Ordering windows without an installation package can give you more control over your project, your installer and your budget. But knowing how to order supply only windows properly matters: aluminium windows are made to your sizes and specification, so a small mistake in a survey dimension, opening detail or glazing choice can be expensive to put right.
For homeowners, self-builders and trade customers, the best supply-only order starts well before a quotation. It starts with a confirmed opening, a clear idea of how each window should operate, and a specification that suits the building rather than simply the lowest initial price.
Start with the finished opening, not the old frame
The most common ordering error is measuring the window that is being removed rather than the structural opening the replacement will sit within. Existing timber or uPVC frames can conceal uneven brickwork, old packers and inconsistent reveals. Measure the opening after the old frame has been removed where possible, or allow for a site survey by an experienced installer before production begins.
Take the width at the top, middle and bottom of the opening, then take the height at both sides and in the centre. Record the smallest dimensions, and check whether the aperture is square by measuring diagonals. If there is a meaningful difference between those diagonal measurements, the opening may need correction or the installation detail needs to account for it.
Your ordered frame size must include an appropriate fitting tolerance. The exact deduction depends on the system, substrate, fixing method and whether insulated cavity closers, render, cladding or internal finishes are involved. Do not assume a standard deduction will suit every project. A tight masonry opening and a new timber-frame extension demand different consideration.
Confirm the building line and cill detail
Decide where the frame will sit in the wall build-up. On a cavity wall, this may be towards the outer leaf, centred within the cavity or positioned to align with insulation. On a new extension, the location should work with insulation continuity and external finishes. This decision affects frame depth, cill projection, flashing details and the appearance of the reveal.
Specify whether you need a cill, and how far it should project beyond the finished external face. A cill that is too short can leave the façade looking unfinished and may direct rainwater back towards the wall. Also establish whether trickle vents are required and where they will sit, as these add to the overall frame height.
How to order supply only windows by room and function
A window schedule is far more reliable than a collection of measurements in an email. Give every window a reference, such as W01, W02 and W03, and identify the room it serves. Include the overall frame width and height, opening style, handing, colour, glazing specification, cill requirement and any special notes.
For opening casements, handing must be described from the outside looking in. A side-hung sash hinged on the left when viewed externally opens differently from one described from inside the room. For top-hung windows, confirm whether the sash is for ventilation only, an emergency escape route or both.
Bedrooms may require a compliant means of escape where the window serves a habitable room and there is no alternative protected escape route. Ground-floor windows, bathrooms and hard-to-reach locations may benefit from restricted openings. Kitchens often need practical ventilation, while a large fixed picture window can be the best choice where light and uninterrupted views matter more than opening function.
A supply-only order should also state whether the window is to be internally or externally beaded. Premium aluminium systems are generally designed with security and weather performance in mind, but the correct configuration still depends on the application. If you are matching new windows to sliding or bifold doors, include sightline preferences and finish requirements early rather than treating them as an afterthought.
Choose an aluminium system for performance as well as appearance
Not every aluminium window profile is intended for the same type of project. A well-specified system gives you slim, durable frames, but it must also meet the thermal, security and weathering requirements of the property.
Smarts Alitherm 400 Windows are a versatile option for contemporary replacement and extension projects, with thermally broken aluminium profiles and a broad choice of configurations. Cortizo Casement Windows suit projects where a refined, modern profile is a priority, while the Cortizo Hidden Sash Windows range creates a particularly clean elevation by reducing the visible distinction between fixed and opening sections. For more demanding architectural specifications, Schuco AWS80SC Casement Windows can provide a premium solution with strong performance and design flexibility.
Compare frame depth, visible sightlines, maximum sash sizes and available opening types alongside the headline U-value. A very slim-looking system may have limits on sash dimensions or glass thickness. Conversely, a deeper system may be the sensible choice for a highly exposed elevation or a large opening that needs greater structural capacity.
Colour is equally worth confirming at order stage. Anthracite grey remains popular, but aluminium can be specified in a wide selection of powder-coated finishes, including dual colours for a darker external façade and a lighter internal finish. Ask whether the chosen finish is stock or a special-order colour, as this can affect lead times.
Specify glazing before approving the quotation
The glazing unit does much of the work in an energy-efficient window. Thermally broken aluminium profiles combined with high-performance double or triple glazing can deliver strong insulation without sacrificing the slim-frame appearance that makes aluminium so popular.
For each elevation, consider the balance between heat loss, solar gain, glare, privacy and safety. A south- or west-facing glazed extension may benefit from solar-control glass to reduce overheating, especially where the windows sit alongside large sliding doors or roof glazing. On a cold north-facing wall, a low-emissivity unit with warm-edge spacer technology may be the greater priority.
Safety glass is required in certain critical locations, including low-level glazing and areas close to doors, but the exact requirement depends on the design and location. Obscure glazing may be necessary for overlooking, and acoustic glass can be worthwhile near busy roads. These are not upgrades to guess at from a product photo. Provide the elevation and the purpose of the room so the specification can be checked properly.
Triple glazing can improve thermal performance, although it adds weight and can affect maximum sash sizes, costs and lead times. It is often a strong choice for a well-insulated new build, but double glazing may be the more proportionate solution for some renovations. The right answer depends on the wider fabric of the building, not one number on a quote.
Check compliance, lead times and delivery access
Supply-only windows still need to satisfy the relevant Building Regulations for the project. This can cover thermal performance, ventilation, means of escape, safety glazing and replacement-window requirements. Your installer or building control body should confirm the final installation approach, particularly for structural alterations, new openings and extensions.
Before placing the order, ask for a final production drawing or order acknowledgement showing every size, opening direction, colour, glass specification, cill and accessory. Read it line by line. Check the external view of each window, not only the internal elevation, and confirm that the dimensions are frame sizes rather than brickwork opening sizes.
Delivery needs planning too. Aluminium windows are protected for transport, but large glazed units are heavy and need safe handling on site. Tell the supplier about narrow roads, restricted access, stairs, a lack of off-loading equipment or a required delivery date coordinated with scaffolding and installation labour. A delivery arriving before the building is secure can create avoidable storage and damage risks.
Make the order easy for your installer to fit
A reliable installer will want the window schedule, approved drawings, installation position and glazing details before arriving on site. They also need to know whether they are responsible for removing existing frames, making good internal plaster, fitting trims, sealing externally and disposing of waste. Supply-only means the product procurement is separate, not that these responsibilities disappear.
At Bifolding Door Factory, supply-only customers can configure premium aluminium systems with the same attention to thermal efficiency, security, approved components and finish quality expected from an installation-led project. Clear specifications upfront help avoid late changes, protect lead times and give your installer the information needed to achieve a neat, weather-tight result.
A carefully checked supply-only window order gives you choice without unnecessary risk. Take the time to confirm the survey, glazing and installation detail before manufacturing starts, and your new windows can arrive ready to perform for years rather than becoming the next task on the renovation list.