RIBA Cost Plan: What Is It and How Is It Prepared?

A RIBA cost plan is the budget document a quantity surveyor produces and updates alongside the design, tracking a project's likely cost as it moves through the RIBA Plan of Work from an early idea to construction-ready drawings. It isn't one document - it's a series of increasingly detailed cost estimates, each one pinned to a design stage, each one narrowing the gap between what the client hopes the project will cost and what it will actually cost to build.

For anyone starting out in quantity surveying, the RIBA cost plan is one of the first core skills to master. Get it right and you give the design team a budget they can design against with confidence, flag cost risk early enough to do something about it, and hand over a pre-tender estimate that isn't a nasty surprise. Get it wrong - by pricing off an unclear scope, carrying a single vague contingency line, or failing to reconcile against the previous stage - and the project either blows its budget or gets value-engineered to death at the worst possible moment.

This guide walks through what a RIBA cost plan actually is, how it evolves from the Stage 1 order of cost estimate through to the Stage 4 detailed cost plan, the RICS NRM1 elemental structure that gives it consistency, how contingency should shrink as design certainty grows, and the practical steps a QS follows to prepare and update one at each stage.

Whether you're a graduate QS preparing your first cost plan or a commercial manager wanting a refresher before your next design team meeting, by the end of this article you'll understand exactly what's expected of a RIBA cost plan at every stage - and where most cost plans go wrong.

Why the Cost Plan Follows the Design Stages

Cost certainty follows design certainty

You cannot price what hasn't been designed. At Stage 1, a QS might know a client wants a 3,000m2 office building on a given site - nothing more. At Stage 4, the same QS is pricing a fully specified frame, a named cladding system and a coordinated services strategy. The cost plan exists precisely to bridge that gap: it gives the client a defensible budget figure at every point along the way, even though the amount of design information available keeps changing. That is why a single 'cost estimate' produced once at the start of a project is never enough - the RIBA cost plan is a living document, re-measured and re-priced at every stage gateway.

Who prepares and owns the cost plan

On a traditionally procured project, the client's quantity surveyor or cost consultant prepares the cost plan through Stages 1-4, working from the architect's and engineers' evolving drawings. On a design and build project, the contractor's QS typically takes over cost plan development once novation happens, usually around Stage 4. Either way, the cost plan is a collaborative output - the QS cannot build an accurate elemental cost plan without design information from the architect, structural engineer and building services engineer, and the whole design team should be treating the cost plan as the budget they are designing against, not a number handed down from on high.

• Client's QS / cost consultant - prepares and issues the cost plan Stages 0-4 on traditional procurement
• Architect and design team - supply the drawings, areas and specification the cost plan is measured against
• Contractor's QS - takes over cost control once novated on design and build, or prices the tender on traditional routes
• Client - approves the cost plan at each stage gateway and signs off any change in cost limit

How the RIBA Cost Plan Evolves From Stage 1 to Stage 4

Stage 1 - Preparation and Briefing: the order of cost estimate

The first cost figure a QS produces is an order of cost estimate, not yet a formal cost plan. With only a brief, a rough area and maybe a site plan to go on, the QS applies a floor area rate (cost per m2 of gross internal floor area) or a functional unit rate (cost per bed, per pupil place, per parking space) drawn from benchmarked data on comparable projects. This figure carries a wide accuracy range - often quoted as plus or minus 15-20% - and a correspondingly generous contingency, because almost nothing about the design is fixed yet.

Stage 2 - Concept Design: the first formal cost plan

Once the architect produces a concept design - massing, approximate floor areas by use, an outline structural and services strategy - the QS can prepare the first formal elemental cost plan, usually called Cost Plan 1. This is structured against the NRM1 element groups (substructure, superstructure, internal finishes, services and so on) rather than a single blended rate, which lets the QS apply different unit rates to different parts of the building and start to see where the cost is really sitting.

Stage 3 - Spatial Coordination: cost plan 2

By Stage 3, the design team has coordinated the architecture, structure and services into a single set of spatially coordinated drawings, and the QS re-measures and re-prices the cost plan against that coordinated design. Quantities firm up across most elements, provisional sums start to be replaced with measured items, and the accuracy range narrows to something like plus or minus 7-10%.

