uPVC Sash vs Timber Sash Windows: Which Is Right for Your Home?

In most conservation areas, uPVC sash windows are not approved. However, a growing number of planning authorities now accept high-specification flush-fit uPVC designs with mechanical joints, accurate profile replication, and woodgrain finishes. Always submit a pre-application enquiry to your local planning department with product literature and cross-section details before ordering.

uPVC sash windows typically last 25-30 years before the profiles begin to degrade and hardware fails. Timber sash windows last 40-60+ years with proper maintenance — and original Georgian and Victorian sash windows have lasted 150-200+ years, demonstrating the extraordinary longevity potential of quality timber. The key difference is that timber can be repaired and restored repeatedly, while uPVC generally cannot.

From 3-5 metres away, modern uPVC sash windows with woodgrain foil finishes look convincing. Up close, the wider profiles (100-120mm vs 55-70mm for timber), welded corner joints, and surface texture give them away. On a modern property where period authenticity is not expected, they look perfectly appropriate. On a Victorian or Georgian property, the differences are more jarring to a discerning eye.

Sash horns are the small projections at the bottom of the upper sash, originally a structural feature that strengthened the joint when wider glass panes replaced smaller Georgian glazing bars. On authentic timber sash windows, the horn is formed by extending the stile (vertical member) past the bottom rail — a 'run-through' horn. uPVC sash windows typically have moulded-on horns that are cosmetic rather than structural. Conservation officers can often identify uPVC windows by this detail.

Tilt-in cleaning mechanisms are available on some modern timber sash window designs, but they are uncommon and add complexity and cost. Most timber sash windows are cleaned from outside using a ladder, from inside by reaching out, or by removing the sashes (which is straightforward on traditional weight-and-pulley windows). If easy cleaning is a priority, this is a genuine advantage of uPVC.

Both can achieve high security ratings. Modern uPVC sash windows typically come with multi-point locking systems and can be specified to PAS 24 security standards. Timber sash windows can be fitted with sash locks, sash stops, and key-locking fitch fasteners. Both materials can accommodate laminated or toughened safety glass. Security performance depends more on the locking hardware than the frame material.

uPVC sash windows are available in white, cream, grey, black, and various woodgrain foil finishes (light oak, rosewood, Irish oak, etc.). Dual-colour options (different colours inside and outside) are common. Timber sash windows can be finished in any RAL colour using microporous paint, or in natural stains and oils that showcase the wood grain. Timber offers virtually unlimited colour choice, while uPVC is limited to the manufacturer's foil range.

Regular maintenance includes: checking and touching up paintwork annually (especially on exposed south and west elevations), repainting fully every 5-10 years, lubricating sash mechanisms and pulleys annually, checking sash cords for wear, clearing drainage channels and weep holes, and addressing any timber damage promptly before rot can spread. A well-maintained timber sash window can last 60+ years.

A flush-fit sash window has the sash sitting flush with the outer frame, replicating the appearance of a traditional timber sash window. A storm-proof design has the sash protruding slightly from the frame, which is more weatherproof but less authentic-looking. Flush-fit designs are more expensive but significantly more convincing as period-style replicas and stand a better chance of gaining conservation area approval.

Yes, this is sometimes possible if the box frame is in good condition. New sashes — either timber or in some cases uPVC — can be fitted into existing frames. However, the frames must be structurally sound, square, and capable of accepting the new sashes with appropriate draught-proofing. This approach can save money and preserve more of the original fabric, but it requires careful assessment by a specialist.