Bay windows and bow windows both project outward from your home’s exterior wall and from the street; they can look almost identical. But they are built differently, suit different properties, and come with different costs, planning rules, and design outcomes.
This guide cuts through the confusion. Below, you’ll find a clear comparison of both window types, the available styles, what each costs, and a simple checklist to help you decide which is right for your home.
Bay vs Bow Window at a Glance
| Bay Window | Bow Window | |
| Shape | Angular / polygonal | Curved / rounded |
| Panels | 3 panels | 4–6 panels |
| Panel angle | 30° or 45° | ~10° each |
| Min. wall space | ~40 inches | ~80 inches |
| Natural light | Good | Excellent |
| Planning permission | More likely required | Often not required |
| Cost | More affordable | ~1.5–2.5× more |
| Best for | Terraced / narrower homes | Wider / period homes |
What Is a Bay Window?
A bay window projects outward from the wall of a property. The brickwork beneath follows the same angular shape as the window, supporting its weight. This creates a small interior alcove — often used as a window seat, reading nook, or extra storage.
Key features:
• 3 panels: one large fixed center window + two angled side panels
• Side panels set at 30° or 45° from the main wall
• Angular, polygonal shape, clean and architectural
• Brickwork below mirrors the window’s projection
• Common in Victorian and Edwardian homes
• Creates usable floor space inside the room
What Is a Bow Window?
A bow window — also called a compass window — also projects from the wall, but forms a smooth, continuous curve rather than hard angles. The key difference: the brickwork beneath stays flat, meaning less structural disruption during installation.
Key features:
• 4 to 6 equal-sized panels, each at ~10° angles from one another
• Smooth, rounded silhouette — softer than a bay
• More glass panels = more natural light and wider views
• Flat brickwork below makes installation simpler
• Suits wider-fronted and period properties
Bay Window vs Bow Window: Key Differences
Shape and Appearance
•
• Bay: Angular with sharp 30–45° corners — bold, geometric, architectural
• Bow: Smooth curve at ~10° per joint — soft, elegant, flowing
Panels and Light
• Bay: 3 panels — good natural light through large centre pane
• Bow: 4–6 panels — significantly more glass = brighter room, panoramic views
Space Requirements
• Bay: Fits into ~40 inches of wall width — ideal for terraced houses
• Bow: Needs ~80 inches minimum — suits wider or detached properties
Interior Space
• Bay: Creates a defined alcove — perfect for a window seat or built-in bench
• Bow: Wider, shallower curve — feels like an extension of the room rather than a nook
Home Styles
• Bay: Victorian terraces, Edwardian semis, modern homes, cottages, narrower frontages
• Bow: Period properties, heritage homes, Georgian style, wider-fronted houses
Types of Bay Windows and Bow Windows
| Type | What It Is |
| Bay Window Types | |
| Canted Bay | The most common UK type — flat front with two angled side panels at 30° or 45°. Classic Victorian and Edwardian look. |
| Box Bay | Square-shaped with 90° side panels — clean, modern look. Popular in kitchens and new builds. |
| Oriel Window | Upper-floor only — projects from above ground level, supported by brackets. No ground-floor footprint change. |
| Victorian Bay | Ornate detailing, sash glazing bars, multi-pane glass. Defines millions of UK period terraces. |
| Modern Bay | Slim frames, large glass, minimal sightlines. Suits contemporary extensions and new builds. |
| Bow Window Types | |
| 4-Pane Bow | Smallest standard bow — moderate curve, good starting point for narrow-ish walls or flat-to-bow conversions. |
| 5-Pane Bow | Most popular choice — generous curve, excellent light, suits most living room openings. |
| 6-Pane Bow | Widest curve — dramatic, panoramic. Needs large wall opening (120+ inches). Best on wider detached homes. |
| Circle / Compass | Near-full semicircle, sometimes wrapping a corner. Bespoke, heritage-style installations. |
Bay Window vs Bow Window: Pros and Cons
Bay Window
| ✅ Pros | ❌ Cons |
| More affordable — lower materials and labour | Less natural light than a bow |
| Suits narrower walls (from ~40 inches) | More likely to require planning permission |
| Creates a defined alcove and window seat | Structural brickwork work required |
| Works across many home styles | May need a roof section above the projection |
| Easier to match existing period features |
Bow Window
| ✅ Pros | ❌ Cons |
| More natural light — more glass panels | Costs 1.5–2.5× more than a comparable bay |
| Panoramic, wider garden or street views | Requires wider wall space (~80 inches min.) |
| Flat brickwork = simpler, faster installation | More joints = more maintenance over time |
| Often falls under Permitted Development | Less defined interior alcove for seating |
| Softer look suits period and heritage homes |
Bay Window vs Bow Window Cost
Bow windows cost significantly more than bay windows — typically 1.5 to 2.5 times more. The main reasons: more glass panels, custom curved frames, and more complex installation.