Stage 4 - Technical Design: the pre-tender cost plan

Stage 4 technical design produces the detail a contractor needs to build from - full specifications, coordinated services drawings, structural calculations. The cost plan at this point (Cost Plan 3, or the pre-tender estimate) is closely aligned to what will actually go out to tender, often supported by a full bill of quantities or a detailed specification. This is the figure the client uses to make the final go/no-go decision before committing to construction, so it needs to be as close to the eventual tender return as the QS can make it.

The NRM1 Elemental Structure Behind Every RIBA Cost Plan

From Stage 2 onward, a RIBA cost plan is built around the RICS New Rules of Measurement 1 (NRM1) - the standard method of quantifying and structuring building costs used across UK construction. Rather than one lump sum, NRM1 breaks the building down into standard element groups, so costs can be compared like-for-like between projects and tracked element by element as the design changes.

• Facilitating works - demolition, site clearance, temporary diversions
• Substructure - foundations, ground floor slab
• Superstructure - frame, upper floors, roof, stairs, external walls, windows, internal walls and doors
• Internal finishes - wall, floor and ceiling finishes
• Fittings, furnishings and equipment
• Services - mechanical, electrical, lifts, public health
• Complete buildings and building units (where relevant, e.g. modular)
• Work to existing buildings (refurbishment projects)
• External works - hard and soft landscaping, drainage, external services
• Main contractor's preliminaries, overheads and profit, plus project/design team fees, risk allowances and inflation, added below the element groups

The elemental structure does two things for the QS. First, it makes benchmarking possible - a cost per m2 for 'services' on this project can be sense-checked against services costs on the last three similar projects, which a single blended rate never allows. Second, it makes the cost plan a genuine design tool: when the structural engineer swaps a steel frame for concrete, the QS can isolate exactly which element moved and by how much, rather than re-estimating the whole building from scratch.

Contingency and Risk: Why the Allowance Shrinks as the Stages Progress

Every RIBA cost plan carries a contingency allowance - money set aside for the things that haven't been designed yet, the risks that haven't been resolved, and the scope that might still change. Crucially, that allowance is not a fixed percentage plucked from habit; it should fall as the stages progress, because the design is becoming more certain and fewer things are still unknown. A Stage 1 order of cost estimate, built on almost no information, might reasonably carry 15-20% contingency. By Stage 4, with a fully coordinated technical design, that figure should have fallen to something closer to 3-5%.

The trap many junior QSs fall into is reducing the contingency percentage to hit a target budget, rather than because the underlying uncertainty has actually gone down. If the design hasn't moved on since the last stage, the contingency shouldn't move down either - doing so just hides risk inside a smaller number instead of removing it. Good practice is to link the contingency allowance directly to a live risk register, so every pound held back corresponds to a specific, named risk that the design team is actively working to resolve or close out.

How a RIBA Cost Plan Is Prepared and Kept Up to Date

Step 1: measure the current design

The QS starts by taking off quantities from the latest drawings issued for that stage - gross internal floor area at Stage 1 and 2, moving to more detailed element-by-element measurement as drawings develop through Stage 3 and 4.

Step 2: apply rates from cost data and benchmarks

Each element is priced using a combination of the QS's own cost database, published cost data (such as BCIS), and rates from recently tendered comparable projects, adjusted for location, market conditions and specification.

Step 3: build up preliminaries, fees, risk and inflation

On top of the measured building works, the QS adds main contractor's preliminaries, overheads and profit, design team fees, a risk/contingency allowance, and an allowance for tender inflation between now and the expected tender date - each shown as a separate, transparent line rather than buried inside a single number.

Step 4: reconcile against the previous cost plan and report

This is the step that separates a good cost plan from a spreadsheet. The QS compares the new total against the last approved cost plan, explains every significant movement - was it a design change, a market shift, a quantity correction, or a genuine cost saving - and reports that reconciliation to the client and design team so everyone understands why the number has moved, not just that it has.

