Most developers waste money at one of two points: they commission a detailed cost plan when all they needed was a feasibility study — or they skip proper cost planning entirely and get ambushed by a tender price that blows their budget.
The difference between a feasibility study and a detailed cost plan isn’t just a matter of depth. It’s a matter of timing, purpose, and what decisions you’re trying to make. Use the wrong tool at the wrong stage and you’re either overspending on reports you don’t need yet, or building on foundations of guesswork that will cost you far more later.
This guide explains both reports clearly — what they contain, when you need them, and how they fit into the RIBA plan of work that governs UK construction projects from concept through to completion.
What Is a Feasibility Study in Construction?
A feasibility study is the earliest form of cost intelligence on a development project. Its purpose is simple: can this project be built for a budget that makes financial sense?
At this stage, you don’t have detailed drawings. You might have a site, a concept, and some initial thoughts about what you want to build. The feasibility study takes that information and produces an order-of-magnitude cost assessment — enough to tell you whether the project is worth pursuing, whether your budget assumptions are realistic, and whether you should commission an architect to develop the design further.
A construction feasibility study typically includes:
- Gross Development Value (GDV) assumptions and sensitivity analysis
- Elemental cost estimate based on benchmark rates (£/m² by building type and region)
- High-level breakdown by major cost category — substructure, superstructure, finishes, services, externals
- Preliminary and contingency allowances
- Professional fees estimate (architect, structural engineer, QS, planning)
- Abnormal cost flags — known site-specific risks that need investigation
- Programme outline and cash flow assumptions
- Viability summary — does the project stack up at current build costs and values?
What a feasibility study is not: it is not a measured cost plan, it does not use drawn quantities, and it does not provide the detail needed to appoint a contractor or go to tender. Its accuracy is typically plus or minus 20–30% — which sounds imprecise, but is entirely appropriate for the stage at which decisions are being made.
For a developer assessing whether to buy a site, or a client deciding whether to proceed with planning, a well-constructed feasibility study is worth its weight in gold. It protects you from committing significant money to a project that was never financially viable.
What Is a Detailed Cost Plan?
A detailed cost plan is a fully measured, line-by-line cost schedule prepared from developed or technical design drawings. It is the primary cost management tool for the construction phase of a project and the foundation for contractor tendering.
Where a feasibility study asks “is this viable?”, a detailed cost plan answers “what exactly will this cost, and why?”
A detailed cost plan — or detailed schedule of costs UK — includes:
- Full measured quantities for every trade section, taken from coordinated construction drawings
- Labour and materials split on every line item — no blended rates hiding your cost base
- Subcontractor pricing for specialist packages (MEP, structural steel, specialist finishes)
- Attendance and profit on subcontract works
- Detailed preliminaries schedule — time-related and fixed items, not a lump sum
- Risk register and contingency allocation by trade
- Provisional sums clearly identified and justified
- Exclusions list — what’s not in the number and why
- Summary and comparison against approved budget
A detailed cost plan is structured to RICS NRM2 (New Rules of Measurement 2) — the UK standard for building works cost planning and bills of quantities. This ensures the document is consistent, auditable, and usable by all parties in the tender and contract process.
The accuracy of a detailed cost plan is typically plus or minus 5–10% on a well-designed project with a complete drawing package. That level of accuracy is what you need before appointing a contractor and committing to a construction contract.
RIBA Cost Planning Stages — When Each Report Is Needed
The RIBA Plan of Work provides the framework for how construction projects are designed and delivered in the UK. Cost planning runs in parallel with the design stages, and the type of cost report you need changes at each stage.
RIBA Stage 1 — Preparation and Briefing (Feasibility)
This is where the project starts. The client has identified a need, a site, or an opportunity. Drawings don’t exist yet — only a brief and some initial thinking about scale and scope.
Cost report needed: Feasibility Study / Order of Cost Estimate
Purpose: Establish whether the project is financially viable before any design fees are committed. Based on gross floor area benchmarks and regional cost factors. Accuracy: ±25–30%.
RIBA Stage 2 — Concept Design
The architect has produced initial concept drawings. The overall form, massing, and basic layout of the building are established. Structure and services have been considered at a high level.
Cost report needed: Elemental Cost Plan (Stage 2 Cost Plan)
Purpose: Confirm the concept design is deliverable within the approved budget. Identify any elements where the design is running over cost benchmarks. Based on elemental breakdown (substructure, envelope, finishes, services, externals). Accuracy: ±15–20%.
RIBA Stage 3 — Spatial Coordination
The design is now coordinated between architect, structural engineer, and services engineers. The layout is fixed. Structural solutions are confirmed. The building looks like a building.
Cost report needed: Developed Cost Plan (Stage 3 Cost Plan)
Purpose: Confirm the coordinated design is still within budget. Flag value engineering opportunities before the design is frozen. Based on measured quantities from Stage 3 drawings. Accuracy: ±10%.
RIBA Stage 4 — Technical Design
All construction information is produced. Specification is written. Drawings are complete and fully coordinated. This is the information package that goes to tender.
Cost report needed: Detailed Cost Plan / Pre-Tender Estimate / Full BOQ
Purpose: Provide a robust pre-tender cost check and, where required, a full Bill of Quantities for contractor tendering. This is the document that underpins the construction contract. Accuracy: ±5–10%.
When Developers Need Each Report — The Decision Points
Understanding the theory is one thing. Knowing when to commission what in the real world is where most developers get tripped up.
