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Bay vs Bow Windows: Complete Comparison Guide for UK Homeowners
Our Verdict
Bay windows are the more practical and affordable choice for most UK homes, offering excellent natural light and a classic angular profile from around £1,500. Bow windows command a premium but deliver an elegant curved aesthetic that adds genuine architectural distinction, making them ideal for period properties or homeowners seeking a statement feature.
At a Glance
Bay Windows
Key Specs
- Typically 3 panels at 90° or 135° angles
- Projects 300-600mm from the wall
- Available in uPVC, timber and aluminium
- U-value from 1.2 W/m²K (double glazed)
Bow Windows
Key Specs
- Typically 4-6 panels in a gentle arc
- Projects 200-500mm from the wall
- Available in uPVC, timber and aluminium
- U-value from 1.2 W/m²K (double glazed)
Detailed Comparison
| Feature | Bay Windows | Bow Windows |
|---|---|---|
| Typical Cost (installed) | £1,500-£3,500 | £2,000-£4,500 |
| Number of Panels | 3 panels | 4-6 panels |
| Shape | Angled / geometric | Curved / arc |
| Wall Projection | 300-600mm | 200-500mm |
| Interior Space Gained | More usable floor space | Less floor space due to curve |
| Natural Light | Excellent from 3 directions | Excellent panoramic spread |
| Structural Support | Requires lintel or gallows brackets | Requires lintel or gallows brackets |
| Planning Permission | Usually not required (like-for-like) | Usually not required (like-for-like) |
| Installation Time | 2-3 days | 3-5 days |
| Best Suited Property | Victorian terraces, semi-detached | Edwardian, detached, period homes |
| Window Seat Potential | Excellent – flat base easy to furnish | Good – curved seat is more complex |
| Ventilation Options | Side panels open as casements | Multiple opening panels available |
| Energy Efficiency (double glazed) | U-value ~1.4 W/m²K | U-value ~1.4 W/m²K |
| Maintenance | Standard – fewer joints | Higher – more joints and seals |
Choose Bay Windows If...
- You want to maximise usable interior floor space with a practical alcove
- Your property is a Victorian or Edwardian terrace where bay windows are architecturally appropriate
- Budget is a priority — bay windows cost 25-35% less than equivalent bow windows
- You plan to install a window seat, desk or storage in the bay recess
Choose Bow Windows If...
- You prefer a softer, curved aesthetic that adds elegance to a detached property
- Your home originally featured bow windows and you want a faithful replacement
- You have a wider wall opening that can accommodate the gentle arc of a bow design
- Panoramic views are a priority and you want light distributed evenly across the curve
Cost Comparison
A standard three-panel uPVC bay window with double glazing typically costs £1,500-£2,200 fully installed in the UK. Upgrading to timber increases this to £2,500-£3,500. Bow windows start at around £2,000 for a four-panel uPVC unit and rise to £3,500-£4,500 for timber or aluminium options with more panels. Both window types may incur additional structural costs of £300-£800 for lintels, gallows brackets or platform construction if existing supports are inadequate. Planning application fees (approximately £206 in England) may apply if the window change alters the external appearance in a conservation area. Over a 20-year lifespan, maintenance costs are comparable for uPVC versions of both types, but timber bow windows will require more frequent repainting due to the greater number of joints and exposed surfaces.
Frequently Asked Questions
Like-for-like replacements generally fall under permitted development and do not require planning permission. However, if you are changing from one type to the other, increasing the projection, or your property is in a conservation area or is listed, you should check with your local planning authority before proceeding.
Both add value by increasing natural light and kerb appeal. Estate agents suggest projecting windows can boost property value by 5-10%. Bay windows offer a stronger return on investment due to their lower initial cost, but a well-executed bow window on a suitable property can be equally impactful.
Yes, but it involves significant structural work. The existing opening may need widening to accommodate the bow's gentle curve, and the lintel and supporting structure will likely need replacing. Budget £3,000-£6,000 for a full conversion including making good internally and externally.
Yes, the curved track required for bow window curtains or blinds costs more than a standard straight or angled bay track. Expect to pay £150-£400 for a curved curtain track compared with £50-£150 for a bay window track. Roller blinds are often fitted per panel, which adds up with four to six panels in a bow.
uPVC bay and bow windows typically last 20-30 years. Timber versions can last 40-60 years or more with proper maintenance, including repainting every 5-8 years. Aluminium frames have an expected lifespan of 30-45 years with minimal upkeep.
Poorly installed or maintained projecting windows of either type can allow water ingress at the junction with the wall. Ensuring proper flashing, sealant and drainage at the roof of the bay or bow is critical. Regular inspection and resealing every few years will prevent damp issues.
Both options are available. A flat roof (typically lead or GRP fibreglass) is the most common and affordable option for bay windows. A pitched or hipped roof adds character and can improve rainwater runoff but costs an additional £500-£1,500. Bow windows almost always use a curved or flat roof detail.
Bay and bow windows can lose slightly more heat than flat windows because they project beyond the insulated wall and have more exposed surface area. However, modern double or triple glazing with low-E coatings and argon gas fills minimises this effect. Ensuring the roof and floor of the bay are properly insulated is equally important.
A square bay window has side panels set at 90° to the front panel, creating a box-like projection. It is most commonly found on Victorian properties in the UK and offers the maximum interior floor space of any projecting window style.
Yes, but this counts as an alteration to the external appearance and will usually require planning permission. Structural work is needed to support the new projection, including a lintel, foundation or corbels, and roof structure. Costs typically range from £3,000-£6,000 depending on size and material.
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