01
Geometry is a fact, the deduction is a contract
A wall, a window and a reveal measure the same on every job. What changes is how the contract counts them. A plaster takeoff done under one rule and priced under another is wrong by exactly the difference between the two rules, and nothing in the model will warn you.
That is also why a schedule that returns one net area cannot serve every rule: it reports the area with every opening already subtracted, so a threshold such as “openings up to 2.50 m² are not deducted” cannot be applied afterwards.
02
The three rules in one table
| Rule | Openings kept in the measured area | Clause used by SivaTools |
|---|---|---|
| Türkiye (ÇŞB unit prices) | None. Every opening is deducted. | Unit-price schedule, 15.280.xxxx |
| United Kingdom (RICS NRM2) | Up to 1.00 m² inside the measured area. At the boundary, always deducted. | NRM2 (2013), 3.3.2(2) and Section 28 |
| Germany (DIN 18350 / VOB/C) | Up to 2.50 m², room-height openings included. Reveals are still measured. | DIN 18350:2019-09, 5.2.3 and 5.3.1 |
| Spain (common criterion) | 50% deducted between 2 and 4 m², 100% above. A function, not a threshold. | Custom rule with a partial-deduction band |
Confirm every figure against the current edition of the standard and your own contract. Clause numbers above are the ones SivaTools cites in its reports.
03
What the difference is worth on a real model
The demo project is a two-storey building with 22 rooms, 344 plaster shells, 1,118.28 m² of net area and 90 opening records. Run once, then priced under each rule:
| Rule | Openings kept in | Added to billable |
|---|---|---|
| Türkiye | 0 | 0.00 m² |
| RICS NRM2 | 12 | +6.75 m² |
| DIN 18350 | 74 | +122.02 m² |
Under DIN 18350 the billable quantity is 10.9% larger than under the Turkish rule, from the same geometry. A takeoff that could only produce the Turkish figure would be systematically low on a German job.
04
How to protect yourself when you bid or bill
- Read which rule the contract names before you take anything off, and write it at the top of the takeoff.
- Report the physical area, the billable area and the difference side by side, so the clause has a visible price.
- Keep reveals as their own line. They are real plastered surface that a deduction silently removes.
- Record how many openings were kept and how many could not be measured and were therefore deducted.
- State what you did not apply. Two DIN sub-rules, the 30 cm column and beam interruptions and the smallest-enclosing-rectangle provision, are not applied by SivaTools, and its report says so on every run.
05
Applying the rule inside Revit
SivaTools measures each opening on its own, which is what makes a threshold rule applicable at all. You choose Türkiye, NRM2, DIN 18350 or a Custom rule, and the report and CSV print the rule, the clause, the threshold and the counts. With the Turkish rule selected, which is the default, the output is unchanged from earlier versions.
SivaTools is configured according to these rules, not certified against them by RICS, DIN or anyone else, and it does not ship the text of any standard.