Should the construction-installation cost in a design estimate carry provisional sums? — the stage division of provisional sums (BOQ/contract level) vs reserve funds (estimate level)

Topic Positioning

A frequent estimate-preparation and review question: should the works cost (construction-installation) of a design estimate carry "provisional sums"? Answer: no. Provisional sums are a contract-price management tool of the BOQ system, at a different stage and cost basis from design estimates; the design-stage "uncertain/unforeseeable" function is carried by the total-estimate reserve funds.

Core Conclusions

1. Provisional sums are contract-price tools, not design-stage investment accounts. GB/T 50500-2024, 2.0.13: "Provisional sum: an amount the employer tentatively includes in the BOQ and contract price for works, services, or price adjustments not yet determined or detailed at tendering." Used wholly or partly per employer instructions; if unused, deducted from the contract price. Three keywords: BOQ, contract price, at tendering.

2. The standard's scope excludes the design-estimate stage. 1.0.2: "This standard applies to pricing activities of construction tendering and implementation. Other pricing activities may refer to it." (Tendering, construction, completion, disputes; EPC may refer where compliant.) Design estimates are investment documents of the preliminary design stage — outside the scope.

3. Employer-controlled; unused portions revert. 8.3.1: "Provisional sums within the contract price are controlled by the employer and used per employer instructions. Though in the contract price, they do not belong to the contractor and may not occur; only amounts actually incurred per contract become contractor entitlements in settlement; unused sums revert to the employer at completion." A contract-level reserve, not a design-stage account.

4. The estimate's own composition has no such account. T/ZBD 100.3-2022, 4.1.1: "The total investment estimate generally comprises works costs, other construction costs, reserve funds, construction-period loan interest, and VAT; works costs comprise building, equipment purchase, and installation; productive projects add working capital." Annex A's table (works costs -> other costs -> reserves (basic, price-difference) -> interest) lists no "provisional sum" (VAT is a pass-through, forming no asset).

5. Sector compilation methods likewise have none. Railway TB 10801-2024: costs comprise construction-installation (direct + indirect), equipment purchase, other costs, VAT, basic reserve, price-difference reserve, and construction-period loan interest; the sixteen-step single-estimate program (base labor/materials/machinery -> direct works -> transport outside price -> price difference -> filler -> direct -> construction measures -> special increases -> direct -> indirect -> estimate value) contains no provisional-sum account.

6. Concept clarification: "BOQ unit-rate method" estimates add no provisional sums either. Estimate methods are the indicator method, quota method, and BOQ unit-rate method (T/ZBD 100.3-2022, 4.5.1). The unit-rate method changes only the pricing of units; the summary structure remains "works + other + reserve + interest" — the quota-method flow (4.5.4) likewise adds no provisional-sum tier.

7. The design-stage function is carried by reserve funds. Annex E item 13: "Reserve funds: amounts reserved at the estimate stage for unforeseeable design changes, negotiations, natural-disaster handling, defect repair, underground obstacles, oversized equipment transport, and price/exchange movements during construction." Item 14 basic reserves (changes, negotiations, disasters, repairs, unforeseen obstacles, over-dimension transport); item 15 price-difference reserves (price and exchange movements). The contract-level "uncertain/unforeseeable" function of provisional sums is carried at design stage by total-estimate reserves — different systems and stages, never mixed or double-counted.

Applicable Boundaries

• For standard-caliber design estimate preparation and review; sector/local estimate methods or contract documents govern where they expressly provide.
• In BOQ pricing (tendering, construction, settlement), provisional sums remain in the contract price, employer-controlled, unused portions reverting — unchanged by this card.
• Reserves (estimate caliber) and provisional sums (BOQ caliber) are similar but not interchangeable and must not be double-counted in one investment document.
• EPC may refer to GB/T 50500-2024 rules, but the estimate caliber follows the applicable estimate method (T/ZBD 100.3-2022 and sector methods).

Further Reading

• GB/T 50500-2024, 2.0.13, 1.0.2, 8.3.1.
• T/ZBD 100.3-2022, 4.1.1, 4.5.1/4.5.4, Annexes A and E.
• TB 10801-2024, Section 2.6 (Figs./Tables 2.6.1-2.6.3).
• Local official pages (extended verification):
  • http://zjj.rizhao.gov.cn/art/2013/5/15/art_175554_10010422.html
  • http://zjj.rizhao.gov.cn/art/2016/6/30/art_175554_10010565.html
  • https://zjt.jiangxi.gov.cn/jxszfhcxjst/flfgg/pc/content/content_1765232414866206720.html
  • https://zjt.jiangxi.gov.cn/jxszfhcxjst/flfgg/pc/content/content_1765231460351668224.html
  • https://zjt.jiangxi.gov.cn/jxszfhcxjst/flfgg/pc/content/content_1765229908383690752.html
  • https://zjt.jiangxi.gov.cn/jxszfhcxjst/wjtz/pc/content/content_1939613104680411136.html
  • https://zjw.sh.gov.cn/gfxwj/20250925/ff9777cd46d2433b99e29968f794a786.html
  • https://cjw.ezhou.gov.cn/zfxxgk_4836/zc/wjtz/202509/t20250923_726897.html
  • https://zjj.zhuhai.gov.cn/zjj/gzhd/ywzsk/szl/content/post_3865233.html
  • http://jsj.cngy.gov.cn/collect/result/20231207115147577.html