The two approaches at a glance
In short: Brownfield retains the existing system landscape and migrates it technically to S/4HANA. Greenfield archives all legacy systems and reimplements S/4HANA new — with the chance of process redesign, but at higher risk and longer timelines.
The Brownfield approach means converting your existing SAP system landscape (ERP, ALM, custom developments) step by step onto S/4HANA. Data structures are preserved, customisings are ported, and integration points are retained. According to SAP Official Documentation, Brownfield is the standard choice for organisations with significant customisings and critical integration points. In our experience: that is the majority of DACH SMEs.
The Greenfield approach means: legacy systems are archived. S/4HANA is implemented "on a green field" — with contemporary process design, modern best practices, and a minimal technical-debt footprint. According to LeanIX Technology Transformation Wiki, a pure Greenfield implementation takes 12–24 months and requires intensive change-management resources.
The decisive differences: timeline, risk profile, change effort, process-redesign opportunity, and cost envelope.
When the Brownfield approach is the right choice
In short: Brownfield makes sense when you have a working legacy system, stable business processes, high data quality, and constrained budgets — or when regulatory requirements (GoBD, NIS-2) demand rapid compliance.
1. High customising depth and critical integration points. A mid-sized mechanical engineering company with 450 employees in Baden-Württemberg had over 200 ABAP programs, 85 interfaces to production control, and 120 table extensions. A pure Greenfield approach would have meant 18 months of implementation plus 9 months rebuilding the custom logic — a massive disruption to operations. Brownfield: 8 months of conversion, custom programs ported, integration points kept stable. In our experience, Brownfield here is not just cheaper — the risk is calculable.
2. Tight compliance timelines (GoBD, NIS-2). The SAP documentation lists this explicitly as a Brownfield indicator: if your business is subject to GoBD, NIS-2, or Supply Chain Act reporting requirements, you cannot be offline for 12+ months. Brownfield preserves audit trails and revision logic from the legacy system, securing compliance continuity.
3. Stable, proven business processes. A Swiss wholesaler with 280 employees has been running on a highly optimised process landscape for 12 years — Order-to-Cash and Procure-to-Pay are well established. A Greenfield path would have meant process standardisation per SAP Best Practices — which were 15% less efficient than the existing workflows. Brownfield preserved the process-level competitive advantage.
4. Constrained budgets / TCO pressure. With Brownfield, 85–95% of customisings are typically retained. Greenfield rebuilds almost everything — more development, more testing, higher personnel costs over a longer timeline. In a project with a sanitary-products manufacturer (190 employees, eastern Germany), the Brownfield route saved €320,000 in development costs.
5. High data quality in legacy systems. If your master data is clean, your master data management works, and your historical transaction data is fully archivable, Brownfield is a clear plus. That reduces data-migration risk by 60–70%.
When the Greenfield approach is the right choice
In short: Greenfield pays off when the legacy systems are obsolete (10+ years), the customising load is technically not portable, or when a radical process redesign is strategically necessary.
1. Obsolete legacy systems with minimal maintenance. An electronic-components manufacturer (210 employees, Bavaria) was running SAP R/3 4.6 at EOL status. The system foundation was so fragile that any migration would have required a rebuild. Greenfield here was not only sensible — it was the only safe option.
2. Technically non-portable customisations. If your custom programs rely on obsolete ABAP language features or hacked SAP internals, Greenfield pays off. The technical debt is greater than the cost of a rebuild.
3. Strategic process redesign plus digitalisation. A mid-market company simultaneously launching an omnichannel strategy or building IoT integration into its production control benefits from Greenfield. New processes, new system, no legacy ballast. These companies usually cannot stretch to a parallel "Brownfield + redesign" model.
4. Cloud-first strategy with RISE with SAP. In our experience, Greenfield is more attractive in RISE migration decisions, because SAP RISE has a different licensing model and SLA structure. A pure Brownfield conversion into the cloud can produce hidden infrastructure-migration costs.
5. Multi-site consolidation. A Swiss machinery manufacturer with production sites in Germany, Austria, and Switzerland was running three separate ERP systems. Greenfield allowed for a single, cross-border system landscape — with unified processes, a single data foundation, and a single control environment.
Practical example: a Brownfield decision from 1,200+ projects
In short: A mid-sized tool manufacturer (380 employees, southern Baden) made the Brownfield choice based on three factors: high customising depth, critical Just-in-Time integration points, and GoBD compliance. Result: 7 months of conversion, €520k budget, no compliance regressions.
The company was running SAP ERP 6.0 with 78 ABAP customisings, 42 interfaces to production-planning systems, and a JiT logic that accounted for 25% of margin quality. The first consulting round would have pushed Greenfield — "newer, better, cleaner." But the TCO calculation showed clearly that rebuilding those custom integration points would take 14–16 months. At the same time, GoBD compliance was non-negotiable.
Brownfield decision: The application landscape was technically converted to S/4HANA. The 78 customisings were ported into the new codebase, the 42 interfaces remained functional, and GoBD audit trails were preserved through the cutover. Result: seven months to production go-live, €520k total budget (versus an estimated €680k for Greenfield plus 14 months), no compliance rework.
That is the core of our experience: Brownfield is not "cheaper and old-fashioned". Brownfield is risk-calculable — when the right diagnosis is made.
Decision criteria checklist
Use these 14 yes/no questions to triage your profile quickly. Every "yes" on the Brownfield side increases Brownfield suitability. Every "yes" on the Greenfield side increases Greenfield suitability.
Brownfield indicators:
- Do you have more than 80 SAP customisings (ABAP, extensions, BAdIs)?
- Are more than 30% of your interfaces critical to operational processes?
- Are you subject to GoBD, NIS-2, or Supply Chain Act compliance obligations?
- Is data quality in the main system above 90% (no major duplicates or consistency gaps)?
- Do you have a dedicated SAP development team for custom maintenance?
- Are your business processes demonstrably more efficient than the SAP standard?
- Has your system run stably without critical basis updates for more than 12 months?
Greenfield indicators:
- Is your SAP baseline older than 10 years (EOL or near EOL)?
- Are you planning a parallel strategic digitalisation initiative (omnichannel, IoT, platform)?
- Are more than 50% of your customisings undocumented or built on hacked APIs?
- Are you planning to migrate to RISE with SAP or a multi-cloud strategy?
- Are you planning site consolidation (merging multiple ERP islands into one)?
- Is current data quality below 70% (massive duplicates, orphaned master data)?
- Do you have a digitalisation budget exceeding 30% above the ERP conversion?
Next steps
The decision between Brownfield and Greenfield is too often treated as a cost-optimisation question. In reality, it is a strategic and regulatory architecture question that brings together your technical debt, your compliance obligations, and your digitalisation goals. Our recommendation: organise a multi-day discovery workshop with your CTO/Head of IT, CFO, Compliance Officer, and Head of Operations. Use the checklist above as the framework. Validate your technical debt with a targeted code audit of the top-20 customisings. Calculate TCO for both scenarios over five years — including infrastructure, licences, and personnel. The right decision is not made by benchmarks. It is made through a complete, DACH-SME-specific diagnosis.
