Checking variations: variation, BoQ and contract side by side

Anyone who checks a variation (Nachtrag) puts three documents side by side: the variation, the bill of quantities (BoQ) with its preambles, and the contract. Two questions are asked. First, whether the work is really additional or changed, which is the question of entitlement. Second, whether the price demanded is right, which is the question of amount. An AI can prepare a deviation list for this. The assessment stays with the project lead, and this is not legal advice.

On entitlement and on amount

The check on entitlement (dem Grunde nach) clarifies whether the item already belongs to the contractual work or whether there is a change or additional work that the client instructed or caused. The check on amount (der Höhe nach) clarifies whether quantity and price are traceable and how they follow from the contract or from the actual costs.

The legal bases are given here only as source references. Which of them apply depends on the contract. According to the entry at DIN Media (DIN 1961:2016-09), the VOB/B 2016 is still the current edition in November 2026. Whether it has been agreed in your contract, and in which version, is stated in the contract.

Under the VOB/B (German standard contract terms for construction works), the client retains the right to order changes to the design (section 1(3)). The contractor must carry out, on request, work not agreed that becomes necessary for the contractual work (section 1(4)). Section 2 regulates remuneration. Paragraph 5 concerns changes to the design and other instructions from the client: a new price is then to be agreed taking additional and reduced costs into account, preferably before the work is carried out. Paragraph 6 concerns work that the contract does not provide for. It gives rise to a claim for special remuneration, which the contractor must announce before starting the work. Paragraph 3 provides for a price adjustment on request where quantities deviate by more than ten per cent.

Work that the contractor carries out without an order or in unauthorised deviation from the order is in principle not paid for (section 2(8)). It is different if the client recognises it afterwards, or if it was necessary for fulfilling the contract, corresponded to the client’s presumed wishes and was notified to the client without delay.

The official 2016 notice amends the VOB/B only in sections 4, 5 and 8. Section 2 dates from earlier notices. The citations therefore follow the unofficial reading version published by the Federal Ministry for Housing, Urban Development and Building.

In the construction contract under the German Civil Code (Bürgerliches Gesetzbuch, BGB), section 650b regulates the client’s request for a change. The contractor must prepare an offer for the additional or reduced remuneration, but where the change affects the agreed result of the work only if carrying it out is reasonable for the contractor. If the parties do not reach agreement within 30 days of receipt of the request for a change, the client can instruct the change in text form.

Section 650c sets the remuneration for the additional or reduced effort this causes at the costs actually required, with reasonable allowances for general business costs, risk and profit. For the calculation the contractor may fall back on an original price calculation (Urkalkulation) deposited as agreed. For interim payments the contractor can claim 80 per cent of the additional remuneration stated in its offer for as long as there is no agreement and no court decision. The additional remuneration then falls due only after acceptance, and anything overpaid must be returned.

Whether and how these rules take effect in a particular case is for your legal adviser to clarify. For the preparation it is enough to know which data the adviser needs: date of the instruction or announcement, form, start of the work, contract prices, and an original price calculation if one was deposited. The deadlines and duties in a contract can also be pulled out together as a list (see Searching a contract: deadlines and duties as an AI-built list).

What lies side by side

Document	What you need from it
Variation	Items, quantities, unit rates, reasoning, date
Bill of quantities with preambles	Contract items, texts that describe work as already included
Contract	Contract terms, remuneration rules, deadlines, a deposited original price calculation
Correspondence and meeting minutes	Instruction, announcement, dates, form

The deviation list

From these four documents one line per variation item is produced. The language model reads the texts and enters which contract item lies closest to the variation item, whether a preamble already describes the work as included, and where in the correspondence an instruction or announcement can be found. It finds source references in earlier variations, meeting minutes and emails that would be laborious to collect by hand.

The list does not replace reading the variation. It shows where to look closely. A fixed program calculates alongside: quantity times unit rate, deviation from the contract price, totals, quantity deviation from the bill of quantities in per cent. Figures that the program has not confirmed carry the note “unchecked”.

Typical anomalies that such a list shows:

• The variation item resembles a contract item or is already part of its text.
• The quantity deviates from the bill of quantities by more than ten per cent.
• The unit rate is clearly above the contract price of a comparable item.
• An instruction or announcement is missing or is dated after the start of the work.
• The same work appears in two variations.

