The cost of one roof extension They depend on your property, the dimensions and the desired finish. As a first calculation example, for a prefabricated structure on a suitable concrete flat roof, you can start from a publicly offered starting price of approximately €2,000 per m² including VAT. At 30 m², that amounts to €60,000. Preparation, any structural reinforcement, and the further interior finishing can be added to that.
An extra bedroom for the children, a quiet work area or an own floor with bathroom: we are happy to help you with your plans. We Van der Hart Timmerwerk can arrange the entire process for you, from drafting and permitting to construction, installations and finishing. Together we will look at what suits your home, your wishes and your budget.
Costs of a roof construction per m² and area
The table below shows what different surfaces mean in a basic calculation price of €2,000 per m², including VAT.
| Surface roof construction | Insurance calculation example including VAT |
|---|---|
| 20 m² | €40.000 |
| 30 m² | €60.000 |
| 40 m² | €80.000 |
| 50 m² | €100.000 |
These are sample calculations; they do not represent average total prices or rates Van der Hart Timmerwerk. The calculation is based on an open-source basic cost estimate for a suitable concrete flat roof. This is not a complete budget for a finished floor. For a smaller build, a different roof construction or additional customization, the price per m² may also vary.
Also ask how the area is measured. A 30 m² build based on external dimensions yields less than 30 m² of usable interior space. Exterior walls, interior walls, and the stairwell take up space. Therefore, also check whether the rooms you want to create actually fit into the design.
What does a fully finished roof structure cost?
A fully finished roof structure requires a higher budget than just the basic construction. How much higher depends on the layout, installations, and finishing. Two bedrooms with an attic require a different budget than a bedroom with a full bathroom.
What is covered by the casco?
With a casco, it usually concerns the foundation of the structure: the load-bearing structure, exterior walls, windows and the roof. What exactly is included varies per provider. Therefore, please describe how insulation, glazing, roofing and the connection to the existing house are included.
Also check whether the construction of the stairwell, the stairs and the preparatory installation work are included. The word ‘casco’ alone is not sufficient to compare two quotes.
What interior finish is included?
For usable rooms, you need interior walls, interior doors, electrical wiring, heating and ventilation, followed by the agreed finishing of walls and ceilings, plastering and any floor finishing.
Painting, floor finishing, sanitary equipment and a complete bathroom are also available. We coordinate the professionals and the work to ensure that everything is done to your satisfaction. The quote will include details about how we will complete the renovation so that you know in advance what finishing touches are included.
Calculation example: a finished roof structure of 30 m²
For a 30 m² roof construction with two bedrooms and a mezzanine, the below fictional budget shows how to build a total budget.
The amounts are calculated figures, not average market prices or quotes Van der Hart Timmerwerk.
| Part | Calculation amount |
|---|---|
| Cover construction, including stairs, stairwell, crane and scaffolding | €60.000 |
| Interior walls, doors, installations, plasterwork, painting and floor finishing | €20.000 |
| Drawing, construction calculations, permit application and fees | €6.000 |
| Subtotal | €86.000 |
| Selected reserve of 10% | €8.600 |
| Total sample budget | €94.600 |
Prices include VAT where applicable. The example assumes a suitable existing support structure, without reinforcement, bathroom, roof terrace, relocation of solar panels or temporary accommodation. The actual costs and required reserve depend on your property and preferences.
What determines the price of your roof construction?
The carrying capacity of your home
An additional floor adds weight to the existing house. A builder assesses how the structural support and foundation can withstand that load. Sometimes reinforcements are needed before the construction can be made.
The constructive research and the necessary calculations are part of the preparation we can provide for you. The results determine which adjustments are included in the plan and budget.
The existing roof and the way it was built
Complete floor elevation on a flat roof differs from raising a pitched roof. The demolition work, the new construction and the connections are different. Therefore, the calculation examples in the table cannot be used directly for every roof elevation.
