Sash Window Renovation and Repair for London Victorian Terraces

THE TRADITIONAL VICTORIAN VERTICAL SLIDING SASH WINDOW (ALSO CALLED A SINGLE-HUNG OR DOUBLE-HUNG SASH WINDOW — MOST LONDON VICTORIAN TERRACES HAVE DOUBLE-HUNG SASH WINDOWS WHERE BOTH THE UPPER AND LOWER SASH CAN SLIDE VERTICALLY — BALANCED BY CAST IRON WEIGHTS RUNNING IN VERTICAL POCKETS ON EACH SIDE OF THE FRAME) CONSISTS OF THE FOLLOWING MAIN ELEMENTS THAT THE REPAIR AND RENOVATION CONTRACTOR MUST UNDERSTAND.

FRAME (OUTER FRAME — THE FIXED ELEMENT — COMPRISES): PULLEY STILE (THE VERTICAL MEMBER ON EACH SIDE OF THE FRAME — THE SASH CORD PASSES OVER A CAST IRON PULLEY AT THE TOP OF EACH PULLEY STILE AND DOWN INTO THE WEIGHT POCKET BELOW — THE PULLEY IS A SMALL CAST IRON WHEEL RECESSED INTO THE PULLEY STILE — A COMMON SOURCE OF FAILURE IS A SEIZED PULLEY THAT GRINDS OR STICKS AS THE CORD PASSES OVER IT); PARTING BEAD (A THIN NARROW TIMBER BEAD RUNNING VERTICALLY IN THE PULLEY STILE GROOVE THAT SEPARATES THE UPPER AND LOWER SASH — THE PARTING BEAD KEEPS THE TWO SASHES IN THEIR SEPARATE PARALLEL PLANES AS THEY SLIDE); STAFF BEAD (ALSO CALLED INNER BEAD OR STOP BEAD — THE INNERMOST VERTICAL BEAD ON EACH SIDE OF THE FRAME — RETAINS THE LOWER SASH IN THE FRAME — HELD BY SMALL OVAL WIRE NAILS AND CAN BE CAREFULLY REMOVED WITH A THIN BLADE TO RELEASE THE LOWER SASH FROM THE FRAME WITHOUT DAMAGING THE FRAME); WEIGHT POCKETS (THE VERTICAL CAVITIES ON EACH SIDE OF THE FRAME — INSIDE THE PULLEY STILE — CONTAINING THE CAST IRON WEIGHTS THAT COUNTERBALANCE THE SASH — ACCESS IS VIA A POCKET PIECE — A SMALL REMOVABLE PANEL IN THE BOTTOM OF EACH PULLEY STILE); SILL (THE HORIZONTAL BOTTOM MEMBER OF THE OUTER FRAME — SLOPED OUTWARD FOR DRAINAGE — TYPICALLY PAINTED SOFTWOOD OR HARDWOOD — A COMMON SITE OF WET ROT); HEAD (THE HORIZONTAL UPPER MEMBER OF THE OUTER FRAME); CASED FRAME (THE COMPLETE ASSEMBLED OUTER FRAME INCLUDING THE WEIGHT POCKETS — SO CALLED BECAUSE THE WEIGHTS ARE 'CASED' INSIDE THE FRAME); SASH (THE MOVING ELEMENT — THE GLAZED PANEL THAT SLIDES VERTICALLY — A DOUBLE-HUNG WINDOW HAS AN UPPER SASH (SLIDING IN THE OUTER TRACK) AND A LOWER SASH (SLIDING IN THE INNER TRACK)): TOP RAIL (UPPER HORIZONTAL MEMBER OF THE SASH — THE MEETING RAIL OF THE UPPER SASH); BOTTOM RAIL (LOWER HORIZONTAL MEMBER OF THE SASH); MEETING RAILS (THE CENTRE HORIZONTAL MEMBERS — UPPER SASH MEETING RAIL AND LOWER SASH MEETING RAIL MEET IN THE MIDDLE WHEN BOTH SASHES ARE CLOSED — THE POINT OF GREATEST DRAUGHT LOSS IN THE ORIGINAL UNRESTORED SASH WINDOW); GLAZING BARS (THIN TIMBER MEMBERS DIVIDING THE SASH INTO MULTIPLE SMALLER PANES — ON MOST LONDON VICTORIAN TERRACES 2-OVER-2 (TWO PANES EACH SASH — TYPICAL FOR LATE VICTORIAN TERRACES 1880S-1900S) OR 6-OVER-6 (SIX PANES EACH SASH — MORE COMMON ON EARLIER GEORGIAN AND EARLY VICTORIAN PROPERTIES 1820S-1850S)).