| Window Type | Bay Window | Bow Window |
| uPVC | £800 – £1,800 | £1,500 – £3,500 |
| Timber | £1,500 – £3,500 | £2,500 – £5,500 |
| Aluminium | £1,800 – £4,000 | £3,000 – £6,500+ |
| Labour (approx.) | £300 – £700 | £500 – £1,200 |
Factors that affect the final price:
• Size of the window opening
• Material choice: uPVC is cheapest; aluminium and timber cost more
• Glazing spec: double vs triple glazing, low-E glass
• Whether structural brickwork is needed (new bay installation)
• Planning permission fees (~£206 if an application is required)
Planning Permission: Bay Window vs Bow Window
Bow Windows
In most cases, replacing a flat window with a bow window does not require planning permission. Because the brickwork beneath stays flat, you’re not altering the building’s footprint — it typically falls under Permitted Development Rights.
No permission usually needed if: it’s a like-for-like replacement of a similar size and projection.
Bay Windows
Bay windows are more likely to need planning permission, because installing a new bay alters the building’s footprint (the brickwork must change shape). However, replacing an existing bay with one of the same size and projection usually falls under Permitted Development.
When Either Type Will Require Permission
• Your property is a listed building
• Your home is in a conservation area
• You’re in a flat or maisonette
• It’s a completely new projection where none existed before
Always check with your local planning authority before starting work. Enforcement notices and removal orders are a real risk if you proceed without the correct approvals.
Does a Bay Window Need a Foundation?
• Full-height bay windows: Yes — the angled brickwork carries load and typically requires a proper foundation at ground level.
• Cantilevered bay windows: Not always — upper-floor bays can be supported by steel brackets without a ground foundation.
• Bow windows: No — the flat brickwork below distributes load in the conventional way.
Frequently Asked Questions
What is the main difference between a bay and a bow window?
Bay windows have 3 angled panels at 30–45°, creating a hard-edged angular projection. They have 4–6 panels at ~10° each, forming a smooth curve. Bay windows also require the brickwork beneath to follow the window shape; bow windows sit above flat brickwork.
Are bow windows more expensive than bay windows?
Yes typically 1.5 to 2.5 times more. Bow windows use more glass panels, require custom curved frames, and can involve more complex installation. Bay windows are the more budget-friendly choice.
Which lets in more light?
Bow windows. More panels mean more total glass area, which translates directly into a brighter room and wider views. If light is your priority, choose a bow.
Do bay windows add value to a house?
Yes. Bay-fronted properties consistently attract stronger buyer interest and higher valuations. The combination of extra floor space, character, and the iconic window-seat alcove makes them a genuine selling point.
How long do bay and bow windows last?
A well-installed uPVC bay or bow window typically lasts 20–25 years. Timber and aluminium frames can last 30–40 years with proper maintenance. Glazing units usually carry a 10-year manufacturer’s guarantee.
Can bay and bow windows be double-glazed?
Yes, modern bay and bow windows are double-glazed as standard. Triple glazing and low-E glass are available as upgrades for improved thermal performance and energy efficiency.
What does ‘bay fronted’ or ‘bow fronted’ mean?
These are property descriptions: a bay-fronted house has an angular projecting window forming the front elevation, while a bow-fronted house has a curved projection. Both are desirable period features that add curb appeal and property value.