In the case of prefabricated construction, building components are pre-made. In construction on site, the construction is built on site. Which approach is appropriate depends on the design, the home, and accessibility. Compare the total work involved: a short installation time does not indicate how much preparation and interior finishing is required.
Do you especially want more headroom in the attic? Then read about the Difference between a roof extension and a roof construction. A smaller renovation can sometimes provide enough space.
The staircase and the floor below
The new floor should be easily accessible. The location of the stairs determines how you get upstairs and what space you need on the floor below.
In the design, we consider both floors together. During the execution, we also take into account the stairwell, the staircase, and the agreed restoration of adjacent floors, walls, and ceilings. This way, the new floor seamlessly connects with the rest of your house.
Bathroom, installations and material selection
If you want a bathroom upstairs, then water pipes, drainage and ventilation must all be included in the design. The route through the existing house is part of the design. The same applies to heating, lighting and power outlets.
In addition, window frames, facade cladding and roof edges also determine the final design. We are happy to work with you on materials and details that suit your home. By discussing the exterior and interior finishes simultaneously, the work can be coordinated well.
Accessibility and facilities on the roof
Where can a crane be placed? How are materials lifted? And what scaffolding or facilities on the street are needed? Discuss accessibility before the execution is budgeted.
Solar panels, roof penetrations and existing installations can also affect the work. Keep a record of which parts are being removed, modified or repositioned.
What additional costs should you take into account?
When receiving a price quote, check whether the following components are already included:
- Design, construction drawings and structural calculations.
- Research and possible strengthening of the existing home.
- Application for a permit and municipal fees.
- Demolition work, crane, scaffolding and removal of construction waste.
- Staircase, trap hole and renovation work on the existing floor.
- Installations and modifications to existing roof systems.
- Interior finishing, painting, floor and possibly bathroom.
- Temporary stay or storage, when necessary.
Not everything is automatically included in the construction cost. Some parts are already included. Therefore, please ask by post what is included and what is still outstanding.
Is there a set price in the quote? That is an estimated amount for a part whose costs have not yet been finalized. Ask what the corresponding options are and how a difference with the actual costs will be accounted for. Also keep a reserve for unforeseen work, appropriate to the uncertainties that remain after the preliminary investigation.
Permit and preparation are part of the budget
When constructing a roof, a permit process must be taken into account. The application, the required drawings and the construction calculations can also be part of our assignment. We coordinate the preparation and check which technical and spatial regulations apply to your home. Among other things, the load-bearing structure, building height and appearance determine what is possible.
It Information Point Living Environment provides an explanation of the technical licensing requirement. Through the Environmental Office You can do the Permit Check for your address. Include drawing work, calculations, and any fees from the beginning in the budget.
How do you keep control of costs?
Start with the space you need and the budget you have available for it. Discuss what requirements are essential and where you can still make choices. This way, the design can be adjusted accordingly before all the details are finalized.
Then compare the offers based on the same specifications, materials, and delivery date. A lower price means little if the stairs, installations, or finishing touches are missing. Have changes during construction recorded in advance, including the impact on price and schedule.
Take a look at our home renovation with roof construction in Uithoorn. There, the construction was combined with a renewed facade. With such a project, the budget involves more than just the new space above: the work on the existing house also counts.
Curious about what a roof extension costs for your home?
Whether you want an extra bedroom or a complete floor with bathroom: we are happy to work with you to explore how to make the most of the space above your home. You have a Van der Hart Timmerwerk single point of contact for the preparation, construction, and agreed finishing work. This way, you don’t have to coordinate the various tasks yourself.
From Uithoorn, we work in the middle of the Netherlands, including in Amstelveen, Aalsmeer, Amsterdam and Haarlem. If you want to know what is possible for your home and what budget fits, feel free to send us photos, existing drawings or a sketch.
Tell us how you want to use the extra space. Discuss your roof construction and request a free quote. Then we translate your wishes into a suitable plan with clear arrangements regarding execution and costs.