Site Purchase Decision
Need: Feasibility Study
Before you bid on a site or sign a purchase contract, you need a viability number. The feasibility study tells you what the build will cost, what the completed development is worth, and whether the land price makes sense. Many developers skip this and rely on their own gut feel — and many developers have bought sites that were never viable as a result.
Planning Application
Need: Stage 2 Cost Plan
If your planning application needs to demonstrate viability (as required under Community Infrastructure Levy assessments or affordable housing obligations), you need a properly structured cost plan at Stage 2. Planners are increasingly sophisticated — a rough builder’s estimate won’t cut it.
Funding / Finance Application
Need: Stage 3 Cost Plan at minimum, Stage 4 if available
Development finance lenders — whether bank, bridging, or private — require a robust cost plan before releasing funds. Most lenders also appoint a monitoring surveyor who will benchmark your QS’s figures against their own data. If your cost plan is vague or incomplete, it raises red flags and delays drawdown.
Going to Tender
Need: Stage 4 Detailed Cost Plan / Full BOQ
This is where detailed measurement and proper BOQ preparation become non-negotiable. Without a full BOQ, contractors price their own quantities — and they all price different quantities, making tender comparison meaningless. With a QS-prepared BOQ, all tenderers price the same document, and your QS can identify why bids differ and where savings are achievable.
Why Early Cost Planning Saves Developers Serious Money
The cost of changing your mind increases exponentially as a project advances. This is sometimes called the “cost of change curve” — and it’s real.
A decision made at feasibility stage that avoids an over-budget specification costs nothing. The same decision made at Stage 3 costs design fees for redesign. Made at Stage 4, it costs design fees plus delays. Made after contract award, it triggers a formal variation — which the contractor prices at the worst possible moment, with maximum leverage.
Here are some real examples of where early cost planning makes the difference:
- Specification creep: A developer approves a concept design that looks stunning. By Stage 3, the architect’s specification has added underfloor heating, feature lighting, natural stone throughout, and bespoke joinery. The cost plan comes back £180,000 over budget. Had the Stage 2 cost plan been prepared and reviewed rigorously, the specification would have been managed from the start.
- Structural surprises: A feasibility study on a conversion project flags an abnormal cost risk around existing structural steelwork. The developer investigates, discovers the steelwork needs full replacement, and reprices the project — before exchange of contracts. Without the feasibility study, they would have discovered this after purchase.
- Tender shock: A developer goes to tender without a pre-tender estimate. Tenders come back £300,000 above budget. There are no benchmarks to identify which trades are over-priced, no BOQ to negotiate against. The project stalls. The architect’s fees are wasted. The funder loses confidence.
In each case, the cost of commissioning a proper cost plan — typically £1,500 to £8,000 depending on project scale — is a fraction of the cost of the mistake it prevents.
The RapidQS Approach — Fast, Accurate, Built From a Builder’s Perspective
Here’s something most QS firms won’t tell you: the traditional cost planning process is slow, expensive, and designed for large projects with long programmes and deep client pockets.
We come from a builder’s background. We know what it’s like to be on the tools, to manage a site, to deal with a QS report that arrived six weeks late with numbers that bore no relation to what trades were actually quoting. We’ve sat in the same meetings developers sit in when the tender comes back and everyone looks at the QS asking what went wrong.
That experience shapes everything about how RapidQS operates.
We don’t operate like a standard corporate QS firm. We don’t have junior surveyors producing reports that sit in a queue for four weeks. We work at the pace of real development decisions — because we know that by the time a traditional firm delivers their feasibility study, the site has already sold to someone who moved faster.
Our hybrid cost modelling approach:
- Stage 1 Feasibility: Delivered in 24–48 hours for most residential and mixed-use projects. Based on current market benchmarks from live projects we’ve priced, not stale industry databases.
- Stage 2/3 Cost Plans: Produced in 3–5 working days from receipt of drawings. Elemental breakdown with regional adjustment, specification-sensitive rates, and full preliminaries and contingency schedule.
- Stage 4 Full BOQ: 5–10 working days depending on project scale. Full measured quantities, NRM2 structure, live formulas throughout, ready for tender issue.
- Tender Review: We’ll review any tender return against our cost plan and give you a plain-English recommendation within 48 hours.
We work with developers, architects, contractors, and private clients across the UK. Some clients come to us for a single feasibility study. Others work with us through the entire project lifecycle from site appraisal to final account. Both are fine. We don’t push you into services you don’t need.
What we do push is accuracy, speed, and honesty. If your project isn’t viable, we’ll tell you. If your budget is tight, we’ll show you where the risk sits. If you’re about to go to tender on an incomplete drawing package that will generate a dozen variations and a disputed final account, we’ll flag it.
That’s the builder’s background talking. And it’s the difference between a QS report that sits on a shelf and one that actually helps you make better decisions.
Ready to Commission Your Cost Report?
Whether you need a 48-hour feasibility study before a site purchase, a Stage 3 cost plan for your funder, or a full BOQ for tender — RapidQS delivers it fast, accurately, and at a price that makes sense for your project.
Call: +44 7438 628277
Email: david@rapidqs.com
Web: rapidqs.co.uk/contact
RapidQS provides feasibility studies, RIBA-stage cost plans, detailed schedules of costs, and full bills of quantities to developers, architects, and contractors across the UK. We work fast, we work accurately, and we come from a background that means we understand what’s actually happening on your project — not just what the drawings say.
