Integrated BET design office: 5 technical packages for your offices

Our integrated BET covers five structuring packages for the tertiary sector, addressed from the schematic design (APS) stage rather than during the EXE phase after contracts are awarded. It is this upstream sequencing that explains most of the works savings observed on our completed missions.

• Acoustics: targets of 35 to 45 dB(A) depending on zones, treatment of airborne and impact noise, compliance with the requirements applicable to sound levels in offices.
• HVAC: heating, ventilation, air conditioning, air renewal of at least 25 m³/h per occupant (Labour Code, article R.4222-6), thermal assessment compliant with the environmental regulation in force for the tertiary sector.
• Lighting: 300 to 500 lux depending on use, DALI dimming, integration of solar gains.
• High/low voltage: NF C 15-100 compliance, category 6A pre-cabling, VDI cabinets sized for 1 workstation per 8 sqm at the target IT density.
• Structure: Eurocode verification, admissible loads of 250 to 500 kg/sqm, localised reinforcements.

For operations larger than 2000 sqm, we additionally activate the fire safety packages (SSI categories A to E), smoke extraction and special fluids. MEP coordination beneath the technical raised floor (height of 100 to 300 mm) remains a critical engineering point: four parallel ducts coexist (air, high-voltage electrical, VDI, condensates) and require millimetre-precise layout from the APS stage.

The benefit of an integrated BET is not primarily technical, it is financial and asset-related. Three accounting perspectives apply to the tertiary decision-maker.

Project cash flow. A fragmented study extends the APS-DCE phase by several weeks, delaying delivery and the leasing of the asset by the same amount. For an asset leased at €280/sqm/year, an eight-week delay on 1500 sqm represents €64,600 of unearned rent, excluding lease penalties. The additional cost of an integrated BET is recouped within the first weeks gained.

Operating OPEX. The 65 kWhPE/sqm/year measured post-delivery across our portfolio, compared with a benchmark of 110 kWhPE/sqm/year in the office segment, translate into energy OPEX divided by 1.7. For a 2000 sqm asset at the average 2024 tertiary energy cost, the difference represents €18,000 to €22,000 of OPEX avoided per year, which can be factored into the rental value calculation.

Regulatory compliance. The unified digital DOE secures your annual declarations and your consumption reduction trajectory to 2030. Property management teams cite this point as an operational benefit for maintenance and for handover when an asset manager changes.

Avoided site reworks. The upstream trade-offs across the five packages significantly reduce the site-rework budget line, historically one of the most volatile in tertiary fit-out projects.

Our measured feedback on completed operations quantifies the impact of an integrated BET across three structuring areas: control of works costs, reduction of study duration, and improvement of post-delivery energy performance.

Acoustic comfort consistently emerges as a benefit perceived by occupants in the feedback we collect after delivery. The targeted environmental certifications are achieved on the relevant operations, with the HQE certification offering 3 performance levels per criterion (Base, High Performance, Very High Performance), and a study cost increase that is generally limited within the BET budget.

Our 12-week calibration assumes a tertiary project between 500 and 2500 sqm with no heavy structural constraint or heritage interface. Two cases fall outside this framework and call for a different approach.

Below 300 sqm, the five-package integrated BET is oversized: a simplified technical AMO over 4 to 6 weeks is sufficient, the fixed study cost (around 8% excl. tax) becoming disproportionate relative to the works budget. We then redirect to our lighter advisory offer.

Above 5000 sqm or in the case of creating openings, underpinning, heavy refurbishment or an ABF interface, the sequence must be extended to 16-20 weeks with a level 1 SPS coordinator, otherwise the APD risks being incomplete and the DCE reworks costly.

Four points also frame our scope and must be contractualised upstream. The regulatory technical inspection (L, SEI or PS missions required above 28 metres in height or in ERP) must be entrusted to an approved inspection office (Apave, Bureau Veritas, Socotec, Qualiconsult) that holds the ten-year civil liability on technical opinions. The SPS missions, the ABF opinion in heritage areas and the pre-works asbestos diagnosis also fall to dedicated providers that we coordinate without substituting for them.

1. Existing condition diagnosis
   Over two weeks, our engineers carry out on-site acoustic measurements with a precision sound level meter (class 1), infrared thermography of the facades, illuminance measurements and an audit of the main low-voltage distribution board. Deliverable: a costed diagnosis report and a map of critical points.
2. Technical programming
   Weeks 3-4, we set the quantified targets per package (35 dB(A) for individual offices, 300 lux for workstations, 24°C summer setpoint) and resolve the structural trade-offs with a validated Eurocode calculation note.
3. Coordinated APS
   Weeks 5-7, we produce the LOD 300 BIM model bringing together the five packages and a first cost estimate accurate to plus or minus 10% (measured across 37 Kytom projects 2023-2024 vs final market price).
4. APD and DCE
   Weeks 8-11, we deliver the CCTP per package, structural reservation plans, HVAC schematics, NF C 15-100 single-line diagrams, a detailed quantity schedule and graphical documents at 1/50 scale ready for tender.
5. Bid analysis
   Week 12, we orchestrate the contract finalisation and the comparative table of the consulted companies. Our 1442 engineers then proceed to the visa and DET mission, with a weekly visit to the site.