Purchasing a house with an unfinished building or extension: how it is valued
Published 8 November 2026
An unfinished building or extension is valued at purchase based on what the completed property would be worth, from which the costs, time and risk of completion are deducted. The money you have already invested in the building will not therefore be transferred into the price crown-for-crown. What matters is how much value the building has genuinely added and how much work and money remains to be done.
Summary
- The price is based on the value of a completed property minus the costs, time and risk of completion.
- Your own invested costs and hours of work are not the same as added value.
- The legal status of the building has the greatest impact on price: planning permission, registration in the Czech Land Registry and completion certificate.
- The purchase offer is lower than the market price because the buyer bears the risk and completion costs.
- You will receive a written offer with a breakdown of the calculation within 24 hours and it is non-binding.
Basic principle: value after completion minus what remains
An unfinished part is not valued based on what it cost, but on what the next owner will get from it.
Both the valuer and the buyer first determine what the house would sell for when completed and properly certified. Then they deduct the completion costs, which include materials, craftsmen's labour, project documentation and handling of official procedures. They also account for the time during which the house will be unusable and the risks that completion will cost more. Methods and factors are generally described in the article Property valuation: methods and what affects the outcome.
An unfinished part can add value but also take it away. A shell structure in good condition with valid permission is an advantage for the buyer. An unfinished part that needs to be demolished or rebuilt is, on the other hand, a cost.
Completion costs versus added value
Added value is more important for the price than the sum of invoices.
Added value is the difference between the value of the house before building work and the value of the house in its current state. Completion costs are what the buyer will still pay to get the house into a saleable condition. Both are assessed separately.
| Concept | What it means | How it affects the offer |
|---|---|---|
| Invested costs | What you have paid into the building | They do not determine the price on their own |
| Added value | By how much the house has genuinely increased in value due to the work | Increases the offer |
| Completion costs | What still needs to be paid and done | Reduces the offer |
| Risk and time | Budget uncertainty, obtaining permissions, period without use | Reduces the offer |
Example: a completed loft conversion increases the value of the house. If, however, services, plaster and floors are missing and the building has no permission, the buyer may deduct more from the added value than the value of the completed part.
The legal status of a building often matters more than the technical condition
A building without proper permission or registration in the Czech Land Registry (Katastr nemovitostí) is a risk for the buyer, which will be reflected in the price.
Under the Civil Code No. 89/2012 Coll., a building is generally part of the land (§ 506), so an extension is sold together with the house. For the buyer, however, it is essential whether it was built in accordance with decisions or permissions under the Building Code No. 283/2021 Coll. (for older buildings according to previously valid regulations) and whether it is registered in the Czech Land Registry. Registrations are governed by the Land Registry Act No. 256/2013 Coll. For more details on the Land Registry, see our guide Czech Land Registry for property owners.
When assessing, the following is typically examined:
- whether there is building permission or other authority to carry out the building,
- whether it corresponds to the design and actual execution,
- whether the completed part has a completion certificate, and if not, what is missing for certification,
- whether the extension is registered in the Land Registry and corresponds to reality,
- whether there are no mortgages or other charges on the property.
An illegal or unregistered building is not automatically worthless. It does mean time and costs for regularisation and uncertainty about the outcome. The specific procedure for your building will be assessed by the building authority (stavební úřad).
The most common mistakes owners make when estimating value
The most common mistake is to calculate the price as the sum of everything that went into the building, including your own labour.
- Overvaluing your own work. The buyer will not pay for hours spent on the building. They value the result, not your effort, and must assess the quality of the work themselves.
- Confusing costs with value. An expensive solution that the market does not require, for example unusual layouts or non-standard features, will not increase the price proportionally.
- Underestimating completion costs. The final phase, namely services, finishes and certification, are usually the most labour-intensive and most expensive.
- Ignoring defects. Defects hidden under plaster or deviations from the design cannot be seen in a shell structure, and the buyer accounts for them as a risk.
- Missing documentation. Without the design, permissions, building diary and invoices, it is harder to prove the value.
- Delaying the sale. An unfinished building exposed to the weather can lose value over time.
Your own work can, however, be a benefit if it is of good quality and properly documented. It simply does not translate into the price as an hourly rate.
Why the purchase offer is different from the property market price
The purchase offer is lower than the highest possible market price because the buyer takes on the risk, completion costs and time, whilst you get certainty and speed.
On the regular market, you search for a buyer who will appreciate your vision, and the sale can take a long time. Such a buyer often wants to finance through a mortgage, and the bank usually imposes strict conditions for an unfinished building. With a purchase, the buyer takes the building as it is, arranges completion themselves and is responsible for the outcome.
The offer therefore reflects:
- the value of a completed property,
- the costs and time for completion and any regularisation,
- the risk of hidden defects and uncertain budget,
- the speed and certainty of sale without waiting for financing.
With us, you will receive a written offer within 24 hours with a breakdown of the calculation, so you can see how we arrived at the amount. You can get an approximate idea in our purchase price calculator. For general information about purchasing houses in any condition, see more on the House purchase page.
What to do now: documentation and procedure
The fastest way to get a real offer is to prepare documentation about the building and submit a non-binding enquiry.
- Obtain a printout from the Czech Land Registry (Katastr nemovitostí) and check whether the extension is registered.
- Prepare the building permission or other certificates, project documentation and any completion documents.
- Gather invoices, contracts with suppliers and photographs of the current condition.
- Honestly describe what is completed and what is missing, including any known defects.
- State whether there is a mortgage or other charge on the property.
- Complete the form below the article and you will receive a non-binding offer or assessment.
The offer is non-binding and you can withdraw before signing the contract. Payment is made cashlessly through solicitor's escrow, legal services are included in the price and you pay no fees. Upon signing the purchase contract, a deposit of up to CZK 1,000,000 is possible. Ownership passes only upon registration in the Land Registry. Whether and how the sale is taxed should be verified with the Tax Administration or a tax adviser in accordance with Act No. 586/1992 Coll.