Office conversion feasibility study: secure your decision before capex
1 billion sqm of tertiary stock: the boundaries of your decision
1,200 to 1,800 EUR/sqm committed on an asset manager’s intuition: that is the standard error margin of a conversion launched without a structured feasibility study. With a vacancy rate in the Paris region above 10% since 2023 and the regulatory obligation to reduce the energy consumption of the tertiary building stock by 40% by 2030, the decision between renovation, change of use and divestment can no longer wait. Across the operations we have supported since 2006 through our 11 agencies in France and Spain, a significant share of the tertiary assets we diagnose reveal functional obsolescence or structural under-occupation. In 6 to 8 weeks we deliver a feasibility study that holds up in an investment committee for amounts above 1M EUR: a multi-criteria matrix, 2 to 3 programmatic scenarios costed to within ±15%, a Gantt schedule, and a modelled regulatory energy compliance trajectory. In practical terms, it is a decision-making tool for your investment committee, not an architect’s deliverable. Here is how we frame the three feasibility dimensions, technical, regulatory and economic, and what you gain from it across the decision cycle.
the context
The French tertiary building stock represents around 1 billion sqm. Across this stock, the tertiary decree mandates -40% in energy consumption by 2030, -50% by 2040 and -60% by 2050 compared with a reference year after 2010. At the same time, the vacancy rate in the Paris region has exceeded 10% since 2023.
Your decision plays out across three trajectories with significant differences in market value depending on the path chosen:
| Trajectory | Main tension | Regulatory framework |
|---|---|---|
| Major tertiary renovation | Capex vs ESG yield premium | Articles R4211 to R4217 |
| Residential, hotel or serviced-residence conversion | PLU, regulatory clearance | Change of use, ERP |
| Sale as-is | Discount incurred | Buyer due diligence |
Kytom frames the technical (structure, grids, facades), regulatory (PLU, ERP, accessibility) and economic feasibility. A structured upstream study significantly reduces the budget overruns observed during the construction phase.
Our contrarian reading. Common practice favours residential conversion as soon as tertiary vacancy exceeds 10%. Across the decisions we compare, we document the opposite in a notable proportion of cases: major renovation with ESG repositioning delivers a higher IRR than residential conversion, where the PLU is restrictive or the clearance cost is high. Change of use is not the default option, it is the exception.
your gains
What a quarter saved is worth on a 15M EUR asset
For a 5,000 sqm tertiary asset valued at around 15M EUR, each quarter of delay on the decision costs 75 to 150K EUR in foregone rent or discount incurred (Kytom 2023 calculation, assuming a gross yield of 4.5 to 6%). A Kytom feasibility study priced at 25 to 40K EUR excl. VAT pays for itself in less than one month of a shortened decision cycle.
A dedicated feasibility study significantly improves the accuracy of capex estimates, reduces construction overruns thanks to upstream technical and regulatory framing, and enables you to value the ESG premium between a certified asset and a comparable non-certified asset.
The final deliverable incorporates the modelled regulatory trajectory for reducing tertiary energy consumption, the calculation of the 2030 target consumption against the chosen reference year, and the capex sensitivity across the three scenarios. Your financial analysts have at their disposal a robust, traceable file, ready to be used directly in an investment committee for amounts above 1M EUR.
ESG value creation
LEED v4.1 BD+C adopts ASHRAE 90.1-2016 as the reference standard for energy performance, assessed on cost and GHG emissions. The other certification frameworks are integrated into the scenario according to their feasibility.
For assets targeting ESG value creation, we assess the feasibility of the triptych of certifications used in premium tertiary offices, with an estimate of the incremental capex specific to each scenario.
| Framework | Scope | Indicative additional cost |
|---|---|---|
| International environmental operations certification | Operations, environment | On quotation depending on scope |
| French environmental operations framework | Environmental performance | On quotation depending on scope |
| International well-being standard | Well-being, air quality | On quotation depending on scope |
For each scenario we cost the achievable level and the associated capex. Environmental project management mobilises recognised carbon accounting methodologies and reference technical guides on sustainable building to ensure reliable LCA and carbon footprint, as required by the CSRD reporting of listed property companies.
Our contrarian reading. ESG conventional wisdom pushes towards stacking all three frameworks to maximise the investor storytelling. In practice, pursuing all three certifications simultaneously generates a significant cumulative additional cost for a marginal yield gain that is limited compared with a dual framework combining international environmental operations certification and the French environmental operations framework. We recommend a targeted dual framework, unless there is an explicit investor positioning on the full triptych.
limits
When our 6-8 week feasibility study is not the right tool
Commercial honesty is part of our method. Three cases where we steer towards an alternative approach:
- An asset below 1,500 sqm intended for a straight sale without change of use. The study cost (15 to 25K EUR excl. VAT) then represents more than 1% of the market value, which erodes the ROI of the decision. A 2-week flash audit is enough to decide between renovation and sale.
- A building already under a sale agreement with buyer due diligence underway. Duplicating a feasibility study on the seller side rarely adds value; we recommend a targeted counter-report on the 2 or 3 friction points identified in the buyer’s DD.
- A portfolio below 10,000 sqm managed directly. A 2-week flash audit, at 8 to 12K EUR excl. VAT, is often enough to decide between renovation and sale without mobilising the full multidisciplinary team.
In these three configurations, we propose a streamlined format (flash audit, counter-report, opportunity note) rather than a full feasibility study. The objective remains the same: to give you a robust, traceable deliverable, aligned with your committee’s figures, without wasting your study budget.
Method
- Diagnostic of the existing building
Weeks 1-2. Geometric surveys, structural and services audit, ERP regulatory status and compliance with the applicable requirements R4211 to R4217, reference acoustic measurements and indoor air quality at 5 to 8 points per floor plate. Kytom protocol aligned with the recommendations in force on workplace acoustics. - Programming
Weeks 2-4. Construction of 2 to 3 contrasting use scenarios (flex office, coliving, serviced residence, hotel), floor-area ratios and capacity per scenario, PLU and easement analysis, identification of the regulatory clearances required for a change of use. - Costing
Weeks 4-6. Capex estimate to within ±15%, projected opex over 10 years, Gantt schedule based on 12 weeks per 1,000 sqm tranche. Modelling of the regulatory trajectory for reducing the energy consumption of the tertiary building stock and of the incremental capex linked to the certifications targeted. - Final presentation
Weeks 6-8. Multi-criteria matrix incorporating IRR, NPV, payback, capex sensitivity, compliance with the regulatory obligations to reduce the energy consumption of the tertiary building stock, and the certifications targeted. A robust file for an investment committee for amounts above 1M EUR, traceability, an in-session presentation with the multidisciplinary team mobilised.
Frequently asked questions
Combien coûte une étude de faisabilité reconversion bureaux KYTOM ?
The cost of a conversion feasibility study varies with the asset’s floor area. KYTOM observes a budget of €25–40K excl. VAT for an 850 m² floor plate, and €60–120K excl. VAT for an 18,000 m² complex (2022–2024 portfolio average). This equates to 0.15–0.30% of the asset’s market value and strengthens investment committee decisions ahead of any commitment above €500K.