THE FOLLOWING DEFECTS ARE MOST COMMONLY FOUND IN THE ORIGINAL SASH WINDOWS OF LONDON VICTORIAN TERRACES AND ARE ADDRESSABLE WITHOUT REPLACING THE WINDOWS: BROKEN OR ROTTEN SASH CORD (THE MOST COMMON MECHANICAL DEFECT — THE COTTON OR LINEN WOVEN CORD THAT CONNECTS THE SASH TO THE COUNTERBALANCE WEIGHTS): SYMPTOMS: SASH WILL NOT STAY OPEN IN ANY POSITION (DROPS OR WILL NOT STAY UP), SASH IS DIFFICULT TO SLIDE (BECAUSE THE CORD IS FRAYED AND CATCHING), SASH IS NOT BALANCED (ONE SIDE HAS A BROKEN CORD — THE SASH TILTS TO THE SIDE WITH THE WORKING CORD); REPAIR: REMOVE THE STAFF BEAD ON THE AFFECTED SIDE — REMOVE THE LOWER SASH FROM THE FRAME — ACCESS THE WEIGHT POCKET (REMOVE POCKET PIECE AT BOTTOM OF PULLEY STILE) — RETRIEVE THE WEIGHT — THREAD NEW SASH CORD (HESSIAN-BONDED COTTON OR POLYPROPYLENE REPLACEMENT CORD — 9MM OR 10MM DIAMETER — WRIGHT'S SASH CORD OR PROCTOR SASH CORD) OVER THE CAST IRON PULLEY AND DOWN INTO THE WEIGHT POCKET — TIE NEW CORD TO WEIGHT — THREAD OTHER END OF CORD THROUGH THE GROOVE IN THE SASH SIDE — FIX WITH THREE 30MM GALVANISED CLOUT NAILS AT EQUAL INTERVALS INTO THE GROOVE FACE; ROTTEN TIMBER ON SILL, BOTTOM RAIL, OR OTHER ELEMENTS (WET ROT — MOST COMMON IN THE SILL AND THE BOTTOM RAIL OF THE LOWER SASH — AREAS EXPOSED TO RAIN AND STANDING WATER): FOR LOCALISED SURFACE ROT: DRY OUT AFFECTED AREA — BRUSH ON BORA-CARE BORON CONSOLIDANT — APPLY RESIWOOD OR TIMBABUILD WOOD REPAIR COMPOUND (EPOXY FILLER) TO RESTORE PROFILE; FOR DEEPER STRUCTURAL ROT IN THE SILL: FULL SILL REPLACEMENT IS USUALLY MORE COST-EFFECTIVE — NEW HARDWOOD CILL (IDIGBO OR ACCOYA — ACCOYA (MODIFIED RADIATA PINE — ACETYLATED — DIMENSIONALLY STABLE AND ROT-RESISTANT) PREFERRED FOR SASH WINDOW REPLACEMENT SILLS IN A HERITAGE CONTEXT — BS 7359 COMPATIBILITY); PAINT FAILURE AND STICKING (SASH STUCK SHUT — PAINTED SHUT — COMMON IN PROPERTIES WHERE PERIODIC REPAINTING HAS OCCURRED WITHOUT FIRST RELEASING THE SASH AND PAINTING WITH THE SASH OPEN): RELEASE PAINTED-SHUT SASH BY RUNNING A STANLEY KNIFE BLADE AROUND THE PERIMETER OF THE SASH AT THE BEAD JUNCTION — GENTLY TAP WITH A RUBBER MALLET TO FREE — DO NOT LEVER AGGRESSIVELY AGAINST THE GLAZING BARS (RISK OF CRACKED GLASS OR SPLIT GLAZING BAR); PLANE SASH SIDES WHERE SWELLING HAS CAUSED STICKING — APPLY CANDLE WAX OR SILICONE SPRAY TO RUNNING SURFACES.