Every line ends with a query, for example: “Preamble 2.3 lists sealing the penetrations as included, and the variation prices it separately. What is the item based on?” These are questions for the project lead to put to the contractor. They make no statement about the entitlement. Whether the variation is justified, whether the price is reasonable and how to negotiate, you decide.

What this can bring in time

What matters here depends on the role. The contractor submits the variation promptly and before the work is carried out. Site supervision checks entitlement and amount as quickly as possible. In client-side project management the aim is that everything is plausible and correct, so that the client gets a consistent basis for decision on the execution.

The following values are the author’s assumptions, not measured. On average, 45 minutes are assumed for checking in client-side project management, 2 hours for checking in site supervision and 3 hours for the contractor who prepares the variation with reasoning, quantities and calculation. The values apply to the whole handling up to approval. The AI takes over only a part of it: the comparison, the search in the correspondence and the price comparison. For this part, 40 per cent of the work is assumed, together with a time saving of 30 to 60 per cent. Both percentages are assumptions without measurement and without a source. Arithmetically that gives 12 to 24 per cent less time per variation.

todaywith AI preparation

• Check, project managementAssumption, 18 % less

  today 45 min
  with AI preparation 37 min

• Check, site supervisionAssumption, 18 % less

  today 120 min
  with AI preparation 98 min

• Preparation by contractorAssumption, 18 % less

  today 180 min
  with AI preparation 148 min

Source: The author’s working assumption, not measured

Text version of the graphic

• Check, project management: today 45 min, with AI preparation 37 min (Assumption, 18 % less)
• Check, site supervision: today 120 min, with AI preparation 98 min (Assumption, 18 % less)
• Preparation by contractor: today 180 min, with AI preparation 148 min (Assumption, 18 % less)
• Source: The author’s working assumption, not measured

The graphic uses the middle of this range, 18 per cent. In client-side project management that is about 8 minutes per variation, in site supervision about 22 and in preparation about 32 minutes. This remains an assumption. More important than the minutes is what the project lead then has time for: assessing entitlement and price, and talking to the contractor. Whether the assumptions hold for you only shows in your own variations. You then replace them with your own measured values.

How it works in practice

The variation, the relevant section of the bill of quantities, the contract and the related correspondence are enough as input. The deviation list is produced from them. Every note is compared with the original before it is passed on. In a meeting the project lead goes through the lines and decides which queries go to the contractor. The list changes nothing in the figures of the variation, and it does not set a price determination of its own beside them.

1. Gather documents Variation, BoQ with preambles, contract, correspondence
2. Deviation list The AI matches, finds references, words the queries AI prepares
3. Compare prices A fixed program calculates, the language model does not
4. Compare the notes The project lead reads every reference in the original
5. Put the queries The project lead decides what goes to the contractor

Text version of the graphic

• 1. Gather documents: Variation, BoQ with preambles, contract, correspondence
• 2. Deviation list: The AI matches, finds references, words the queries (the AI prepares)
• 3. Compare prices: A fixed program calculates, the language model does not
• 4. Compare the notes: The project lead reads every reference in the original
• 5. Put the queries: The project lead decides what goes to the contractor

The second graphic shows the way from the documents to the query. The AI works only in the second step. How the variation later enters the cost overview is described in Cost monitoring under DIN 276.

What the check does not replace

The check assesses neither entitlement nor price, and it is neither legal advice nor an expert opinion. It does not read drawings, and quantities come from your information. Negotiation and approval stay with you.

Variations contain prices and details about the parties involved. They are processed only on a platform that can be operated in line with the GDPR, not in a consumer chat service. Where names appear in the documents, a data processing agreement (Auftragsverarbeitung) is part of the set-up. Your data protection officer clarifies that.

What you can do now

1. For the next five variations, measure how long comparing, checking and approving take, separately.
2. Decide which documents belong with every variation, and collect them in one place.
3. Check in your contracts whether the VOB/B has been agreed and whether an original price calculation was deposited.
4. Build a template for the deviation list with the columns variation item, contract item, preamble, quantity, price, instruction and query.