Property Valuation
Renovation Potential Report
Calculate renovation costs for an old house online
Are you planning the renovation of an old house and wondering about the real costs? Online calculators provide an initial guidance, but the true cost factors often lie in the details. This guide shows you how to calculate renovation costs based on data and avoid expensive surprises.
With access to Google, BORIS, and Deep Research.
Online calculators provide only a rough estimate; always plan for a buffer of at least 10% for unforeseen expenses.
The costs for a complete renovation range from €400 to over €1,200 per square metre, heavily depending on the year of construction and condition.
State subsidies (KfW, BAFA) can reduce costs by up to 70%, but 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 estimation, a critical question often remains unanswered: How reliable are these figures really? Reality shows that standard calculators can hardly capture the unique building structure, regional price differences, and unforeseen deficiencies. The result is often budget overruns of 20% and more. This article provides you with an accurate, data-driven roadmap. You will learn which cost factors are crucial, how to make optimal use of government funding, and why a data-supported analysis is the only way to achieve a reliable cost estimation.
Online calculators are a useful first step to get a rough idea of renovation costs. They are based on average values and cannot account for the specific conditions of your property. A complete renovation is often priced at €400 to €1,000 per square metre, but this range is vast. For older buildings constructed before 1949, costs can rise to over €1,200 per square metre due to complex building materials.
The greatest risk lies in undiscovered defects such as dampness in the basement or outdated wiring. Experts therefore advise to always plan 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 harmful substances such as asbestos - factors that can quickly increase costs by five-digit amounts. These tools provide guidance but not financial planning security.
A precise calculation must go beyond blanket square metre prices and examine the individual trades. The official construction prices for residential buildings have risen by 3.2% from May 2024 to May 2025 alone, highlighting the need for current data. While a calculator provides a total amount, the real costs consist of many individual items that vary greatly.
Here are typical costs that require a detailed analysis:
Facade insulation: An external thermal insulation composite system (ETICS) costs between €100 and €200 per square metre.
Roof renovation: New insulation and roofing 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, while you should expect to pay between €30,000 and €50,000 for a sustainable heat pump.
Electricity: A complete overhaul of the electrical installation costs between €85 and €130 per square metre.
These numbers illustrate how inaccurate a blanket estimate must be. A detailed analysis of core renovation costs is therefore essential. Only in this way can a realistic budget be set that also takes regional craftsman prices into account.
Energy-efficient refurbishment is the most significant lever for increasing value and reducing operating costs. A comprehensive modernisation can reduce the energy demand of an old building by up to 80%. This not only benefits the environment but also your wallet, as the payback periods for many measures often range from just 8 to 15 years due to high energy prices.
A new heating system alone is often not the most efficient solution. The most effective strategy is to optimise the building envelope before renewing the system technology. Facade insulation can reduce heating costs by about 13%, and a new heating system by 25%. Combining both measures multiplies the savings. When 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.
The government supports energy-efficient refurbishments with substantial grants and loans, which significantly reduce the financial burden. The Federal Funding for Efficient Buildings (BEG) is the central tool here. Key rule: The application must always be submitted before construction work begins. Retroactive funding is excluded.
An overview of the most important funding programmes:
KfW Loan 261: For a complete refurbishment to an efficiency house, there is a loan of up to €150,000 with a repayment subsidy of up to 60%, but a maximum of €90,000.
BAFA Grant (BEG EM): For individual measures such as windows, insulation, or ventilation systems, you receive a grant of 15% on eligible costs up to €60,000. With an individual refurbishment road map (iSFP), the grant increases to 20%.
Heating Exchange: Replacing an old fossil 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 additionally apply for a reduced-interest loan of up to €120,000.
To find the appropriate funding, it is crucial to have a precise understanding of the refurbishment needs. An early assessment, which is possible through an online check for inherited properties, aids in strategic planning.
Renovating old houses involves typical financial pitfalls that can blow any budget. Forward planning based on reliable data minimises these risks. Pay particular attention to the following five points to avoid spending more than necessary.
Ignoring hidden defects: Dampness, dry rot, or asbestos contamination are often overlooked during a superficial inspection. An expert building survey before purchasing or planning is an investment that pays off many times over.
Underestimating regional price differences: The cost of tradesman services can vary by up to 30% depending on the region and demand. Always obtain at least three comparable quotes from local businesses.
Planning changes during construction: Any changes made after construction has begun incur disproportionately high costs. Detailed execution planning before breaking ground prevents expensive adjustments.
Overestimating DIY capabilities: Many homeowners plan to save money through DIY efforts. Often, the time required and necessary expertise are underestimated, leading to delays and construction defects which cost more to fix than the initial savings.
Applying for subsidies incorrectly or too late: Bureaucracy has its pitfalls. Incorrectly completed applications or awarding contracts before approval inevitably lead to subsidy rejections.
A realistic assessment of the renovation costs for an inherited house protects against unpleasant surprises.
You see: The question of how to calculate renovation costs for an old house online has two answers. The quick estimate by an anonymous calculator and the well-founded, data-driven analysis. For a decision of such significance, particularly in the context of an inheritance or a sale, only the second answer provides a secure basis. This is exactly where Auctoa comes in.
Instead of relying on general average values, we access one of the largest real estate databases in Germany. Our AI-supported analysis not only assesses 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 costs involved and the expected increase in value. For heirs and owners, this means: no vague estimates, but a clear, data-based decision-making foundation. You will 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 first assessment.
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 reference point, a thorough analysis is essential for a sustainable financial plan. Considering the individual building structure, 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 eliminate the risk of blanket estimates and provide the necessary security for your investment.
Statistisches Bundesamt offers detailed information on construction prices and property price indices in Germany.
KfW provides information about funding programmes for energy-efficient renovation of existing properties.
Federal Ministry for Economic Affairs provides a comprehensive dossier on the energy transition in the building sector.
German Energy Agency (dena) offers information and guides on the refurbishment of buildings and local spaces.
Consumer Advice Centre provides a guide on suitable renovation of old houses for the future.
Federal Association of Building Materials – Stones and Soils provides information on current topics and developments in the construction industry.
Federal Association of Independent Real Estate and Housing Companies offers information on market activities in the building and housing sector.
Initiative "Building in Existing Structures" provides information and advice on the topic of building in existing structures.
How long does a complete home renovation take?
A core renovation of a single-family home usually takes between three and twelve months. The exact duration depends on the scope of work, coordination of trades, and unforeseen discoveries in the building fabric.
What role does the year of construction play in renovation costs?
The year of construction is a significant indicator. Houses from the 1950s-70s often have poor insulation and outdated technology. Pre-war buildings can additionally have issues with the structure or listed elements that increase costs.
What is an Individual Renovation Roadmap (iSFP)?
An iSFP is a document prepared by a certified energy consultant. It shows the current energy status of your property and lists sensible renovation measures in a logical sequence. With an iSFP, you receive an additional funding bonus of 5% from BAFA.
Can I combine funding options?
Yes, combining funding 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 renovation, refurbishment, and modernization?
A renovation remedies defects and restores the building fabric (e.g. drying out a basement). Refurbishment is a cosmetic improvement (e.g. painting). Modernization improves the standard and energy efficiency (e.g. installation of a heat pump). In practice, these measures often overlap.
How do I find reliable tradespeople for renovation?
Recommendations from architects or energy consultants are a good source. Always obtain at least three detailed quotes and check references. Pay attention to certifications and memberships in trade chambers or professional associations.
