The verdict in three sentences
A low-carbon website built to the French RGESN framework and the W3C Web Sustainability Guidelines costs about 10 to 20% more in 2026 than a standard corporate site priced at €15,000 to €30,000 ex VAT, an extra €1,500 to €6,000. That premium buys pages under 500 KB, an EcoIndex A or B score, load times cut in half and a footprint close to 1.2 g CO2e per page view versus 2.5 g for a heavy site. For a mid-sized Dutch company documenting its digital footprint in a sustainability report, it is also quantified, auditable evidence, which broad pledges never provide.
Standard site or lean site: what actually changes
The RGESN (general ecodesign framework for digital services), published by French regulators Arcep, Arcom and ADEME in its 2024 version, contains 78 criteria and is increasingly used across Europe alongside the W3C guidelines. It sets no maximum page weight, but its criteria naturally lead to lighter pages, fewer third-party scripts and right-sized hosting.
| Indicator | Standard corporate site | Lean RGESN site |
|---|---|---|
| Average page weight | 2 to 3 MB | 300 to 500 KB |
| Number of requests | 70 to 120 | 20 to 40 |
| EcoIndex score | D or E | A or B |
| Emissions per page view (EcoIndex) | 2.3 to 2.7 g CO2e | 1.1 to 1.4 g CO2e |
| Largest Contentful Paint (mobile 4G) | 3 to 4.5 s | 1.2 to 2 s |
| Third-party scripts (trackers, widgets) | 8 to 15 | 0 to 3 |
| Build budget | €15,000 to €30,000 ex VAT | €16,500 to €36,000 ex VAT |
Lean does not mean austere. The choices are AVIF or WebP images sized for display, system fonts or a single self-hosted font, click-to-play video instead of autoplay, and cookieless analytics.
Where the 10 to 20% premium goes
The premium is not only technical. It splits between more demanding upfront design and the evidence a sustainability report needs.
| Item | Scope | Estimated premium |
|---|---|---|
| Sustainability scoping | Review of useful features, removal of dead pages, weight budget per template | €800 to €1,500 ex VAT |
| Light UX design | Short journeys, reusable components, no carousels | €500 to €1,200 ex VAT |
| Optimised media | AVIF/WebP conversion, responsive sizes, on-demand video | €400 to €1,000 ex VAT |
| Lean front-end build | Minimal JavaScript, static rendering, long caching | €0 to €1,200 ex VAT |
| Green hosting | Dutch or EU data centre on renewable power, PUE below 1.4 | €0 to €600 ex VAT a year |
| RGESN audit and statement | 78-criterion checklist, EcoIndex measurements, published statement | €1,200 to €2,500 ex VAT |
Part of the premium pays back quickly: a lighter site uses less bandwidth, needs a smaller hosting plan (often 20 to 40% cheaper) and ranks better thanks to Core Web Vitals. Companies that rebuilt along these lines often see mobile bounce rates fall by 10 to 25%.
Using the metrics in sustainability reporting
The EU Omnibus package adopted in 2025 delayed and narrowed CSRD scope, so a 300-employee company may no longer report under it directly. Its large customers and banks still ask for comparable data, often using the voluntary VSME standard. A lean site delivers five usable data points.
| Element | Reportable indicator | Measurement frequency |
|---|---|---|
| Ecodesign statement | Number of RGESN criteria met out of 78 | Annual |
| Environmental score | Average EcoIndex of the 20 most viewed pages | Quarterly |
| Carbon footprint | g CO2e per page view and annual total | Annual |
| Hosting | Share of renewable energy, data centre PUE | Annual |
| Performance | Median mobile LCP | Monthly |
These figures are methodological estimates and should be presented as such. Their value lies in the trend: showing a 50% drop in footprint per page between the old and new site is a verifiable commitment.
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Mini case study
Sanne, sustainability lead at a 300-employee industrial company near Amsterdam, is overseeing a 60-page rebuild priced at €24,000 ex VAT. The low-carbon option adds 15%, or €3,600 ex VAT. The site gets 40,000 visits a month at 3 pages per visit, so 1,440,000 page views a year. Going from 2.5 g to 1.2 g CO2e per page saves 1.3 g × 1,440,000 = 1.87 tonnes of CO2e a year. Hosting drops from €2,400 to €1,600 a year, already recovering €800 of the premium annually, and mobile LCP falls from 3.8 s to 1.6 s.
FAQ
Is the RGESN mandatory for a private company?
No, it remains voluntary for companies in 2026. Yet more and more private tenders score sustainability at 5 to 10% of the total, and the RGESN gives you a recognised checklist to answer them.
Can a low-carbon site still have animations?
Yes, in moderation: light CSS transitions weigh a few KB, whereas an autoplay background video adds 3 to 8 MB per page. A weight budget per template, often 500 KB, settles the trade-offs.
How do I measure my current site's footprint?
The free EcoIndex tool analyses a page in seconds and returns a grade from A to G with a g CO2e estimate. Measure your 20 most visited pages to get a representative average.
Do we need to change hosting provider?
Not always, but require an EU data centre running on renewable power with a PUE below 1.4. Several Amsterdam-region providers meet this for sites under 100,000 visits a month at modest cost.
How long does a low-carbon site take?
Allow 8 to 12 weeks, 1 to 2 weeks more than a standard site for scoping and audit. The ecodesign statement is published within a month of launch.
Let's scope your project. We price your low-carbon rebuild with a weight budget per page, an RGESN audit and before-and-after EcoIndex measurements, for €16,500 to €36,000 delivered in 8 to 12 weeks. 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.
