Start with a clear baseline
Assume a home worth €450,000 with 100 m² of living space: an average of €4,500 per existing square metre. This is not a separate selling price for added space; location, house type, layout and condition are combined in the home’s value. Use it only as a starting point for sensitivity analysis.
Use the extension’s internal area
External dimensions of 6 by 3 metres yield about 14.58 m² internally in the three-wall, 30 cm model. We use three chosen percentages of the existing value per metre. They are assumptions to illustrate sensitivity, not market averages or forecasts.
| Calculation assumption | Calculated value effect | Calculated new home value |
|---|---|---|
| 60% | €39,366 | €489,366 |
| 80% | €52,488 | €502,488 |
| 100% | €65,610 | €515,610 |
Compare against the full construction budget
With an assumed full budget of €60,000, the middle scenario gives €52,488 minus €60,000: negative €7,512. That is not a realised loss, just as a positive difference is not profit. It compares assumptions and excludes financing, taxes, selling costs and market changes.
Assess what improves your particular home
Discuss the layout against comparable homes with a local agent or valuer. Added space may solve a problem but reduce a desirable garden or daylight. Kadaster points to agents or valuers for current property values. The calculator primarily helps you ask better questions.