THE ORIGINAL UNRESTORED SASH WINDOW IS THE SINGLE LARGEST SOURCE OF DRAUGHT AND UNCONTROLLED VENTILATION HEAT LOSS IN MOST LONDON VICTORIAN TERRACES — A SINGLE UNRESTORED DOUBLE-HUNG SASH WINDOW CAN HAVE AN AIR INFILTRATION RATE EQUIVALENT TO LEAVING A SMALL CIRCULAR HOLE 25-30MM IN DIAMETER PERMANENTLY OPEN IN THE WALL — ACROSS A TYPICAL LONDON VICTORIAN TERRACE WITH 6-8 SASH WINDOWS, THE TOTAL DRAUGHT LOSS IS SIGNIFICANT.

TRADITIONAL SASH WINDOW DRAUGHT PROOFING (THE PROFESSIONAL SASH WINDOW RENOVATION APPROACH — ALSO CALLED 'PILE WEATHERSTRIP DRAUGHT PROOFING'): THE STANDARD PROFESSIONAL DRAUGHT PROOFING APPROACH USED BY SPECIALIST SASH WINDOW RESTORERS IN LONDON USES PILE WEATHERSTRIP (A POLYPROPYLENE PILE BRUSH — TYPICALLY 5MM HIGH AND 9MM WIDE PILE BLOCK — SUPPLIED IN ROLL FORM BY SPECIALIST SUPPLIERS INCLUDING VENTROLLA (UK LEADING SASH WINDOW DRAUGHT PROOFING SPECIALIST BASED IN HARROGATE) AND TOPMASTA): THE SASH IS REMOVED FROM THE FRAME — THE RUNNING SURFACES OF THE SASH AND FRAME ARE PLANED AND CLEANED — PILE WEATHERSTRIP IS ROUTED INTO A GROOVE CUT IN THE RUNNING SURFACES OF THE SASH SIDES (BOTH SIDES OF EACH SASH — UPPER SASH OUTER FACE + LOWER SASH INNER FACE) AND IN THE MEETING RAILS — PILE WEATHERSTRIP IS ALSO FITTED INTO A GROOVE ROUTED IN THE HEAD OF THE OUTER FRAME (TOP OF UPPER SASH) AND IN THE TOP OF THE LOWER SASH PARTING BEAD (THE BOTTOM OF THE LOWER SASH AGAINST THE SILL USES A FOAM COMPRESSIBLE SEAL OR A NEOPRENE SEAL); THE PILE WEATHERSTRIP FILLS THE GAP BETWEEN THE SASH AND THE FRAME AS THE SASH SLIDES — VIRTUALLY ELIMINATING THE AIR INFILTRATION THROUGH THE SASH SIDES AND MEETING RAILS — WHILE STILL ALLOWING THE SASH TO SLIDE FREELY; ALTERNATIVE DRAUGHT PROOFING (SELF-ADHESIVE FOAM STRIPS — THE DIY APPROACH — MUCH LESS EFFECTIVE AND LESS DURABLE THAN PILE WEATHERSTRIP): self-adhesive cellular foam strips (Draught Excluder Foam Tape — available from B&Q, Wickes — compressible foam — push the sash against the foam to seal the gap) — less effective than pile weatherstrip because foam compresses fully and allows the sash to stick — degrades over 2-5 years of opening/closing — NOT RECOMMENDED FOR REGULAR-USE SASH WINDOWS.

