Draughts along the sofa, condensation on the glass every morning, the tram rattling through the living room: in many homes in Geneva and Vaud, the windows are the weak point of the building envelope. A window from the 1970s or 1980s loses three to five times more heat than a current triple-glazed model. Replacing it is one of the most visible jobs in a renovation, and one where mistakes are expensive, because a window stays in place for thirty years. This guide explains how to choose, what the rules say in Geneva and the canton of Vaud, which subsidies exist in 2026 and what to budget.

When should windows be replaced

An old window does not always need replacing. A sound, well-maintained timber frame that is simply out of adjustment can often be kept: the seals are renewed, the glazing is swapped or the hardware is adjusted. Full replacement makes sense in the following situations.

  • The glazing is single or early double glazing without a low-emissivity coating. You can tell by the cold-wall feeling when you bring your hand close in winter.
  • The frame is damaged: rotten timber at the bottom, aluminium without a thermal break, yellowed and warped PVC that no longer closes properly.
  • Condensation forms between the two panes: the seal of the insulating unit has failed and the insulating gas has escaped.
  • Outside noise is a nuisance, especially along main roads, tram lines or under the airport flight paths.
  • You are renovating the façade or replacing the heating: it is the right moment to deal with the envelope in one go.

Understanding U-values

A window's thermal performance is measured by its heat transfer coefficient, in watts per square metre per kelvin. The lower the value, the better the window insulates. Two values appear on quotes and they must not be confused.

  • Ug refers to the glazing alone. Standard triple glazing reaches 0.5 to 0.7 W/m²K, modern double glazing about 1.1.
  • Uw refers to the complete window, frame included. This is the one that matters. The frame insulates less well than the glass, and a metal spacer between the panes creates a thermal bridge all the way round.

For a replacement window in an existing building, cantonal requirements based on the MoPEC and the SIA 380/1 standard in practice call for a Uw of about 1.0 W/m²K at most. Triple glazing has become the norm in French-speaking Switzerland; double glazing is now only justified in special cases, such as a heritage window with very slim profiles. Ask for a so-called warm-edge spacer made of synthetic material rather than aluminium.

One last useful figure is the solar factor, g. It shows the share of solar energy that passes through the glazing. On a south façade, a high g brings free heat in winter; on the west and under a roof, think instead about solar shading to avoid overheating in summer.

Timber, PVC, timber-aluminium or aluminium

The choice of material depends on budget, how much maintenance you accept and the look of the façade.

  • PVC is the most affordable and needs almost no maintenance. Its profiles are wider, which slightly reduces the glazed area, and it is sometimes refused in protected areas.
  • Timber gives a fine finish and a good environmental footprint, but needs a stain or paint on the outside every five to ten years depending on exposure.
  • Timber-aluminium combines warm timber inside with an aluminium cladding outside that protects it from the weather. It is the most common choice in Switzerland for a long-lasting project, and it receives a higher subsidy in the canton of Vaud.
  • Thermally broken aluminium allows slim profiles and large glazed openings. It is more expensive and has a high embodied energy.

Whatever the material, check the quality of the hardware, the burglar-resistance class if the home is on the ground floor, and an integrated trickle vent if the room has no mechanical ventilation.

Installation is half the performance

An excellent window badly installed lets air and water through the joint with the masonry. In a renovation there are two methods.

  1. Retrofit installation: the old outer frame is kept and the new frame is fixed over it. The job is quick and leaves the reveals untouched, but you lose a few centimetres of glass on each side.
  2. Full removal: the old frame is taken out completely and the new window is set into the masonry. The glazed area is maximised and the joint can be redone properly, at the cost of making good the plaster and paint around the opening.

In both cases, ask for a sealed installation in line with industry guidelines: an airtight tape on the inside, a vapour-permeable tape on the outside and insulation in the joint between them. Polyurethane foam alone is not enough. Also plan for the external sill and the blind boxes, which are often very poorly insulated in older buildings.

Noise: the window as acoustic protection

A window's sound insulation is measured by its sound reduction index, in decibels. Standard triple glazing reaches about 32 to 35 dB. Along a noisy road, asymmetric acoustic glazing, with panes of different thickness or laminated glass, can exceed 40 dB. Every 10 dB gained roughly halves the perceived noise.

Around Geneva airport, Genève Aéroport has funded since the 2000s a soundproofing programme for noise-sensitive rooms in buildings exposed to alarm values. If your home is in one of the neighbouring communes, ask before ordering your windows: the work it covers follows a precise specification.

