GLASS (PILKINGTON OPTIPHON 6.4MM): ADD £50 TO £150 PER WINDOW FOR ACOUSTIC UPGRADE. COMBINED REFURBISHMENT + SECONDARY GLAZING (PER WINDOW): £550 TO £1,250.