Sash vs Casement Windows: Complete UK Comparison Guide

Generally no. Conservation area regulations typically require like-for-like replacement, meaning sash windows must be replaced with sash windows of similar appearance. You will need to apply for planning permission if you wish to change the window style, and this is frequently refused. Always check with your local planning authority before making any changes. Some councils publish specific guidance on acceptable window replacements for their conservation areas.

Modern sash windows are only marginally less energy efficient than casement windows. While casement windows can achieve slightly better U-values (from 1.2 W/m²K vs 1.4 W/m²K for sash), the real-world difference in energy costs is small — typically £20-£40 per year for an average home. Both types comfortably meet Building Regulations Part L requirements when double or triple glazed with low-E coatings and argon gas filling.

Timber sash windows, when well maintained, can last 60-100+ years — many original Victorian sash windows are still in use today. uPVC sash windows typically last 20-30 years. Casement windows have a similar lifespan by material: timber casements last 40-60 years, uPVC casements 20-30 years, and aluminium casements 30-45 years. The longevity of timber sash windows is one of their strongest selling points.

Modern casement windows are generally more secure out of the box due to their multi-point locking systems. However, modern sash windows can be fitted with advanced security hardware including PAS 24 compliant locks. Both types can achieve Secured by Design accreditation. If security is a concern, ensure whichever type you choose is PAS 24:2022 certified and carries the Secured by Design mark.

Yes, particularly on period properties. Estate agents estimate that appropriate sash windows can add 5-10% to the value of a Georgian, Victorian, or Edwardian property. Conversely, replacing original sash windows with casement windows can reduce value by a similar amount. In conservation areas, the presence of correct-style windows is even more important for property valuation.

Yes, uPVC sash windows are widely available and offer the traditional sash appearance at a significantly lower cost than timber. Modern uPVC sash windows feature authentic-looking run-through horns, slim sightlines, woodgrain foil finishes, and tilt-in sashes for easy cleaning. Prices range from £600 to £1,200 per window installed. However, they may not be acceptable in conservation areas where timber is often specified.

For a typical three-bedroom semi with 8-10 windows: uPVC casement windows cost £4,000-£7,000, uPVC sash windows cost £6,000-£12,000, timber casement windows cost £8,000-£16,000, and timber sash windows cost £12,000-£25,000. These prices include installation, VAT, and disposal of old windows. Costs vary by region, with London and the South East typically 15-20% higher than the national average.

Yes, casement windows are generally easier to clean because they open fully, giving you access to both sides of the glass from inside. Traditional sash windows require cleaning the outside from the exterior, which can be difficult on upper floors. However, modern sash windows often feature a tilt-in facility that allows both sashes to be tilted inward for safe cleaning from inside — a significant improvement over traditional designs.

Sash windows offer superior ventilation control. By opening both the top and bottom sashes, you create a natural convection current that efficiently circulates air without creating draughts. Casement windows provide ventilation through a single opening point and cannot replicate this dual-flow effect. For rooms where air quality and gentle ventilation are important, sash windows are the better choice.

If you use a FENSA-registered installer, they will self-certify the work and you do not need to apply separately for Building Regulations approval. If you use a non-FENSA installer, you must apply to your local authority for Building Control approval, which costs approximately £200-£400. All replacement windows must meet the thermal performance requirements of Building Regulations Part L, regardless of who installs them.