At the latest when an uncomfortable draught is seeping through the cracks on chilly days, it is time for a window renovation. However, window renovation in old buildings is often worthwhile at a much earlier stage. After all, even the best facade or roof insulation is of little use if the heat escapes through windows that are no longer fit for purpose. Moreover, modern windows do not only offer better insulation, but also better burglary protection. Even in old buildings, it is not always necessary to completely replace all windows during renovation. Because worn seals or inadequate glazing can be replaced and that alone can work small miracles. But especially when it comes to older wooden windows, it is worth considering whether a repair is actually worthwhile or whether, in the long term, the initially high-priced window replacement would be the better investment.
When renovating old buildings to make them energy-efficient, one of the individual measures to be taken is window renovation. Much of the heating energy in old buildings dissipates through the windows. This is why window renovation should be one of the first measures to reduce energy consumption. Minor repairs may be sufficient depending on the condition, year of construction and type of windows. If the windows in the old building still have single glazing, simply replacing the sealing strips will not produce any major benefits. This is because the energy dissipation from a window with single glazing is up to five times higher than from a window with double glazing. Triple glazing further improves these values. Window manufacturers specify the heat transfer coefficient as the U-value. In general, the lower the U-value, the lower the energy loss through the window. While single glazing barely achieves a U-value of around 5 W/(m²K) and box-type windows halve this value at best, double glazing has a low heat transfer coefficient of just over 1.1 W/(m²K). Triple glazing is still significantly lower. For comparison, here is a small overview of window types currently still in use in old buildings with their average U-values in W/(m²K), which can vary depending on the year of construction:
single-glazed windows made of wood, plastic, metal: 4.5 to 6.1
composite windows made of wood or plastic: 2.4 to 2.6
metal composite windows from 1978: 4.0
wooden or plastic box-type windows: 2.3 to 2.6
insulated glass windows made of metal: 3.1 to 4.1
insulated glass windows made of plastic or wood: 2.6 to 2.8
insulated glass windows with LOW-E coating, frames made of plastic, wood with metal trim or aluminium: 1.5 to 1.6
If the window frames are still in good or very good condition, there is no need for new windows. A window renovation can also comprise restoration, simple repair work or the replacement of individual parts. In any case, it is advisable to consult an experienced window fitter about the options for improving the window density before replacing the windows.
A restoration of old windows can be considered if the window frames are in good condition. If the windows have well-preserved plastic frames, for example, and only the sealing strips are brittle, these can be replaced at low cost. If well-maintained wooden windows do not yet have any seals, the window fitter can retrofit these himself subsequently by means of milling. Depending on the condition of the existing window, both measures can go a long way.
Listed buildings without double glazing are an example of when it makes sense and is sometimes the only alternative to replace only the glazing and not the complete windows. If the window frames are strong enough, an additional pane can insulate a single-glazed window both energetically and acoustically. On average, the U-value can be improved by up to 40 percent.
Alternatively, the window renovation can be carried out by replacing the glazing, always provided that the window frame still complies with the specifications according to the Energy Saving Ordinance. With this type of window renovation, burglary protection can also be improved by using laminated glass or locks on the window handles.
If the window frames are getting on in years and are neither visually appealing nor load-bearing enough for additional glazing, replacing the windows is usually the only option. If you are also looking for a long-term solution when renovating your windows and would like to receive state subsidies, it is better to completely replace the windows. This costs more than a repair at the time, but saves many years or even decades of further window renovation. In addition, new windows increase the value of a property considerably when it is sold at a later date and, as an improving renovation measure, also allow for rent increases. In both owner-occupied and rental properties, new windows also ensure a pleasant living ambience. Subsidised or financed with favourable loans, window replacement pays off in most cases due to the associated energy savings.
Modern windows also provide more security. Plastic windows, for example, have a tenon locking system (that varies depending on the manufacturer), which makes it much more difficult to pry open than simple wooden frame windows. A modern window with triple glazing is a much greater obstacle for potential burglars in old buildings than a wooden window with single glazing that is in need of renovation. Triple glazing or double glazing with inert gas in the space between the panes keeps out the heat or cold, depending on the season, as well as irritating noise. This is due to the total energy transmittance, known as the g-value in short. At the same time, the low heat transfer coefficient ensures that the heat from the heating system or cool air in the room in summer remains in the living spaces. Also not to be underestimated when it comes to insulation is the advantage of a new window frame. Many apartments in old buildings are located on busy streets or in city centres. New multi-paned windows achieve a remarkable level of noise insulation, which can be between 25 and 50 decibels, depending on the sound insulation class. Here are the advantages of window renovation through window replacement at a glance:
reduction of heating costs
improvement of the indoor climate
reduction of the noise level from the outside
increase in the value of the property
longer renovation intervals
environmental protection through lower carbon emissions
better burglary protection
eligibility for state subsidies
To ensure that the windows fit properly afterwards, you need moderate temperatures, as building materials react differently at sub-zero temperatures. Moreover, it is much more pleasant for the occupants of the property when it is warmer outside. Because depending on the size and type of window, the replacement can take a few hours. Another prerequisite is dry weather, so that it does not rain into the property when the windows are replaced. Summer is therefore ideal and spring and a golden autumn are definitely better than winter for replacing windows.
If the replacement of old windows is associated with significant energy savings and is important in terms of the energy transition, subsidies are available for individual measures within the framework of the Federal Funding for Efficient Buildings (BEG). In order to be eligible for a subsidy, the application must always be submitted to KfW before the start of the window renovation and now also before the conclusion of the contract. For the property to actually be considered an old building eligible for funding, a building application from before 1995 is required. A KfW loan or the BAFA grant cannot be used concurrently or together as a tax deduction. But property owners can choose which subsidy is most suitable for them. In addition, many federal states have their own subsidy programmes.
KfW development loan
Homeowners have the opportunity to apply for low-interest development loans with a repayment subsidy from KfW. Depending on whether it is an annuity loan or a bullet loan and how long the term is, the interest rate is currently between 1.27 and 1.48 percent. For window renovation, KfW grants a repayment subsidy of 20 percent if the required energy values are achieved, so that with a maximum loan of 60,000 euros, only 48,000 euros plus interest would have to be repaid.
BAFA investment subsidy
If you do not need a loan, you can apply for BAFA investment subsidies. They also amount to 20 percent of the investment volume, which is applied for window replacement from 2,000 euros and up to a maximum of 60,000 euros per residential unit.
Without having to apply in advance, property owners can alternatively take advantage of the tax incentive for energy-efficient building renovation. A window renovation involving the replacement of windows are tax-deductible as an individual measure at up to 20 percent of the cost, up to a maximum of 40,000 euros. The tax reduction is spread evenly over three years. Property owners can even deduct 50 percent of the costs of specialist planning or construction support for an energetic renovation from their income tax return.