Voice AI · Real EstateProduction · 6-week build

AI Voice Agents that automated 85% of property inquiry calls — answered instantly, 24/7.

A UK property group was losing qualified buyers and renters to a 4-hour callback window. We shipped a voice agent on Vapi + ElevenLabs + n8n that answers in under a second, qualifies intent in 3 minutes, books viewings in Calendly, and syncs everything to HubSpot — automatically.

PDF · 3 pages · 6-week build

85%

Calls automated

6h → 0s

Answer time

3.8×

Viewings booked

−68%

Cost per lead

The challenge

A 4-hour callback window was handing leads to competitors.

The lettings team received 300+ inbound enquiries per week. After-hours and weekend calls went unanswered until the next working day. Buyers and renters moved on. Hiring a 24/7 call centre was quoted at £320K/year — before a single viewing was booked.

The solution

A voice agent that never sleeps, never misses a call.

We built a branded AI voice agent in ElevenLabs, deployed it on Vapi's phone infrastructure, and orchestrated every downstream action — CRM update, viewing booking, WhatsApp confirmation — through n8n. Complex cases warm-transfer to humans with full transcript context pre-loaded.

Tech stack

What we built it on.

VapiElevenLabsRetell AIn8nGPT-4oHubSpotCalendlyWhatsApp

Voice Platform

Vapi (call infrastructure + WebRTC)
ElevenLabs Turbo v2.5 (voice synthesis)
Retell AI (A/B voice testing)
Deepgram Nova-3 (STT)

Orchestration & AI

n8n workflow automation
OpenAI GPT-4o (reasoning)
Function calling + tool use
Custom intent classification

Knowledge & Context

Property listings API sync
pgvector (semantic search)
Redis (session memory)
Structured FAQ knowledge base

CRM & Bookings

HubSpot CRM sync via n8n
Calendly viewing scheduler
WhatsApp Business follow-up
Twilio SMS fallback

Observability

Vapi call analytics dashboard
n8n execution logs
Sentry error tracking
Custom QA replay tool

Architecture

How the agent flow works.

Step 01

Call Received

Vapi answers within 600ms. ElevenLabs voice greets the caller with the agency's branded persona.

Step 02

Intent Classified

GPT-4o identifies intent from 11 categories: availability, pricing, booking, complaints, and more.

Step 03

Action Triggered

n8n fires the matching workflow: HubSpot lead created, Calendly slot offered, or warm transfer initiated.

Step 04

Follow-Up Sent

WhatsApp confirmation + Calendly invite sent automatically. CRM updated with full call transcript.

Timeline

6 weeks from kickoff to full production traffic.

Week 1
Discovery & Call Audit
Listened to 180+ recorded inquiry calls, mapped 11 intents (availability, pricing, area, booking, complaints), defined success metrics with the lettings team.
Week 2
Voice Persona & n8n Workflow Design
Designed the agent persona and voice in ElevenLabs, sketched all n8n trigger-action flows for CRM sync, booking, and SMS fallback. Validated with stakeholders.
Week 3–4
Vapi Integration + ElevenLabs Tuning
Wired Vapi phone numbers to the GPT-4o reasoning layer. Ran 40+ test calls to tune ElevenLabs voice speed, pause timing, and barge-in sensitivity. Hit sub-600ms latency.
Week 5
n8n Integrations + Shadow Testing
Built n8n workflows: HubSpot lead creation, Calendly booking on intent detection, WhatsApp confirmation, SMS fallback. Ran 900 shadow calls in parallel with human agents.
Week 6
Production Rollout & Optimisation
Phased ramp 20% → 100% traffic. A/B tested two ElevenLabs voices via Retell AI — 'Sophie' outperformed by 18% on CSAT. Handed over QA dashboard and runbook.

Results after 90 days

Hard numbers, not vibes.

85% of inbound property calls fully handled — zero human touch.
Answer time: under 1 second, down from a 4-hour callback window.
3.8× more viewings booked, with a 94% show-up rate.
−68% cost per qualified lead vs. outsourced call centre quote.
CSAT 4.4 / 5 across 2,600 surveyed callers.
18% CSAT lift after A/B testing two ElevenLabs voices via Retell AI.

Deliverables

What shipped.

Production voice agent with 11-intent qualification flow
ElevenLabs voice persona tuned to brand guidelines
n8n automation suite: CRM, bookings, WhatsApp, SMS
Retell AI A/B voice testing harness
QA dashboard with call replay and regression suite
Ops runbook and 30-day support retainer

"We stopped losing leads overnight. The agent books viewings at 2am and our team walks in every morning with a full diary. Best ROI decision we made this year."

Head of Lettings · UK Property Group (NDA)

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