Quick Answer
Subcontractors use RTK GNSS receivers to lay out work points, verify installations against design, and document as-built conditions with centimetre accuracy. This replaces traditional methods like string lines and tape measures, reducing rework from misplaced conduits, pipes, or ductwork. A typical RTK setup pays for itself within 2-3 projects through faster layout and fewer correction hours.
Why Subcontractors Need RTK GNSS
Electrical, plumbing, and HVAC subcontractors face constant pressure to install accurately in tight schedules. Traditional layout methods - measuring from walls, pulling string lines, using tape measures - work but are slow and prone to errors. One misplaced conduit run can mean hours of rework, material waste, and coordination headaches with other trades.
RTK GNSS provides centimetre-level positioning anywhere on site, letting you:
- Lay out work points faster - Find design coordinates in seconds, not minutes
- Verify before covering - Confirm installations match plans before concrete pours or drywall
- Document as-builts - Record exact locations for handover documentation
- Avoid clashes - Check your route against other trades' work
Common Subcontractor Use Cases
Electrical Contractors
Layout tasks: Conduit runs, junction box locations, panel positions, cable tray routes
Why RTK helps: Electrical often goes in first or last. You need to coordinate with other trades and hit precise locations for connections. RTK lets you lay out routes in minutes and verify positions before trenching or drilling.
Plumbing Contractors
Layout tasks: Pipe routes, manhole locations, cleanout positions, drainage slopes
Why RTK helps: Gravity drainage requires precise elevation. RTK gives you vertical accuracy (1-2cm) to verify falls and avoid rework. Document as-builts before backfilling.
HVAC Contractors
Layout tasks: Ductwork routes, diffuser positions, equipment pads, penetration points
Why RTK helps: Ductwork competes for space with structure and other services. RTK lets you verify routes avoid clashes and hit architectural positions for grilles and diffusers.
Earthworks Subcontractors
Layout tasks: Foundation levels, grading stakes, excavation limits, compaction testing locations
Why RTK helps: Fast grade checking without setting up levels. Collect as-built surfaces for payment verification. See our drone mapping guide for aerial survey workflows.
RTK vs Traditional Layout Methods
| Method | Accuracy | Speed | Setup Time |
|---|---|---|---|
| Tape measure | ±5-10cm | Slow | None |
| String line | ±2-5cm | Medium | 10-20 min |
| Total station | ±2-5mm | Fast | 15-30 min |
| RTK GNSS | ±1-2cm | Fast | 2-5 min |
RTK advantage: No line-of-sight required. Work around obstacles, other trades, and across the entire site without repositioning. Browse GPS navigation systems for current options.
How RTK Layout Works
1. Load design coordinates - Import points from CAD/BIM into your RTK controller
2. Set up base station - RS4 Pro on tripod, or use NTRIP network corrections
3. Navigate to points - Rover guides you to each design coordinate
4. Stake and verify - Mark points, check positions, move to next
5. Document - Collect as-built points for records
Cost Justification
Typical RTK setup cost: £2,000-3,500 for base + rover kit
How fast it pays back:
- 1 hour saved per day on layout = £50-100/day (depending on crew cost)
- 1 rework avoided = £500-2,000+ in labour and materials
- Break-even: 20-40 project days, or 2-3 typical subcontract packages
For site-wide work, the RX2 network rover offers a lower-cost option if you have reliable mobile signal for NTRIP corrections.
Integration with BIM and CAD
Modern RTK workflows connect directly to project models:
- Import points from Revit, AutoCAD, or Navisworks
- Navigate to 3D coordinates in the field
- Export as-built points back to BIM for handover
- Generate compliance reports automatically
This eliminates manual coordinate transcription errors and keeps field work synchronised with design.
FAQ
Q: Do I need a licence to use RTK on UK construction sites?
A: No licence needed for RTK equipment. If using LoRa radio for base-to-rover link, ensure compliance with Ofcom IR 2030 (usually licence-exempt at 868MHz). See our Emlid Reach guide for licensing details.
Q: Can I use RTK indoors?
A: No - GNSS requires satellite visibility. For indoor work, use total stations or laser Plummet. RTK works for building exteriors, slabs, and outdoor services.
Q: How accurate is RTK for elevation?
A: Typically 1-2cm vertical accuracy. Good enough for drainage falls and level checks, but verify critical elevations with conventional survey methods.
Q: What's the learning curve?
A: Basic operation: 1-2 days training. Full BIM integration: 1-2 weeks. Most subcontractors become productive within the first week.
Last updated: March 2026