WHERE IMPROVING THE THERMAL PERFORMANCE OF ORIGINAL SASH WINDOWS IS A PRIORITY — AND WHERE REPLACEMENT WITH DOUBLE-GLAZED UNITS IS NOT PERMITTED OR NOT DESIRED — SECONDARY GLAZING (A SECOND PANE OR PANEL FITTED TO THE INNER FACE OF THE EXISTING SASH WINDOW FRAME) IS THE STANDARD HERITAGE-ACCEPTABLE APPROACH.

SECONDARY GLAZING TYPES FOR VICTORIAN SASH WINDOWS: (1) FIXED OR HINGED PANEL SECONDARY GLAZING (A SLIM ALUMINIUM OR TIMBER FRAME SECONDARY PANEL FITTED TO THE REVEAL INSIDE THE EXISTING SASH WINDOW — THE SECONDARY PANE IS SEALED TO THE REVEAL ON ALL FOUR SIDES — PROVIDES THE BEST THERMAL AND ACOUSTIC PERFORMANCE OF ALL SECONDARY GLAZING OPTIONS): BESPOKE SECONDARY GLAZING SUPPLIERS: SELECTAGLAZE (UK MARKET LEADER IN BESPOKE SECONDARY GLAZING — ROYAL WARRANT — RANGE: SERIES 10 CASEMENT/PIVOT, SERIES 41 LIFT-OUT PANEL, SERIES 35 HORIZONTAL SLIDING — ALL IN SLIM POWDER-COATED ALUMINIUM FRAME IN STANDARD COLOURS — WHITE, BROWN, GREY — BESPOKE COLOURS AVAILABLE); PILKINGTON SPACIA (6.4MM VACUUM GLAZING — 0.7 W/M²K U-VALUE — THINNEST SECONDARY GLAZING UNIT AVAILABLE — 6.4MM TOTAL THICKNESS (VS 16-28MM FOR A STANDARD DOUBLE-GLAZED UNIT) — FITS IN VERY NARROW REVEALS — THERMALLY EQUIVALENT TO A DOUBLE-GLAZED UNIT); (2) SLIM-FRAME SLIDING SECONDARY GLAZING (THE MOST COMMON FOR VICTORIAN SASH WINDOWS — THE SECONDARY GLAZING UNIT ITSELF SLIDES HORIZONTALLY TO ALLOW ACCESS TO THE ORIGINAL SASH BELOW FOR VENTILATION): SELECTAGLAZE SERIES 35 HORIZONTAL SLIDING — THE SECONDARY PANEL SLIDES ON STAINLESS STEEL TRACKS FIXED TO THE REVEAL — ACOUSTIC IMPROVEMENT: APPROXIMATELY 40 DB REDUCTION IN TRAFFIC NOISE (FROM APPROXIMATELY 70 DB TYPICAL LONDON STREET TO APPROXIMATELY 30 DB IN THE ROOM — A DRAMATIC IMPROVEMENT IN ACOUSTIC COMFORT FOR PROPERTIES ADJACENT TO BUSY LONDON ROADS); (3) MAGNETIC SECONDARY GLAZING (FRAMELESS THIN PANEL THAT SNAPS ONTO A MAGNETIC TAPE FRAME FITTED TO THE REVEAL — DIY INSTALLATION — LESS THERMALLY EFFECTIVE THAN FRAMED SECONDARY GLAZING BUT SUITABLE FOR CONSERVATION AREAS WHERE EVEN THE SLIM ALUMINIUM FRAME OF SELECTAGLAZE WOULD BE CONSIDERED INTRUSIVE): MAGNETITE SECONDARY GLAZING OR MHB MAGNETIC SECONDARY GLAZING — CLEAR ACRYLIC PANEL + MAGNETIC CHANNEL FIXED TO REVEAL — COST: APPROXIMATELY £100-200 PER WINDOW DIY.

