Reusing a Three-Year-Old Survey for a Multi-Tenant Re-Let
Northline Property Group manages a 63,000 sq ft, three-floor office building built in 2007. A 2019 Wi-Fi survey PDF shows 22 APs and -65 dBm coverage everywhere. The building is being re-let: floor 2 will house a 180-seat call center using softphones on laptops, floor 3 a medical billing tenant with 60 wireless scanners, and floor 1 will be split into six suites with new drywall and a steel-framed server room. The landlord wants to skip an on-site survey, reuse the 2019 AP layout, and rely on a predictive survey from the 2019 floor plans. The tenant's IT lead insists voice needs -67 dBm and 20% cell overlap and wants a report suitable for an SLA. Construction adds 40 mm metal stud walls and a 3 m-wide freight elevator shaft in the center of floor 1.
1. Explain why the 2019 predictive survey cannot be the basis for the SLA. Give at least four specific risks in this building.
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A predictive survey is a model, not a measurement. It assumes wall attenuation values, AP mounting heights, and antenna patterns that may not match this building, and the 2019 inputs no longer describe the space. Specific risks: (1) floor 1 is being rebuilt with new drywall, a steel-framed server room, and a freight elevator shaft that will shadow cells and change attenuation; (2) the call center's 180 softphone users create uplink capacity and roaming load that a coverage-only model ignores; (3) the 22 APs may have been moved, replaced, or re-cabled since 2019; (4) neighboring-tenant and outside interference has changed, so the 2019 channel plan may now conflict. The -65 dBm claim also cannot be verified without measurements, and voice needs -67 dBm with 20% overlap, which coverage-only prediction rarely proves. Using it as an SLA basis transfers unquantified risk to you.
2. Outline the survey activities and deliverables you would propose, including what must be measured for the call center and the scanner tenant.
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Do a pre-survey walkthrough and spectrum analysis on all three floors, then an AP-on-a-stick survey using the intended AP model and antennas. On floor 2, survey at seated and standing height in the call center layout and measure RSSI, SNR, and co-channel interference; model 180 associated clients and check AP uplink and channel utilization. On floor 3, verify scanner coverage at 1.2 m in the planned rack and desk locations and test roaming between APs. Floor 1 suites need each suite surveyed separately after framing, because the elevator shaft and server room will create dead spots. Deliverables: as-built floor plans with AP locations, RSSI and SNR heat maps, channel and power plan, AP bill of materials with mounting and cabling, PoE budget, spectrum plots, and a signed validation report with pass/fail per area.
3. Construction is still underway. How would you sequence the survey, and what temporary assumptions would you document?
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Sequence: (1) pre-construction meeting and review of as-built drawings; (2) rough-in survey after framing but before drywall to catch the elevator shaft and server-room steel; (3) final AP-on-a-stick after drywall and above-ceiling cabling, before tenants move in; (4) post-move-in validation once furniture and people are present. Document temporary assumptions explicitly: wall attenuation values used before the final survey, AP mounting height, ceiling type, and the assumption that the 2019 cable plant is reusable. Mark the survey report 'interim' and exclude SLA sign-off until final validation. If the landlord insists on a predictive design now, deliver it as a design intent with a stated confidence level, not a coverage guarantee, and put the on-site validation in the contract.