Window Styles: Casement, Sash, Tilt & Turn

Choosing the right window style affects your home’s appearance, energy performance, ease of cleaning, and ventilation. The most common types in UK homes, casement, sash, tilt-and-turn, and bay, each suit different building types and uses. Prices range from around £300 per casement unit to over £2,000 for a bespoke timber sash, supply and fit.

Casement Windows

The default choice for most UK new-build and replacement projects. A casement window has one or more panes hinged at the side (or top, when called an awning or top-hung casement) and opens outward on a friction-stay hinge. Most modern casements are side-hung; a fixed pane can sit beside the opening sash.

Best for: post-war housing, new builds, contemporary homes, and any property where cleaning and ventilation take priority over period aesthetics.

Casement subtypes

• Side-hung casement, opens from a side hinge; the most common UK type.
• Top-hung casement, hinged at the top; opens outward from the bottom; ideal for restricted ceiling heights or rooms where full reach to the handle is difficult.
• French casement, paired doors (no centre post); wide opening but reduced draught-proofing unless fitted with espagnolette locks.
• Tilt-before-turn (tilt-first), see tilt-and-turn section below.

Typical cost (supply & fit): £300–£900 per unit in uPVC; £500–£1,400 in aluminium; £700–£2,000 in timber.

Sash Windows

Sash windows are the defining feature of Georgian, Victorian, and Edwardian terraces. Two sashes (frames) slide vertically in channels, traditionally counterbalanced by cast-iron (sometimes lead) weights on cords; modern versions use spiral balances or constant-force springs.

Best for: period properties (pre-1920 housing), conservation areas, listed buildings, and anywhere the streetscape character depends on the original window style.

Box sash vs. spring-balanced

• Box sash (weights): traditional timber frame with a hollow box housing cast-iron or lead weights. Authentic for listed and conservation-area properties; requires specialist joinery skills to maintain.
• Spring-balanced sash: thinner frame, easier to manufacture in uPVC or aluminium; suitable for most period replacement projects where full authenticity isn’t essential.

Tilt-clean facility

Most modern sash windows allow the sashes to tilt inward for cleaning, an important feature if the window is above ground-floor level.

Typical cost (supply & fit):

• uPVC spring-balanced sash: £600–£1,200 per unit¹ (2016 price, brought to 2026)
• Aluminium sash: £900–£1,800 per unit
• Timber box sash (full replacement, double glazed): £2,100–£3,400 per unit²
• Overhaul and draught-proofing of an existing timber box sash: £330–£590 per window³

Tilt-and-Turn Windows

Popular in continental Europe and increasingly common in the UK, tilt-and-turn windows open in two ways: tilt inward from the top for background ventilation (common in the UK as “secure ventilation”), or swing inward fully from the side for cleaning and maximum airflow.

Best for: upper-floor rooms, flats (where outward opening risks passers-by), and any space where cleaning access is difficult from outside.

• Security advantage: the tilt position provides ventilation without creating a climbable opening, suitable for ground-floor use while you’re in the room.
• Cleaning: the inward-opening action makes window cleaning straightforward from inside.
• Draught performance: the sash is pulled onto compression seals at several locking points around the frame, which typically gives good draught and acoustic performance.

Typical cost (supply & fit): £400–£1,000 per unit in uPVC; £700–£1,600 in aluminium.

Bay Windows

A bay projects outward from the main wall in three or more planes. Structural bays require a lintel or corbelled brickwork; shallow bow windows curve in a gentle arc. Common in Victorian semis and detached houses of the Edwardian and interwar periods.

• Bay windows are usually a combination of fixed and opening casements or sashes.
• Replacement requires careful measurement of the angle at each corner (typically 90°, 135°, or 120°).
• Structural implications (lintel condition, foundation depth) must be assessed before replacement.

Typical cost (supply & fit): £1,200–£4,000 for a standard three-section bay in uPVC; significantly more for aluminium or timber.

Fixed Windows (Picture Windows)

Non-opening panes used where ventilation is provided elsewhere. Offer maximum thermal performance (no seal gaps around the opener) and maximum glazing area. Common above large sliding or bi-fold door systems.

Typical cost (supply & fit): £200–£600 per unit in uPVC.

Window Style Comparison Table

Materials

uPVC, the market leader for replacement windows. Low maintenance, thermally efficient, and competitively priced. Profile quality varies: look for multi-chambered sections and at least a 28 mm double-glazed unit; triple-glazed units are worth specifying in north-facing or exposed locations.

Aluminium, slim sightlines, any RAL colour, 40+ year lifespan. Thermally broken frames are essential to prevent cold bridging and to reach the 1.4 W/m²K that Part L sets for a replacement window. Higher cost than uPVC but increasingly chosen for contemporary properties.

Timber, usually expected for listed buildings and many conservation-area properties. Softwood (pine, redwood) is cheaper; hardwood (oak, meranti) is more durable. Requires painting or staining every 5–10 years. Accoya, a softwood modified by acetylation with acetic anhydride, offers exceptional dimensional stability, and its maker gives warranties of up to 50 years.⁴

Timber-aluminium composite, timber internally (for warmth and aesthetics), aluminium cladding externally (for weather resistance). Premium product; common in Scandinavian-specification builds.

Glazing Specifications

Under Part L of the Building Regulations (England), replacement windows in existing dwellings must achieve a whole-window U-value of 1.4 W/m²K or better (or a window energy rating of Band B minimum).⁵

• Double-glazed (4/16/4 with argon, low-e coating): U-value around 1.2–1.4 W/m²K, meets regs.
• Triple-glazed (4/16/4/16/4): U-value 0.7–1.0 W/m²K, worth specifying for north-facing rooms, noise-sensitive locations, or Passivhaus-standard projects.
• Acoustic glazing: asymmetric panes (e.g. 6/12/10) reduce sound transmission; worth considering near busy roads, railways or flight paths.

Choosing the Right Style

1. Match the original style where possible, a Victorian terrace looks wrong with tilt-and-turn. Check if you’re in a conservation area (special conditions apply).
2. Consider first-floor cleaning access, tilt-and-turn or top-hung casements save the cost of hiring a window cleaner.
3. Ventilation requirements, if the existing windows have background ventilators, Approved Document F says the replacement windows should include them too, no smaller than the originals.⁶ If they had none, the ventilation must be left no worse than before, which is usually met by fitting trickle vents of at least 8000 mm² equivalent area in each habitable room.⁶
4. Budget, uPVC casements are the most affordable; timber sashes the most expensive. Aluminium offers a strong mid-to-premium option.
5. Listed building or conservation area, if your house is listed, or is in a conservation area covered by an Article 4 Direction, you are likely to need consent to alter its windows, so consult your local planning authority before ordering.⁷ Timber vertical sliders in the original style are often required.
6. Escape windows, where an upper-floor window serves as an escape route in a fire, its replacement should provide at least the same potential for escape.⁸ An escape window needs an unobstructed openable area of at least 0.33 m², at least 450 mm high and 450 mm wide, with the bottom of the opening no more than 1100 mm above the floor.⁸

The rules in this note are those that apply in England. Scotland, Wales and Northern Ireland have their own building standards and permitted development rights.