SASH WINDOW RENOVATION AND DRAUGHT PROOFING COSTS FOR A LONDON VICTORIAN TERRACE (LONDON 2025 — APPROXIMATE RANGE — SPECIALIST SASH WINDOW RESTORATION CONTRACTOR): SASH CORD REPLACEMENT (PER SASH — SINGLE BROKEN CORD — REMOVE STAFF BEAD, ACCESS WEIGHT POCKET, FIT NEW CORD, REFIX BEAD): APPROXIMATELY £60-150 (PER SASH — SINGLE CORD — SPECIALIST CONTRACTOR); FULL SASH OVERHAUL (BOTH SASHES REMOVED, CLEANED, PLANED, NEW CORDS BOTH SIDES, RUNNING SURFACES WAX-TREATED, REPAIRED, REFIXED): APPROXIMATELY £150-350 (PER WINDOW — TWO SASHES — SPECIALIST CONTRACTOR); DRAUGHT PROOFING (PILE WEATHERSTRIP — PROFESSIONAL ROUTING AND FITTING — PER WINDOW — BOTH SASHES): APPROXIMATELY £150-300 (PER WINDOW — INCLUDING MEETING RAIL SEALS — SPECIALIST SASH WINDOW CONTRACTOR — VENTROLLA OR SIMILAR); FULL SASH RENOVATION + DRAUGHT PROOFING (OVERHAUL + NEW CORDS BOTH SASHES + PILE WEATHERSTRIP ROUTING TO BOTH SASHES AND FRAME — PER WINDOW): APPROXIMATELY £250-500 (PER WINDOW — SPECIALIST CONTRACTOR); SILL REPLACEMENT (FULL REPLACEMENT OF ROTTEN WINDOW SILL — NEW ACCOYA OR HARDWOOD CILL — SUPPLY AND FIT — PER WINDOW): APPROXIMATELY £350-700 (PER WINDOW — INCLUDING JOINERY, FITTING, AND DECORATION); SECONDARY GLAZING (SUPPLY AND FIT — PER WINDOW): DIY MAGNETIC SECONDARY GLAZING: APPROXIMATELY £100-200 (PER WINDOW); SELECTAGLAZE BESPOKE SECONDARY GLAZING (FRAMED — SLIDING OR HINGED — SUPPLY AND FIT): APPROXIMATELY £300-700 (PER WINDOW — STANDARD SIZE — CUSTOM SIZES MORE); PILKINGTON SPACIA VACUUM GLAZING SECONDARY PANEL: APPROXIMATELY £500-1,000+ (PER WINDOW — BESPOKE SIZE — SPECIALIST SUPPLY AND FIT); TYPICAL FULL SASH WINDOW RENOVATION PROGRAMME — LONDON VICTORIAN TERRACE 6 WINDOWS (FULL OVERHAUL + CORDS + DRAUGHT PROOFING + SECONDARY GLAZING): APPROXIMATELY £3,000-6,000 (FULL PROGRAMME — SELECTAGLAZE SECONDARY GLAZING — SPECIALIST CONTRACTOR — EXCLUDES REDECORATION); UPVC REPLACEMENT SASH WINDOW (SLIDING SASH UPVC — DECEUNINCK OU REHAU — NOT ORIGINAL SLIDING SASH — SIGNIFICANTLY LESS APPROPRIATE FOR A CONSERVATION AREA VICTORIAN TERRACE): APPROXIMATELY £600-1,200 PER WINDOW SUPPLY AND FIT — NOTE: NOT PERMITTED IN MANY LONDON CONSERVATION AREAS.