Calculating the residual value: what may an attic in Vienna cost?
The residual value works backwards: what does the finished project bring in, what does it cost to build and finance, and which profit has to remain? What is left is the most the purchase may cost — including transfer tax, fees and the financing it triggers itself. That is how ÖNORM B 1802-3 describes it for property that is yet to be built on.
Worked exampleBurggasse 11, 1070: building class III, measured eaves 13.9 m. An attic conversion yields 287 m² of usable area. At a sale price of 8,500 €/m² in the attic, construction costs of 3,000 €/m² and 10 % profit, the attic may cost 320,000 to 610,000 € — about 1,130 to 2,120 € per m² of usable area. Without profit the calculation breaks even from 5,800 €/m² sale price.
What may the attic at your address cost? Type the address — Azima reads building class and eaves and calculates residual value, break-even and return; every assumption can be overwritten.
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How the residual value method calculates
- Revenue: the new usable area times the sale price — default 5,500 €/m² on a standard floor and 8,500 €/m² in the attic. The attic price is a default, not a documented Vienna figure; in Azima the district's median purchase price (Statistics Austria) is the starting point.
- Costs: construction 3,000 €/m² of gross floor area, plus surcharges for fees, planning, structural engineering, marketing and a reserve, plus financing (80 % debt at 4.5 %, 24 months).
- Profit: 10 % of revenue — the literature names 5 to 10 %.
- What remains is the residual value: the highest purchase price at which this profit stays, with acquisition costs (8.6 %) and the financing of the purchase included.
Why the residual value is a range
Construction costs are the most uncertain large figure — expert values range from about 2,400 to 4,300 €/m². That is why the residual value here is shown for construction costs 10 % higher to 10 % lower. And the standard itself calls the method sensitive: in its example, 15 % more revenue raises the value by half.
Two houses, calculated
With the defaults above, attic-conversion scenario, purchase price as the unknown. Bloch-Bauer-Promenade 8, 1100 has the smaller footprint — hence the smaller range at almost the same price per m².
What the market pays for attics
Analyses of purchase contracts put raw attics in Vienna at 1,000 to 1,200 € per m² of achievable usable area without a building permit and 1,350 to 2,200 € with one — the data run to 2021 and have not been republished since. If the residual value lies below, the conversion does not carry the market price under these assumptions; if it lies above, more than the target margin remains under these assumptions.
What the calculation does not know
Rough calculation from the areas of the potential and the stated assumptions — no valuation, no expert opinion, no financing commitment. Not included: condition and statics of the existing building, existing leases, requirements from protection zones or listed-building status, contaminated sites, subsidies, VAT and income taxes, price development over the term. Interest is calculated on half the loan over the term (average drawdown). Construction cost 3,000 €/m² GFA: residential construction costs in Vienna as recommended by court-appointed experts (TU Wien 2025), indexed to August 2026 with the Statistics Austria construction cost index, range about 2,400 to 4,300 €; interest 4.5 %: 3-month Euribor September 2026 (2.64 %, ECB) plus 2 percentage points; margin 10 % of revenue (literature: 5 to 10 %); other defaults as in common developer calculations (as of 9 Oct 2026); revenue anchor from the district's median purchase price (Statistics Austria, land register), the attic premium is a default, not a documented Vienna figure; parking obligation by the zone of the Vienna Garage Act 2008; compensation levy under § 54 WGarG — the current rate is published by the City of Vienna. Reference values as of 12 Oct 2026.
Frequently asked
What is the residual value?
The highest price a plot or an attic may cost so that a project still yields the planned profit after all costs. It is calculated backwards from revenue (residual value method, ÖNORM B 1802-3).
How do you calculate the residual value?
Revenue of the finished project minus construction, ancillary and financing costs minus profit; what remains, less the costs the purchase itself triggers (transfer tax, registration, contract, commission, financing), is the residual value. Here with 10 % profit on revenue.
What may an attic in Vienna cost?
It depends on building class, eaves and sale price. For Burggasse 11, 1070 (building class III) the calculation gives 320,000 to 610,000 € for 287 m² of usable area, about 1,130 to 2,120 € per m². Purchase-contract analyses name 1,000–1,200 € per m² without and 1,350–2,200 € with a permit (data to 2021).
Why is the result so sensitive?
Because the residual value is the difference of large numbers: a few per cent on revenue or construction costs move the remainder a lot. The standard says so itself — in its example 15 % more revenue raises the value by half. That is why it is shown here as a range.
Is this a valuation?
No. It is a rough calculation from open data and stated assumptions — no valuation, no appraisal, no financing commitment.
Sources: Construction cost 3,000 €/m² GFA: residential construction costs in Vienna as recommended by court-appointed experts (TU Wien 2025), indexed to August 2026 with the Statistics Austria construction cost index, range about 2,400 to 4,300 €; interest 4.5 %: 3-month Euribor September 2026 (2.64 %, ECB) plus 2 percentage points; margin 10 % of revenue (literature: 5 to 10 %); other defaults as in common developer calculations (as of 9 Oct 2026); revenue anchor from the district's median purchase price (Statistics Austria, land register), the attic premium is a default, not a documented Vienna figure; parking obligation by the zone of the Vienna Garage Act 2008; compensation levy under § 54 WGarG — the current rate is published by the City of Vienna. Reference values as of 12 Oct 2026. · Residual value method: ÖNORM B 1802-3 · Attic market range: Rustler, analyses of purchase contracts, published 2019–2022, data to 2021 · Houses: Stadt Wien — Generalisiertes Dachmodell LOD2.1 (CityGML), data.wien.gv.at, CC BY 4.0 · Stadt Wien — Generalisierte Flächenwidmung und Zonen (OGD-WFS), Abruf 2026-09-23, data.wien.gv.at, CC BY 4.0 · Stadt Wien — Bezirksgrenzen, data.wien.gv.at, CC BY 4.0. Calculation: src/lib/kalkulation.ts, the same as in the developer-calculation chapter. Not a valuation.
Attic conversion in Vienna · What the house still allows · For agents and developers