London is renowned for its beautiful historic architecture, with sash windows being a quintessential feature in many period buildings. As both a functional and decorative element, preserving original sash windows is important for maintaining the aesthetic character of buildings.
However, as a moving part constantly exposed to the elements, sash windows require regular maintenance and care to keep them functioning properly and prevent deterioration.

This article provides tips on maintaining traditional sash windows to keep these architectural gems in good working order.

Regular Cleaning and Inspection

A key part of sash window maintenance is regular cleaning, at least twice a year. This removes built-up dirt and grime which can damage window components and cause decay. Use a soft brush and mild detergent, avoiding abrasive cleaners which could scratch the glass or wood. Pay close attention to friction points where two surfaces rub together, cleaning out any debris which could impede operation.

When cleaning, inspect all window components for signs of wear, damage, or rot. Check that the sash cords and pulleys operate smoothly and are not frayed or aged. Ensure counterbalance weights can move freely within the weight channels. Any issues detected early can be quickly addressed before major repairs are needed.

Re-paint and Re-putty Frames

LBS mentioned that painting sash window frames helps protect the wood from moisture damage. Re-paint every 2-3 years, ensuring to properly prepare surfaces by scraping away old paint and sanding smooth. Use a high-quality exterior paint formulated for woodwork. If the existing paint is peeled, cracked or blistering, complete paint removal and re-priming may be required prior to repainting.
Check putty sealant around window panes annually. Repair or replace any cracked or missing glazing putty to prevent air and water infiltration. Carefully remove old putty with a putty knife, apply new putty, then paint over for a neat finish. Use linseed oil putty for a flexible, long-lasting seal.

Reglaze Window Panes

Sash window panes can become loose or damaged over time. Replace any cracked, broken, or missing panes to maintain energy efficiency and security. Select new glass to match original panes, whether modern float glass or period cylinder glass. Remove old putty, carefully pry out existing panes, seat the replacement pane and re-putty the perimeter. Let cure before painting over glazing putty. Consider professional reglazing for valuable antique glass.

Repair or Replace Sash Cords

The sash cords which raise and lower the sashes are a high-wear item. Check cords annually and replace any which are frayed, stretched, or broken. It's advisable to replace cords in pairs on a sash for balanced operation. Remove staff bead or parting strip to access cords, detach sash weights, then detach and replace worn cords. Use durable braided sash cord in the correct thickness and length.

Address Loose Sash Joints

Old sash joints can become loose over time, causing the sashes to slip within the frame. This allows air infiltration and reduces window operation. Tighten loose joints using shims and wood splines along the length of the joint - tap splines in with a hammer and small block. Where joint movement is severe, professional sash replacement may be required.

Replace Broken Sash Chains

Counterbalance weights rely on chains or ropes running within vertical channels. If these break, the weights will no longer stabilise the sashes. Replace broken chains as soon as possible to avoid damage or sagging. Detach the weights, feed new chain over the pulley then re-attach weights. Use galvanized or stainless-steel chain to resist corrosion.

Draught Proof Sashes

Poorly fitted sash windows often have gaps which allow draughts, air leakage and energy loss. Draught proof sashes by installing brush or fin seals to the vertical and horizontal rails or consider secondary glazing systems. Compress seals when closing the windows to form an air tight barrier. Draught proofing improves comfort and energy efficiency.

Refurbish Tilt Mechanisms

Sash windows which operate on a tilt function can have mechanisms that wear down over time. Refurbish tilt latches and hinges to restore smooth operation when tilting sashes inwards for cleaning. Replace worn latch barrels and strike plates so the latches engage securely. Lubricate hinges with a penetrating oil and tighten any loose screws.

Protect Friction Points

The intersection where sash cords cross over on the pulley, and where sash rails meet, are key friction points. Protect them by regularly applying lubricant to prevent excessive wear and abrasion damage. Use a silicone or beeswax based lubricant suitable for wood and sash materials. Maintain protective paint finishes over vulnerable intersection points.

Clear Sash Channels

Build-up of dirt, debris and paint flecks within sash weight channels can impede weights moving freely. Carefully vacuum channels to clear any accumulation. If paint build up form’s 'bridges' across channels, these will need to be carefully scraped out without damaging the surrounding wood. Keeping channels clean allows cords and weights to operate smoothly.

Ease Sticking Sashes

Sash windows should slide up and down smoothly when operated. Sticking can result from multiple causes like paint build up, wood expansion or misaligned frames. Sticking sashes should be eased not forced. Planning high points, lubricating friction points, adjusting frames and stripping paint can help improve operation. Severe sticking may require professional intervention.

Repair Rot and Decay

Untreated rot and wood decay is detrimental to sash windows and can spread if left unchecked. Cut out any soft, crumbly sections and repair with a suitable epoxy wood filler or Dutchmen inserts. Sand, prime and paint repaired areas. Severe deterioration may necessitate partial or full sash replacement. Keep older windows well painted to minimise moisture damage.

Final words

With the right maintenance approach, London's treasured sash windows can provide smooth operation and enhance building aesthetics for decades to come. Following these tips will help preserve these architectural gems in good condition.