Smart home without a building site:
what you can automate in a finished apartment.
Laurențiu Villa · partial retrofit · KNX + Zigbee
The number one question when people call us about an apartment they already live in: can I have a smart home without tearing down walls?
Short answer: yes, for most of the things you want to do. Long answer: with compromises worth understanding before you buy the first sensor.
In the last five years we have delivered 30+ retrofit projects — apartments the clients had already moved into, villas bought finished, holiday homes where a new building site is no longer an option. Below is what we learned: what you can do without chasing walls, what you cannot, what it realistically costs, and the five mistakes that show up every time people try it on their own.
What a smart home retrofit actually means.
Retrofit = adding a smart home system to a house that already exists, without changing the main electrical structure. As opposed to a “greenfield” installation (construction stage), where you pull KNX cables through open walls and have complete freedom.
In a retrofit you work with three constraints:
- Closed walls — you cannot pull new cable without chasing
- Existing electrical circuit — the switches and sockets are where they are, not where you would want them
- Fixed HVAC — if you have a boiler with a single thermostat, you cannot zone easily
The solution: wireless protocols. Zigbee, KNX RF, sometimes Wi-Fi (with reservations). You replace components; you do not modify the structure.
What you can do without a building site.
With Zigbee plus a local hub (Hue Bridge, Aqara M2, Home Assistant Yellow), a complete retrofit of a 2-3 room apartment takes 2-4 working days. This is what normally goes in:
Lighting
You swap the switches for Zigbee ones (Aqara H1, Sonoff ZBMINI), keep the existing bulbs or move to Hue / Trådfri for dimming. Scenes: Cinema, Dinner, Wake up — all possible.
Thermostat
You replace the mechanical thermostat with a Zigbee one (Aqara, Sonoff, Heatit). Weekly schedule, presence-based scenes. For modern boilers with OpenTherm, real modulation.
Security
Magnetic contacts on windows and doors, motion sensors, smoke, flood and gas sensors. All battery-powered (2-3 year life), Zigbee communication. Push notification on an unexpected opening.
Blinds / curtains
Somfy Tahoma motors (RTS or IO) integrated through a Zigbee gateway. For existing blinds with RF motors: a universal remote plus Zigbee modules.
Multi-room audio
Sonos or Bluesound — native Wi-Fi, a mature ecosystem, scene control. Works without new cables in the walls, only the existing sockets. Add speakers as you need them.
Air quality
CO₂, VOC, PM2.5 and humidity sensors (Aqara TVOC, IKEA Vindstyrka). Automatic trigger for ventilation, push alert when the air gets bad. All on batteries or USB.
What you cannot do — or only with compromises.
Real zoned climate
If the boiler has a single thermostat and the heating installation is simple (radiators on a single flow), you cannot zone the climate without a thermostatic head on every radiator. With Zigbee thermostatic valves (Aqara E1, Heatit Z-TRM) it can be done, but it is half a solution.
Audio built into the ceiling
Ceiling speakers need new cabling. The retrofit alternative: Sonos Era 100 / Bluesound Pulse — visible speakers, but with flexible placement. Or a Sonos Beam on the TV for the living room.
More than 50-80 devices
A Zigbee mesh loses reliability beyond 50-80 nodes. For large systems (a complete villa with 100+ devices), wired KNX is the only honest option. Large-scale retrofit = building site.
“Professional” quality of the switchgear
The available Zigbee switches (Aqara, Sonoff) are decent, but they do not compare with a Gewiss Chorus, a Schneider Wiser or a BTicino Living Now. For a home where the finishes matter, it is a real aesthetic limitation.
What it costs, realistically.
The figures below are with a full team (consultation, purchasing, installation, hub configuration, scenes). If you do it yourself, subtract about 40% — but that saves you the hours of configuration and the debugging when three Zigbee devices stop responding.
Five mistakes that show up every time.
Bought five different brands, ended up with five apps
Trådfri for lighting, Tuya for plugs, Sonoff for the thermostat. Six months later nobody uses anything. Solution: choose a single protocol (Zigbee) and a single local hub (Aqara M2 or Home Assistant).
Wi-Fi smart for everything
Wi-Fi has a device limit (about 50 per consumer access point). At 30+ smart devices it starts dropping out. Solution: Zigbee for everything that does not need bandwidth (lights, sensors, thermostat), Wi-Fi only for audio and video.
No scene plan — just isolated gadgets
You buy three sensors, two smart plugs, a thermostat and… nothing talks to anything. Solution: before buying, write down the scenes (Away, Home, Cinema, Night) and only then choose the devices that support them.
Cloud-only hub (Tuya, no-name Chinese brand)
Your system depends on a server in Shenzhen. It goes down, a bad update arrives, GDPR is at their discretion. Solution: a local hub (Aqara M2/M3, Hue Bridge, Home Assistant). Cloud only for remote access, never for basic operation.
Wi-Fi thermostats on HVAC that cannot support them
Older boilers (on a simple relay, no OpenTherm) cannot modulate or do real zone control. You put a Nest on them and… you are left with an expensive on/off thermostat. Solution: check which protocol the boiler speaks (OpenTherm, eBus, an external modulator) before buying a thermostat.
Retrofit is an honest option — but not for every project.
For a lived-in apartment where you want concrete automation and a single app, a retrofit with Zigbee and a local hub is the best choice. The minimum working budget starts at €3,500; for a system that genuinely helps you every day, €5,500–€8,500 for a complete apartment.
For a villa with 100+ devices or premium finishes, retrofit has real limits. If your project is still under construction or a major renovation is coming, choose wired KNX from the first drawing — it costs more up front, but it spares you ten years of tinkering with wireless meshes.
More context in the complete home automation guide (Romanian), the technical KNX vs Zigbee vs Wi-Fi comparison, or detailed pricing.
Questions we get about retrofits.
Can I make a finished apartment smart without breaking walls?
Yes. For finished apartments we use Zigbee — a wireless protocol with its own mesh, independent of your everyday Wi-Fi. You swap the switches for smart ones, add a smart thermostat, install motion and CO₂ sensors — all without major chasing. The work takes 2-4 days.
How much does a smart home retrofit cost?
The minimum budget for a meaningful retrofit starts at €3,500. For a 2-3 room apartment with lights, climate, a thermostat and basic security: €4,500–6,500. For a villa with a full retrofit (audio, motorised blinds, irrigation): €8,000–15,000.
Zigbee vs KNX wireless — which is better for a retrofit?
Zigbee is the most mature retrofit protocol: a large ecosystem (Aqara, Philips Hue, IKEA, Sonoff), good prices, a stable mesh. KNX RF (wireless) is more expensive and has fewer devices available, but it integrates perfectly with an existing wired KNX system. For a pure retrofit, Zigbee. For a retrofit in a house that already has partial KNX, KNX RF.
Does it work without internet?
With Zigbee implemented correctly — yes. The hub runs locally; scenes and buttons work without the cloud. Only remote access (from your phone outside the house) needs internet. Avoid Tuya / cloud-only products — those go down together with the connection.
Let's talk about what would fit.
15 minutes on the phone, no sales agenda. We tell you honestly whether a retrofit makes sense for your project and what budget to plan. English spoken.