For one home extension With a basic stone construction, a 10 m² area can be expected to cost around €23,000 including VAT. For 20 m², that figure is around €42,000. These are general market indications for basic construction. For a fully finished extension, this includes the entryways, installations, and interior finishing. The cost of your plans depends on the existing home and the design you choose.
Van der Hart Timmerwerk We can handle the entire process: from design, drafting, construction calculations and permit application to construction, installations and complete finishing. You have one single point of contact and the work is coordinated accordingly. Together we look at what suits your home, your living needs and your budget.
Indicative starting prices for an extension
The amounts below provide an initial overview of the costs of a complete stone extension. They help with orientation, but do not yet tell you what a fully finished living room or kitchen costs.
| Dimensions: width × depth | Surface area | Indicative starting price for casco, including VAT |
|---|---|---|
| 5 × 2 meters | 10 m² | Starting at around €23,000 |
| 4 × 3 meters | 12 m² | Starting from around €25,000 |
| 5 × 3 meters | 15 m² | Starting from about €36,000 |
| 5 × 4 meters | 20 m² | Starting from around €42,000 |
The amounts have been rounded off based on the minimum thresholds in the Cost overview of Vereniging Eigen Huis, That price level applies for 2027. It concerns the basic construction, excluding any additional features, finishing, installations and furnishings. These are not fixed rates Van der Hart Timmerwerk. Your home’s quote may be higher.
How much does a extension cost per square meter?
The mentioned base price for a 20 m² house comes to approximately €2,100 per m². Use this as a rough estimate. The price of a different size cannot be calculated automatically with the same amount. Even a small extension requires preparation, connections, and work on the existing house.
How much does a fully finished extension cost?
The total price of a finished extension is higher than the base price. In addition to the new exterior, it involves connecting to your home and installing the facilities that make the space comfortable to use. This includes the facade opening, heating, sockets, plastering, and floor finishing.
What falls under the scope of a complete renovation or renovation work varies from proposal to proposal. Therefore, we will discuss in detail what you would like to have done. Do you only want the extra space to be finished, or do you also want to include the floor and walls in the existing living room? A new kitchen, underfloor heating, and painting can also be part of the overall plan.
Calculation example: a finished extension of 20 m²
You enlarge the living room with a 5 × 4 meter extension, with a flat roof and standard front door.
| Part | Amount accepted |
|---|---|
| Casco construction, including groundwork, foundations, insulated floor, exterior walls, roof and facade | €45.000 |
| Facade opening including supporting structure | €5.000 |
| Installations, plasterwork, painting and floor finishing in the extension, including repairs around the window opening | €15.000 |
| Design, drafting, construction calculations and any application for permits and fees | €5.000 |
| Estimated amount before reserve | €70.000 |
| Selected reserve of 10% | €7.000 |
| Total available budget | €77.000 |
The amounts below are hypothetical assumptions; they are not average market prices or quotes from Van der Hart Timmerwerk.
All amounts are inclusive of VAT, where applicable. The starting point is suitable soil and foundations without concrete foundations. A new kitchen, light street, garden renovation, temporary accommodation and a new floor in the existing living room are not included.
The actual costs and required reserve may vary. For your property, we will work out the desired design in a suitable quote.
Which choices determine the cost of your extension?
The foundation and the existing facade
The new construction must fit the ground, the load, and the existing house. For example, whether a concrete foundation is needed must be assessed beforehand. The size of the opening to the living room or kitchen also has an impact on the work.
A wide, open connection may require a different supporting structure than a smaller passage. During the preparation phase, we use the necessary surveys and structural calculations to determine what is technically necessary. This way, we can clearly identify which solution suits your home and what that means for the budget.
The dimensions and layout
How much extra space do you need for your living needs? A simple floor plan helps to determine that. Draw the dining table, seating area, or kitchen and see how much space you have left to walk comfortably.
We also look at the existing layout. Will the kitchen remain in the same location or do you want to move it? And are there any adjustments needed to other spaces? These choices are part of the plan before the dimensions become final.
Frames, glass and daylight
A sliding door, French doors or a light street have each a different look and price. The choice also depends on how you use the space and how much daylight you want to keep in the existing part of the house.
Discuss which components are important to you. For example, by working out two versions of a door or a design with and without a light strip, you can see how those choices add to the budget.
Installations and the transition between old and new
Underground heating, lighting, power sockets and kitchen pipes are all given a place during the preparation phase. This way, the construction and installation work can be carried out in the correct order.
The finish of the existing living room also counts. A new floor or a plastered ceiling does not always stop at the edge of the extension. Therefore, we discuss which part of the house is included, so that the new space fits nicely into what is already there.
If you want to tackle multiple spaces at the same time, we can combine the extension with the renovating your house.
Which activities are included in the total budget?
When developing the budget, we look beyond the additional square meters. Depending on your home and plans, these components may include the following:
- Design, construction drawings and structural calculations.
- Soil testing, groundwork and the necessary foundation.
- Application for a permit and any municipal fees.
- Demolition work, facade opening and supporting structure.
- Windows, glazing, roofing and insulation.
- Plumbing, heating, electricity and ventilation.
- Kitchen placement, floor finishing, plastering and painting.
- Repair of adjoining parts of the house and the terrace.
The parts we cover are specified in advance. Work that is already included in the construction cost doesn’t need to be counted separately. Any additional expenses, such as temporary accommodation or new furniture, should be included in your personal budget.
Design, permit and execution in one plan
A lot is possible, but the existing structure, available space, and regulations at your location determine which plans are feasible. Therefore, we first review the property and your wishes. Then we coordinate the design, calculations, and further preparations.
Via the Permit check of the Environment and Planning Portal Can you determine which steps are required for your address? An application for a permit may be part of our process. Even if you are allowed to build without a permit, building regulations still apply.
How do you keep control of costs?
Start with what the expansion is intended to solve for you. Do you want a larger living room, more natural light, or a spacious kitchen? If your priorities are clear, we can work together to think about the layout and material choices in a focused way.
Let the parts you are unsure about be billed separately. This way you can choose whether you want to include a light track, other windows, or custom-made accessories. Make those choices as much as possible before the installation begins.
A provisional amount has been included in a set of items for a component that is not yet completely fixed. Discuss which implementation is included and how a deviation will be accounted for. For changes during construction, we first clarify the implications for price and schedule.
Your development in Central Netherlands, from initial idea to completion
Do you live in Central Netherlands and would you like more space in your home? From Uithoorn we are happy to visit you. We listen to your ideas, look at the existing property and discuss how you want to use the extra space.
Whether you want a complete extension or a fully finished living space: Van der Hart Timmerwerk keep track of the entire process. With coordinated work, one fixed point of contact and clear agreements, you know exactly what’s going on.
Curious about what your extension will cost? Discuss your plans and request a free quote. Feel free to send us photos, global dimensions or an existing drawing. That way, we can work together with you to discuss the possibilities and budget in more detail.