Permits: what differs between Geneva and Vaud

Replacing windows like for like is generally treated as maintenance. As soon as the appearance of the façade changes, the situation is different.

  • In Geneva, a change of material, colour, glazing bars or opening type in principle requires a building permit under the fast-track procedure, the APA. In protected zones such as the Old Town, and for listed or inventoried buildings, the opinion of the monuments, nature and sites commission is required and the choice of profiles can be tightly controlled.
  • In the canton of Vaud, the planning and building act, the LATC, makes works that alter the external appearance subject to municipal approval. Minor works can be exempted from public inquiry, but the municipality decides. In Lausanne's historic areas, contact the planning department before ordering.

In an apartment building, windows are part of the façade. In a condominium (PPE), they are usually common parts or at least governed by the building regulations: replacing them in a single unit, especially if the appearance changes, requires a decision of the owners' meeting. In a rental, it is up to the landlord to decide and pay; a tenant does not replace their own windows.

Subsidies in 2026

The Buildings Programme is run by each canton, and windows are not treated the same way everywhere.

  • In the canton of Vaud, window replacement in a building constructed before 2000 is subsidised in 2026 at 80 francs per square metre of masonry opening, with glazing at Ug 0.7 W/m²K at most. A bonus of 50 francs per square metre is added for timber or timber-aluminium frames. The subsidy is capped at 4,000 francs, 5,000 francs with the bonus, and at 20 % of the cost of the works. A CECB Plus is required.
  • In Geneva, the GEnergie programme, run by the cantonal energy office and SIG, subsidises envelope renovation according to a schedule revised every year. The conditions for replacing windows alone are not the same as for a full renovation: check the current schedule on ge.ch before signing.

In both cantons the golden rule is the same: the application must be submitted and approved before work starts. A window ordered too early can no longer be subsidised. Maintenance and energy-saving costs are also largely tax-deductible for owners.

After the replacement: ventilate more

New windows are almost perfectly airtight. The old ones let air in through their worn seals, which provided unintentional ventilation. Without that air change, the moisture produced by cooking, showers and breathing stays inside, and mould can appear in cold corners, behind furniture or around the new windows.

There are three answers. Air the rooms fully two to four times a day for five to ten minutes, rather than leaving a window tilted all day. Choose windows with vents built into the frame. Or, as part of a wider renovation, install single or balanced mechanical ventilation, which renews the air without losing the heat. A hygrometer costing a few francs helps keep indoor humidity between 40 and 60 %.

How much does window replacement cost

Prices vary with size, material, acoustic glazing and site access. The following ranges, installation included and excluding VAT, are for a standard two-casement window of about 1.2 by 1.4 metres in Geneva or the canton of Vaud:

  • PVC window, triple glazing: about 1,200 to 1,900 francs.
  • Timber window, triple glazing: about 1,500 to 2,400 francs.
  • Timber-aluminium window, triple glazing: about 1,800 to 2,800 francs.
  • Thermally broken aluminium window: about 2,200 to 3,500 francs.
  • Extra for enhanced acoustic glazing: about 150 to 400 francs per window.

On top of this may come removal and disposal of the old windows, making good the reveals, replacing blinds or shutters and, in an apartment building, scaffolding or a lift platform. For a four-room apartment with eight to ten windows, a budget of 15,000 to 25,000 francs is a realistic order of magnitude. Allow six to ten weeks for manufacturing; installation itself often takes less than a day per window.

Common mistakes

  • Comparing quotes on the Ug of the glazing instead of the Uw of the complete window.
  • Ordering before receiving the subsidy approval or the building permit.
  • Neglecting installation: a foam joint without sealing tapes cancels part of the gain.
  • Forgetting the blind boxes, which remain a hole in the insulation.
  • Changing nothing in your ventilation habits and finding mould in the first winter.

Frequently asked questions

Is triple glazing mandatory in Switzerland?

It is not required as such, but the Uw of about 1.0 W/m²K demanded for a replacement window is hard to reach otherwise. It is also needed for the Vaud subsidy, which sets glazing at Ug 0.7 at most.

Do I need a permit to replace windows in Geneva?

Not for a strictly like-for-like replacement. A change of material, colour or glazing bars in principle requires an APA, plus the monuments commission's opinion in a protected zone or for an inventoried building.

Can windows be replaced in winter?

Yes. Each window is removed and replaced the same day, so the room is open for only a few hours. Winter jobs often come with shorter lead times.

How much energy does new glazing save?

In a home with windows from the 1970s or 1980s, replacement often cuts heating demand by 10 to 20 %, more if the old frames were very leaky. The gain in comfort, with no cold wall and no draughts, is immediate.