Common Pitfalls When Preparing a RIBA Cost Plan

Most cost plan disputes trace back to a handful of recurring mistakes. Knowing them in advance is the fastest way to avoid repeating them.

• One vague contingency line - lumping design development, risk and scope gaps into a single figure destroys accountability; keep them as separate, named allowances
• Not reconciling against the previous stage - issuing a new total without explaining the movement leaves the client unable to trust the figure
• Measuring off out-of-date drawings - pricing a superseded design produces a cost plan that's wrong before it's even issued
• Ignoring tender price inflation - a cost plan that's accurate today but doesn't account for movement to the tender date will be under budget on day one
• Poor or mismatched benchmark data - comparing a high-spec residential scheme against a warehouse cost per m2 rate produces a meaningless number
• Reducing contingency to hit a target budget rather than because uncertainty has genuinely reduced
• Not aligning the cost plan structure to NRM1 - a bespoke, one-off structure can't be benchmarked against past projects or industry cost data

Frequently Asked Questions

What is the difference between an order of cost estimate and a cost plan?

An order of cost estimate is the early, Stage 1 figure produced from very limited design information, usually using a floor area or functional unit rate. A cost plan is the more detailed, elementally structured document produced from Stage 2 onward, built up against the RICS NRM1 element groups as the design matures.

How many cost plans are produced during a RIBA project?

Typically three formal cost plans are produced - Cost Plan 1 at Stage 2 (Concept Design), Cost Plan 2 at Stage 3 (Spatial Coordination), and Cost Plan 3, or the pre-tender estimate, at Stage 4 (Technical Design) - preceded by an order of cost estimate at Stage 1.

What is NRM1 and why does it matter for a RIBA cost plan?

NRM1 is the RICS New Rules of Measurement standard for order of cost estimating and elemental cost planning. It gives every cost plan a consistent element-by-element structure, which allows QSs to benchmark costs against comparable projects and track exactly where cost is moving as the design develops.

How much contingency should be included in a Stage 2 cost plan?

There's no fixed rule, but a Stage 2 cost plan commonly carries a contingency in the region of 10-15%, falling from a wider Stage 1 allowance and reducing further to around 3-5% by Stage 4 as design uncertainty is resolved. The right figure always depends on project complexity and site risk.

Who is responsible for preparing the RIBA cost plan?

On traditional procurement, the client's quantity surveyor or cost consultant prepares and updates the cost plan through Stages 1-4. On design and build projects, responsibility typically transfers to the contractor's QS once the design team is novated, usually around Stage 4.

What happens to the cost plan after RIBA Stage 4?

Once the project goes to tender and a contractor is appointed, the cost plan is effectively superseded by the contract sum analysis or priced bill of quantities. From Stage 5 onward, cost control continues through interim valuations, cost value reconciliations and, ultimately, the final account.

Can a cost plan and a budget be the same thing?

Not quite. A budget is usually the fixed figure the client has available to spend, set early and often held constant. The cost plan is the QS's running estimate of what the design will actually cost - the two are compared at every stage, and any gap between them has to be actively managed through value engineering, scope changes or a revised budget.

Final Thoughts

A RIBA cost plan is never really 'finished' until the final account is agreed - it's a discipline of continuous re-measurement, re-pricing and reconciliation that runs alongside the design from Stage 1 to Stage 4 and beyond. The QSs who do this well aren't the ones with the most sophisticated spreadsheet; they're the ones who keep the elemental structure consistent, keep contingency honestly linked to real risk, and can explain exactly why the number has moved every time it does.

Master that discipline early in your career and it pays off well beyond cost planning itself - it's the same reconciliation mindset that underpins cost value reconciliations, final accounts and every other budget conversation you'll have as a QS.

Want the full picture? Want to go deeper on cost planning?

Read our companion guides on Construction Cost Planning: A Complete QS Guide for the full elemental worked example, Construction Cost Estimating: A Beginner's Step-by-Step Guide for how early estimates are built up, and What Is a Risk Register? A Construction QS Guide to see how contingency should be linked to a live risk register rather than a single guessed percentage.