The verdict in three sentences
If your foundation is sound (up-to-date CMS, clean code, decent SEO), a partial rebuild at 8,000-15,000 GBP is enough. If technical debt exceeds 40%, the CMS is obsolete, or SEO is already slipping, a ground-up build at 20,000-35,000 GBP pays off better over 3 years. Either way, a botched migration costs 15 to 30% of traffic: that is the real hidden cost to weigh.
The costed decision tree (London, 2026)
Ask these questions in order. Each "no" tips you toward a ground-up build.
| Question | Partial rebuild | Ground-up build |
|---|---|---|
| CMS still maintained? | Yes | No |
| Technical debt < 40%? | Yes | No (> 40%) |
| Current SEO healthy? | Yes | No (already slipping) |
| Design < 4 years old? | Yes | No |
| Functional needs stable? | Yes | No (new modules) |
Cost ranges by scenario
| Scenario | Scope | GBP cost | Timeline |
|---|---|---|---|
| Refresh | Design + content, same core | 8,000 - 11,000 | 2-4 wk |
| Partial rebuild | UX + design + SEO, CMS kept | 11,000 - 15,000 | 4-6 wk |
| Ground-up | New core, new IA | 20,000 - 28,000 | 6-10 wk |
| Premium build | + integrations, multilingual | 28,000 - 35,000 | 10-14 wk |
The cost of SEO risk (often forgotten)
A poorly prepared migration can cost more than the project itself. A 15 to 30% drop in organic traffic for 2 to 4 months means, for a lead-generating B2B site, dozens of lost enquiries. The safeguards: an exhaustive 301 redirect plan, retention of high-traffic URLs, before/after crawls, and 90-day Search Console monitoring. Budget 1,500-3,000 GBP for serious SEO migration support: it is insurance, not an option.
Mini case study
James, MD of a B2B services firm in London, is torn. His site is 5 years old, runs on an unmaintained CMS, has roughly 55% technical debt and SEO down for 18 months. The tree clearly points to a ground-up build. Quote: 24,000 GBP + 2,000 GBP for SEO migration support. Without that line, a 25% traffic drop (about 30 leads/quarter) would cost far more than 2,000 GBP in lost margin. He approves the ground-up build with secured migration: ROI reached by the second quarter thanks to preserved traffic and new conversion modules.
FAQ
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When should I rebuild rather than start over?
When the foundation is sound: maintained CMS, technical debt under 40%, healthy SEO and a design under 4 years old. A partial rebuild at 8,000-15,000 GBP then suffices.
What is the tipping point toward a ground-up build?
Technical debt above 40%, an obsolete CMS or already-slipping SEO. Beyond that, patching costs more over 3 years than starting on a clean core.
Does a rebuild lose SEO traffic?
Botched, yes: -15 to -30% for 2 to 4 months. Handled well (301 redirects, retained key URLs, 90-day monitoring), the impact is minimal or even positive.
How much for a ground-up build in London?
Between 20,000 and 35,000 GBP depending on integrations, multilingual scope and SEO depth. Expect 6 to 14 weeks.
Should SEO migration be budgeted separately?
Yes: 1,500-3,000 GBP for a redirect plan, before/after crawls and Search Console monitoring. That is what protects your existing traffic.
Let's scope your project. Send us your site's age, CMS and traffic volumes: we assess technical debt and SEO risk, then quote a rebuild or a ground-up build. Detailed quote within 48 h. WhatsApp +221 77 596 93 33.
Mohamed Bah
Fondateur, Kolonell
Passionate about digital and entrepreneurship in Africa, Mohamed has been helping Sénégalese businesses with their digital transformation since 2020. Founder of Kolonell, he believes every SME deserves a professional and accessible online présence.
