Aluminium bay windows push a room outward, catch light from three directions and give you a deep sill to sit on or fill with plants. We supply them across South Africa, made to order in our workshop in Laser Park, Roodepoort: each face of the bay is one of our standard aluminium windows, joined to the next with an angled corner post to suit your bay. This guide explains the types, how the sizes work, what aluminium bay windows cost, and how to order.
Every window in a bay can be any of our standard windows: see our aluminium windows, especially top hung aluminium windows for the opening sides and fixed aluminium windows for the centre.
In this guide
What are aluminium bay windows?
A bay window is a group of windows that projects out from the wall of a house, usually with three faces: a wide centre light parallel to the wall and two side lights angled back to it. The builder forms the bay itself (the floor or sill, the walls under the windows and the roof or lintel above), and the windows fill the openings. Aluminium bay windows suit this well: the frames are slim, so more of the bay is glass, and they never need painting or swell in the rain.
Why aluminium for a bay window?
- Slim frames, more glass. Aluminium is strong for its size, so the frames and corner posts stay slim and the bay feels lighter and brighter than one in timber.
- No rot, no painting. A bay faces the weather on three sides. Powder-coated or anodised aluminium does not swell, rot or need repainting, which matters on the corners where timber bays usually fail first.
- Safety glass as standard. Every light is glazed with 6.38 mm laminated safety glass, important in a bay where the glass often comes down near the sill.
- Matches the rest of the house. The bay uses the same windows, colours and frames as the other windows, so the whole house looks like one design.
Types of aluminium bay windows
- Canted bay: the classic bay, with the side lights at 135° to the centre, so the bay is shaped like half an octagon in plan.
- Box bay: square corners at 90°, so the bay is a small rectangle in plan; common on modern homes and kitchens.
- Other angles and bow windows: bays with more lights or other angles, and curved bow windows made of several narrow lights, are quoted on request.
Choosing the windows for each face
Because every face is one of our standard windows, you can mix opening and fixed lights to suit the room.
- Top hung sides, fixed centre: the most popular layout. The side lights open for a cross-breeze and keep ventilating in light rain; the centre stays fixed for an unbroken view.
- All top hung: more fresh air in a kitchen or a hot west-facing room.
- Side hung sides: wider openings for airflow, easy to clean from inside.
- Obscure glass in the side lights where a bay faces a neighbour or the street.
Matching the sizes and heads of all three windows gives the bay a clean line, so choose the same height for every face. For seats, nooks and room-by-room inspiration, see our 12 bay window ideas.
Sizes: how wide and deep is a bay?
Work out the bay from the windows. For a canted bay at 135°, each side light projects about 0.71 of its width outward and adds about 0.71 of its width to the overall width. For a box bay, the side lights project their full width.
| Bay (three lights, 1 200 mm high) | Centre | Sides | Overall width | Projection |
|---|---|---|---|---|
| Canted, 135° | 1 200 mm | 2 × 600 mm | about 2 049 mm | about 424 mm |
| Canted, 135° | 1 500 mm | 2 × 900 mm | about 2 773 mm | about 636 mm |
| Box, 90° | 1 200 mm | 2 × 600 mm | about 1 200 mm | about 600 mm |
| Box, 90° | 1 800 mm | 2 × 600 mm | about 1 800 mm | about 600 mm |
These figures are for the windows only. The corner posts and the frame sizes, which are 10 mm smaller than the catalogue size each way, change the exact numbers slightly, and your builder sets the brickwork to suit. Send us the plan or the opening sizes and we confirm the final sizes before manufacture.
Aluminium bay windows cost
The cost of aluminium bay windows is the price of each window plus the angled corner posts, which we quote with your bay. Window prices are fixed and online:
For example, a canted bay with two 600 × 1 200 mm top hung side lights in the Casement 28 frame (R1 854 each) and a 1 200 × 1 200 mm fixed centre (R1 858) comes to R5 566 for the windows, excluding VAT. In the 30.5 mm Standard frame the side lights are R2 181 each, so the windows come to R6 220. The corner posts are added to the quote, and prices are the same in all five colours.
Double glazing is available on the 30.5 mm Standard frame and in the Casement 34 top hung frame if the bay faces a busy road or a cold wind; see double glazed windows. Laminated safety glass is standard in every light, which matters in a bay because the glass usually comes down close to the sill, and the rules on safety glass near floors are set in SANS 10400-N, published by the SABS.
