Aluminium Window Cost Calculator (per m² and total)

How the calculation works

Aluminium window costs: what sets the price

Aluminium windows are one of the building elements where the price per square metre hides several different products. Two windows of identical size can differ widely in cost because of the frame, the glazing and the installation method. This calculator reduces the choice to a single estimate, which is useful for planning, but the estimate is only as good as the specification behind it. Understanding the three main drivers before requesting quotes avoids most of the surprises that appear once the work starts.

The frame: with or without a thermal break

The frame is the aluminium profile that holds the glass and fixes the window to the wall. Aluminium conducts heat very well, so the design of the profile matters as much as the material itself. A standard profile without a thermal break is a single extruded section. It is usually the cheaper option, but heat passes easily between the inside and outside faces. In cold weather the inner surface of the frame can drop below the dew point, producing visible condensation, which can lead to damp reveals and mould in room corners if it persists.

A thermal break profile has an insulating polyamide barrier between the outer and inner aluminium sections, which interrupts that heat path. It costs more, and the difference between quotes can be noticeable, but it is the usual choice for replacement work in Britain today. Whether it is essential depends on the building, the exposure of the site and the requirements that apply to the work, so check with building control rather than assuming either way.

The glazing: single, double and low-e

Single glazing is one pane of glass, typically 4 or 6 mm thick. Its U-value, the rate at which heat passes through the glass, is much higher than that of any double-glazed unit. It is still found in unheated conservatories, outbuildings and storage spaces, but it is rarely appropriate for a habitable room where thermal comfort is expected.

Double glazing uses two panes separated by a sealed cavity filled with air or argon. Its U-value is considerably lower than that of single glazing, and the exact figure depends on the spacer and the gas fill. It is now the usual minimum for new work and replacement windows. The U-value of a glazing unit is determined under BS EN 673, and any quote should state the glass make-up, for example 4/16 argon/4 low-e, so that the figure can be checked against the manufacturer's declared data.

Low-e (low emissivity) double glazing adds a thin metallic coating that reflects heat back into the room in winter and limits solar heat gain in summer, depending on the coating and the orientation of the window. Its U-value is lower again than that of standard double glazing. The energy difference over a year depends on the climate, the orientation of the room and how the heating is used, so the saving should be estimated for each home rather than taken as a fixed figure. A flat in Manchester with north-facing windows will see a different benefit from a south-facing conservatory in Bristol.

Market tiers

Not all aluminium windows sit in the same price band. The table gives a rough guide to how the main options are usually positioned in the UK market. The tiers are qualitative, because the actual cost depends on the profile system, the fabricator and the region.

Installation is usually charged per window on a standard job. Large units, difficult access, upper-floor work and the removal of heavy or stone-set existing frames can increase labour significantly, so the installation field should reflect the real site rather than a typical one.

How the calculator works

The formula is C = N × (L × H) × Pm + N × Pi. Each term has a clear role. N is the number of windows. L and H are the average width and height of each window in metres, so L × H gives the area of one window in square metres. Multiplying by N gives the total glazed area, and Pm converts that area into a material and fabrication cost. Pi is the installation cost per window, and it is added only when installation is included. Because it is multiplied by N and not by area, installation does not change with the size of the windows.

Two consequences follow from this structure. First, doubling the number of windows doubles both parts of the total. Second, a window that is larger in area costs more in the material part but not proportionally more in installation, because installation is charged per window. For example, six windows of 1.2 m by 1.5 m give 10.8 m² of glazed area. Nine windows of the same size give 16.2 m². The area rises by half, and the installation part also rises by half, because it is counted per window. Where the windows are of very different sizes, calculate each group separately and add the totals.

Edge cases and limits

The calculator assumes rectangular windows of a single average size. Bay windows, arched heads, circular units and irregular shapes should be measured as their bounding rectangles or split into separate groups. The calculator does not model the opening type, so sliding, casement and tilt-and-turn windows are not priced differently. Opening type, hardware, locks and security glazing can change the price substantially, so treat the result as a starting point for those options.

Doors, roof lights and curtain walling fall outside the scope of this estimate. The calculator also does not include scaffolding, making good plaster, or decorating after installation, unless those costs are added separately.

When not to rely on this estimate

Do not treat the result as a fixed price for a listed building, a property in a conservation area, or any project where the window design is controlled by a planning condition. Those projects may require planning permission or listed building consent, and the specification may be restricted to particular profiles, materials or sightlines. In these cases the specification comes first and the cost follows.

Common mistakes when ordering

Measuring the old frame instead of the opening. The dimension to give the fabricator is the size of the masonry opening, measured wall to wall, with a small allowance for the fixing and the sealing foam. Using the size of an old frame as the reference is risky, because old frames may have been fitted with irregular gaps or poor reveals, and a window made to their size may not suit a sound opening.

Comparing quotes without the specification. Two quotes with the same price per square metre may refer to profile series of different depth and quality, to glazing with different U-values, or to frames with different air and water tightness ratings. Ask each fabricator for the same information so that the comparison is like for like.

Forgetting what is included. Ironmongery, hinges, cills, perimeter sealant and compression seals are often included in quotes from established fabricators, but not in every case. Confirm the full list before signing anything.

What to ask for in a written quote

A written quote that can be compared with others should state:

• the profile reference and series
• the glazing make-up, for example 4/16 argon/4 low-e
• the air permeability class to BS EN 12207
• the water tightness class to BS EN 12208
• the wind resistance class to BS EN 12210, where relevant
• whether the cill, ironmongery, sealant and installation are included
• the warranty period and what it covers

Standards and testing

Window performance is established by laboratory testing. The wind resistance, air and water tightness and thermal performance of windows and external doors are assessed to BS EN 14351-1 by accredited testing laboratories, and the manufacturer's declaration of performance is based on those results. Ask the fabricator for the declaration of performance and the test evidence behind it. In England, the energy requirements for replacement windows are set out in Part L (Conservation of fuel and power) of the Building Regulations, with guidance in Approved Document L. Wales has its own version of Part L, and Scotland applies the Building Standards.

Using the result

The calculator gives a planning figure. Use it to judge whether the budget is realistic, to compare the effect of glazing and frame choices, and to prepare the questions for the fabricator. Before committing, get at least two or three written quotes from local fabricators with verifiable references from similar jobs, and ask building control or the competent person responsible to confirm that the chosen windows meet the requirements for the property.