Are you planning the renovation of an old house and wondering what it really costs? Online calculators offer an initial guide, but the true cost factors often hide in the details. This guide shows you how to calculate renovation costs based on data and avoid expensive surprises.
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The topic briefly and concisely
Online calculators provide only a rough estimate; always plan for a buffer of at least 10% for unforeseen costs.
The costs for a complete renovation range from €400 to over €1,200 per square metre, heavily depending on the construction year and condition.
State subsidies (KfW, BAFA) can reduce costs by up to 70%, but they must be applied for before construction begins.
Renovating an old building is one of the biggest financial decisions property owners make. While numerous online calculators promise a quick cost estimate, a critical question often remains: How reliable are these figures really? In reality, standard calculators can hardly account for the individual building structure, regional price differences, and unforeseen deficiencies. The result is often budget overruns of 20% or more. This article provides you with an accurate, data-based roadmap. You will learn which cost factors are crucial, how to make optimal use of government subsidies, and why a data-driven analysis is the only way to a reliable cost estimate.
Understanding the Limits of Online Calculators
Online calculators are a useful first step to get a rough estimate of renovation costs. They are based on average values and cannot take into account the specific conditions of your property. A complete renovation is often priced between €400 and €1,000 per square metre, but this range is vast. For old buildings constructed before 1949, costs can even rise to over €1,200 per square metre due to complex building structures.
The biggest risk lies in undiscovered defects, such as damp in the basement or outdated wiring. Experts therefore advise to generally plan for a financial buffer of at least 10% of the estimated total costs for unforeseen expenses. An online tool cannot assess the condition of load-bearing parts or the presence of pollutants such as asbestos — factors that can quickly increase costs by five-figure amounts. These tools offer guidance, but not financial planning certainty.
Cost factors that calculators often overlook
A precise calculation must go beyond flat square metre prices and consider the individual trades. The official construction prices for residential buildings have risen by 3.2% from May 2024 to May 2025 alone, highlighting the necessity of current data. While a calculator gives a total amount, the actual costs consist of many individual items that vary greatly.
Here are typical costs that require detailed analysis:
Facade insulation: An external thermal insulation composite system (ETICS) costs between €100 and €200 per square metre.
Roof renovation: New insulation and covering quickly add up to €200 to €300 per square metre.
Window replacement: Modern triple-glazed windows cost around €500 each, excluding installation.
Heating system: Replacement starts at around €12,000, and for a sustainable heat pump, you should expect to pay between €30,000 and €50,000.
Electricity: A complete renewal of the electrical installation costs between €85 and €130 per square metre.
These figures demonstrate how inaccurate a general estimate must be. Therefore, a detailed analysis of core renovation costs is essential. Only then can a realistic budget be established, which also takes regional tradesmen's prices into account.
Energy Renovation: Carefully Weighing Costs and Benefits
The energetic renovation is the biggest lever for increasing value and reducing costs during ongoing operation. A comprehensive modernization can reduce the energy demand of an old building by up to 80%. This not only protects the environment but also your wallet, as the payback periods for many measures, due to high energy prices, are often only between 8 and 15 years.
A new heating system alone is often not the most efficient solution. The most effective strategy is to optimize the building envelope before renewing the plant technology. Facade insulation can reduce heating costs by about 13%, a new heating system by 25%. Combining both measures amplifies the savings. If you are planning the costs for your inherited house, the energy quality is the decisive factor for future value. Investing in insulation and modern windows is the foundation for lower operating costs and high living comfort.
Maximise savings potential through government subsidies
The government supports energy-efficient renovations with substantial grants and loans, significantly reducing the financial burden. The Federal Funding for Efficient Buildings (BEG) is the central tool here. Most important rule: The application must always be submitted before the construction work begins. Retrospective funding is excluded.
An overview of the most important funding programmes:
KfW Loan 261: For complete refurbishment to an efficiency house, there is a loan of up to €150,000 with a repayment grant of up to 60%, but no more than €90,000.
BAFA Grant (BEG EM): For individual measures like windows, insulation, or ventilation systems, you receive a grant of 15% on eligible costs up to €60,000. With an Individual Renovation Roadmap (iSFP), the grant increases to 20%.
Heating Replacement: Replacing an old fossil fuel heating system with a system based on renewable energies is funded with up to 70% of the costs.
KfW Supplementary Loan 358/359: Those who use a BAFA grant for individual measures can also apply for a subsidised loan of up to €120,000.
Finding the right funding is crucial to understanding the need for renovation. An early assessment, as made possible by an Online Check for Inherited Properties, helps with strategic planning.