Bay window ideas by room
- Lounge: a canted bay with a deep sill makes a window seat with a view on three sides. A fixed centre keeps the view clear; top hung sides bring in a breeze.
- Kitchen: a box bay over the sink gives a sunny sill for herbs and room to lean in to clean. A top hung vent above the tap stays reachable.
- Bedroom: a small canted bay makes a reading nook and lets in morning light from the side. Obscure glass in the side lights helps privacy.
- Dining room: a wide bay brings the garden to the table. Matching the bay to a patio door nearby keeps the elevation tidy.
Fly screens and burglar bars for bay windows
The opening lights of aluminium bay windows can take our roll-up fly screens and aluminium burglar bars, both made to the opener sizes of our windows. Fly screens roll away when you want the full view; burglar bars match the frame colour. The fixed centre light has no opener, so it needs neither. See aluminium fly screens and aluminium burglar bars for prices.
Aluminium bay windows in Gauteng
We make aluminium bay windows in our workshop in Laser Park, Roodepoort, so customers in Johannesburg, Pretoria, the East and West Rand and the Vaal can collect them free or have them delivered, with the delivery cost worked out by distance. See aluminium windows Gauteng for collection and delivery across the province. We deliver bays to the rest of South Africa too.
How to measure for a bay window
- Measure each face of the bay separately: the width of each opening at the top, middle and bottom, and the height at both sides.
- Measure or note the angle where each side meets the centre, usually 135° for a canted bay or 90° for a box bay.
- Note which lights must open and which way, and any obscure glass.
- Send the sizes with a simple sketch or the plan; we confirm the windows and the corner posts before anything is made.
If the bay is still being built, it is easiest to design it around our standard window sizes from the start; your builder then forms the openings to suit. Our guide to aluminium window sizes explains how windows are measured.
Common mistakes to avoid
- Measuring the bay as one opening. Each face is a separate window, so measure and order each one.
- Mixing window heights. Different heights break the line of the bay; keep the heads and sills level.
- Forgetting the opener direction. Top hung side lights open outward, so check that gutters, downpipes or plants outside will not get in the way.
- Leaving the roof to last. The bay roof or lintel carries the load above the windows, not the window frames. Your builder must finish it before the windows go in.
- No room to clean. A fixed centre light cannot be cleaned from inside on the outside face, so plan access, or choose an opening centre.
How to order aluminium bay windows
Send your bay sizes, angles and the windows you want to our team, by WhatsApp on 076 613 4418 or by email to sales@coetzglazing.co.za, and we send a fixed quote that includes the corner posts. You can also price the windows themselves in the online estimator first. Once the quote is accepted and paid, the bay is made to order in our workshop in 3 to 7 working days. It is delivered as separate windows with the corner posts, ready for your own builder or installer to join and fit on site; our windows are supply only.
Aluminium bay windows: frequently asked questions
What is an aluminium bay window?
A group of aluminium windows that projects out from the wall, usually a centre light with two angled side lights, joined by corner posts.
How much do aluminium bay windows cost?
The windows are priced online and the corner posts are quoted with your bay. A typical canted bay with two 600 × 1 200 mm top hung sides and a 1 200 × 1 200 mm fixed centre comes to R5 566 for the windows in the Casement 28 frame, excluding VAT, plus the corner posts.
Do you make box bay windows as well as angled bays?
Yes. We supply canted bays with 135° corners and box bays with 90° corners. Other angles and bow windows are quoted on request.
Can the side windows of a bay open?
Yes. Each face is a standard window, so the side lights can be top hung or side hung and the centre fixed or opening.
Can aluminium bay windows be double glazed?
Yes, using windows in the 30.5 mm Standard frame or top hung windows in the Casement 34 frame.
How long do aluminium bay windows take?
Aluminium bay windows are made to order in 3 to 7 working days once your quote is accepted and paid, then collected from Laser Park or delivered.
Is a bay window delivered assembled?
No. It is delivered as separate windows with the angled corner posts, which is easier to carry and set into the opening. Your installer joins them on site.
Do you install aluminium bay windows?
No. Our windows are supply only. The bay is delivered as separate windows with the corner posts; your builder forms the bay and your installer joins and fits the windows on site.
Coetz™, Unit 2, 84 Ridge Road, Laser Park, Johannesburg. Call 010 412 0062, WhatsApp 076 613 4418 or use our contact page.