Choose the Model Before the Hardware
| Setup | Best For | Pros | Cons |
|---|---|---|---|
| Separate ISP account | Rental ADU, independent occupant | Clean billing, full privacy, no shared support burden | Higher monthly cost; ISP availability at ADU address may be limited |
| Wired Ethernet extension | Family ADU or same-owner use, <100m run | Best performance; full speed; no interference | Requires conduit or cable path between buildings; electrical isolation needed |
| Fiber extension | Any detached ADU; best for electrical isolation | Full performance; safe cross-building run; immune to ground loops | More expensive than copper; requires media converter at each end |
| MoCA over existing coax | ADU or garage with existing coax run from main house | Uses existing coax; 1–2.5 Gbps throughput | Requires coax to already exist; both ends need MoCA adapters |
| Point-to-point wireless bridge | Detached ADU with outdoor line of sight | No cable required; 100–300 Mbps typical throughput | Requires outdoor mounting, alignment, weatherproofing; affected by trees/obstructions |
| Mesh node / Wi-Fi extension | ADU attached or very close (<15m) to main house | Simple setup; no cable | Variable throughput; privacy limitations; fails through concrete/metal walls |
Running Cable Between Buildings
If you are running new cable between the main house and a detached ADU, follow these rules:
- Never run bare copper Ethernet between separate buildings. Different buildings can have different ground potentials, and a lightning strike or power fault can damage equipment or create a shock hazard. Use fiber optic cable (electrically non-conductive) for any inter-building run.
- Fiber media converters at each end convert the fiber to standard Ethernet. A pair of converters costs $30–80 and handles the electrical isolation completely.
- Underground conduit protects cable from damage, UV, and pests. Use schedule 40 PVC for direct burial and run a pull string for future upgrades.
- Burial depth: check local code — typically 6–12 inches for conduit, 24 inches for direct-buried cable. Most municipalities require conduit.
- Max Ethernet run is 100m (328 ft). For longer runs, use fiber and media converters.
MoCA: Using Existing Coax
If a coax cable already runs between the main house and the ADU (from a former cable TV install), MoCA adapters can convert it to a network link without any new cable:
- MoCA 2.5 adapters provide up to 2.5 Gbps throughput and cost $60–100 per pair
- Install one adapter at the router in the main house, one in the ADU, and connect both to the existing coax
- Works well when the coax run is clean and not split through too many splitters
- Install a POE (Point of Entry) filter on the coax where it enters the main house to prevent signal from leaking to neighbors
Point-to-Point Wireless Bridge
When running cable is impractical and the ADU has line of sight to the main house, an outdoor wireless bridge provides reliable performance:
- Units like Ubiquiti NanoStation or TP-Link CPE can deliver 100–300 Mbps across 30–100m outdoor distances
- Mount one unit on the main house and one on the ADU; aim them at each other and align using the unit's signal strength indicator
- Both units connect via Ethernet to routers or switches inside each building
- Dense vegetation between the buildings degrades performance significantly — trees absorb 2.4/5 GHz signals
- These units are weatherproof but should be mounted under eaves or with the cable entry sealed
Network Segmentation for Tenant Privacy
If sharing a connection between the main house and an ADU, always isolate the networks:
- Put the ADU on a separate VLAN or guest network so ADU devices cannot see main-house printers, NAS, cameras, or computers
- Use a router that supports VLAN tagging or at minimum a guest network with client isolation enabled
- Set a separate Wi-Fi SSID and password for the ADU — never give tenants the main house Wi-Fi credentials
- Size upload capacity for simultaneous video calls: two people in the main house and one in the ADU all on calls simultaneously needs ~15 Mbps upload headroom
Frequently Asked Questions
Should an ADU have separate internet service?
For a rental ADU with a tenant, separate service is strongly recommended. It keeps billing clear, gives the tenant privacy and autonomy, and eliminates support conflicts (whose router needs restarting?). Check whether the ISP will provision a separate service at the ADU address — some ISPs serve secondary structures as a separate address on the same property. If separate service is unavailable or too expensive, use fiber cable to extend the connection with full network isolation via VLAN.
Can I just share Wi-Fi with the ADU?
Rarely successfully for long-term use. Plain Wi-Fi through exterior walls — especially stucco, concrete, or wood siding — is unreliable and private. If the ADU is within 5–10 meters with clear walls, a mesh node can work. For anything farther, use fiber, MoCA over existing coax, or a point-to-point wireless bridge for dependable throughput and proper network isolation.
How much internet speed does an ADU need?
One or two residents are comfortable at 100–300 Mbps for streaming, calls, and general use. The more important number is upload: if both the main house and ADU are simultaneously doing video calls, make sure the shared upload capacity (typically 10–50 Mbps on cable) can handle both without one saturating the other.
Why can't I just run regular Ethernet between buildings?
Copper Ethernet between separate buildings carries electrical ground potential between them. A lightning strike on either structure, or a power fault, can travel through the cable and damage equipment at both ends — or create a shock hazard. Fiber optic cable has no electrical conductors, so it is safe for cross-building runs. Always use fiber (with media converters) for any cable run that goes outside between two separately grounded structures.