The 5 Most Common Cost Traps in Renovating Old Buildings
Renovating old houses presents typical financial pitfalls that can blow any budget. Forward-looking planning based on reliable data minimises these risks. Pay special attention to the following five points to avoid overspending.
Ignoring hidden defects: Moisture, dry rot or asbestos contamination are often overlooked during a superficial inspection. A structural survey by an expert before purchase or planning is an investment that pays huge dividends.
Underestimating regional price differences: The costs for tradespeople can vary by up to 30% depending on the state and workload. Always obtain at least three comparable quotes from local businesses.
Changes to plans during construction: Any change made after construction has begun results in disproportionately high costs. Detailed execution planning before the first spade hits the ground prevents expensive corrections.
Overestimating DIY capability: Many homeowners plan to save costs through DIY work. Often, the time required and necessary expertise are underestimated, leading to delays and construction defects whose remediation costs more than the original savings.
Applying for funding incorrectly or too late: Bureaucracy has its pitfalls. Incorrectly filled applications or commissioning work before approval inevitably lead to funding being denied.
A realistic assessment of the renovation costs for an inherited house protects against unpleasant surprises.
From Estimation to Precise Analysis: The Data-Driven Path
You see: The question of how to calculate renovation costs for an old house online has two answers. The quick estimate via an anonymous calculator and the well-founded, data-supported analysis. For a decision of such magnitude, particularly in the context of an inheritance or sale, only the second answer provides a reliable foundation. This is precisely where Auctoa comes in.
Instead of relying on general averages, we access one of Germany's largest real estate databases. Our AI-supported analysis not only evaluates the current market value but also identifies the specific renovation potential of your property. The Auctoa Renovation Potential Report provides you with an objective, comprehensible calculation of the incurred costs and the expected increase in value. For heirs and owners, this means: no vague estimates, but a clear, data-driven decision-making basis. You'll know exactly which measures are worthwhile and can negotiate with banks and buyers on equal footing. Do you have any initial questions? Test our ImmoGPT and receive an immediate initial assessment.
sanierungskosten-fur-altes-haus-online-berechnen
Calculating the renovation costs for an old house online is a complex task that goes far beyond the use of simple calculators. While these tools provide an initial indication, a thorough analysis is essential for a sustainable financial plan. Taking into account the individual building structure, the current construction cost increases of over 3% per year, and the strategic use of subsidies are crucial for success. Ultimately, precise data and an expert-based assessment replace the risk of blanket estimates and provide the necessary security for your investment.
Additional useful links
Statistisches Bundesamt provides detailed information on construction prices and real estate price indices in Germany.
KfW provides information on funding programmes for energy-efficient refurbishment of existing properties.
Bundeswirtschaftsministerium offers a comprehensive dossier on the energy transition in the building sector.
Deutsche Energie-Agentur (dena) offers information and guides on the renovation of buildings and local spaces.
Verbraucherzentrale provides a guide to future-proof refurbishment of old houses.
Bundesverband Baustoffe – Steine und Erden e.V. provides information on current topics and developments in the construction industry.
BFW Bundesverband Freier Immobilien- und Wohnungsunternehmen e.V. provides information on market activities in the building and housing sector.
Initiative "Für Bauen im Bestand" provides information and advice on building in existing structures.
FAQ
How long does a complete home renovation take?
A complete renovation of a detached house typically takes between three and twelve months. The exact duration depends on the scope of the work, the coordination of the trades, and unforeseen discoveries in the building structure.
What role does the year of construction play in the renovation costs?
The year of construction is a crucial indicator. Houses from the 1950s to 1970s often have poor insulation and outdated technology. In pre-war buildings, problems with structural stability or listed elements can additionally increase costs.
What is an individual renovation timetable (iSFP)?
An iSFP is a document created by a certified energy consultant. It presents the current energy condition of your property and lists sensible renovation measures in a logical order. With an iSFP, you receive an additional funding bonus of 5% from BAFA.
Can I combine funding?
Yes, a combination is often possible and sensible. For example, you can combine a BAFA grant for window replacement with a KfW supplementary loan. However, double funding of the same measure (e.g. grant and tax bonus) is excluded.
What is the difference between restoration, renovation, and modernisation?
A refurbishment remedies defects and restores the building fabric (e.g., waterproofing a basement). Renovation is a cosmetic improvement (e.g., painting). Modernisation enhances the standard and energy efficiency (e.g., installing a heat pump). In practice, these measures often overlap.
How do I find reliable tradespeople for the renovation?
Recommendations from architects or energy consultants are a good source. Always obtain at least three detailed quotes and check references. Look for certifications and memberships in trade chambers or professional associations.
