Internet to an ADU, a Converted Garage or a Backyard Office: Do It in This Order

A new ADU going up in the backyard. A garage becoming a studio. A shed at the end of the lot that is now somebody's office three days a week. The building work gets planned to the inch — foundation, panel, water, sewer, setbacks, permits — and then somewhere near the end of it somebody says "what about wi-fi out there?", and the answer is a thirty-dollar extender plugged into a window facing the yard.

It disappoints almost every time, and not because the extender is bad. It is because the question was asked in the wrong order. Getting a connection to a detached building is five decisions, and only the last one is about hardware. Four of them are free to make and expensive to change afterwards, and one of them — the cheapest, best answer in the whole article — has a deadline measured in days.

This is the order we would work through it, on a job we were doing ourselves.

First decision: one internet service, or two

Everything downstream depends on this, so settle it before anyone prices a cable. Either the detached building gets its connection from the house — one account, one modem, one router, extended outward — or it gets its own service, its own bill and its own equipment, and the two buildings never touch electrically or on the network.

For an owner using the space themselves — office, gym, guest room, workshop — extending the house line is nearly always right. You already pay for it, the speed is already there, and one network is simpler to live with.

For a long-term tenant, a second account is usually the cleaner answer even though it costs more, and the reasons are not technical. You never become somebody's internet provider. Their outage is not your phone call at eleven on a Sunday night. Their traffic does not come from your address. And nothing they do — a torrent client, a security camera uploading all day, a device that gets compromised — lands on the connection your work depends on.

The operative fact for the provider is the address. An internet company's serviceability system is an address database: it will happily sell a second line to "1234 Elm St, Unit B" and be unable to find "the back house at 1234 Elm St" at all. So the practical test is to put the ADU's assigned address into the provider's own availability checker once the address exists, and to ask directly whether they will open a second account at that unit designation. Policies differ between companies and change, which is exactly why it is a question to ask rather than an assumption to make.

What state ADU law says about "a separate connection" — and why the internet is not in that sentence

This trips people up, because "you cannot be made to install a separate utility connection" gets repeated on ADU forums as though it settles the internet question. It does not, and it is worth reading what it actually says.

California's Department of Housing and Community Development publishes an ADU Handbook — the January 2025 edition is the current one — and its Utilities section answers the question head on. ADUs and junior ADUs created from the existing space of a primary dwelling or accessory structure under Government Code section 66323(a)(1) "cannot be required to install a new or separate connection unless the ADU is constructed concurrently with a new single-family dwelling." For all other ADUs, "a new or separate connection directly from the utility to the ADU may be required" (Gov. Code, § 66324, subds. (d), (e)).

Read who that binds. It is about local agencies, special districts and water corporations — water and sewer, connection fees and capacity charges. The handbook is explicit that HCD has no authority over the gas and electric side either, and points people to the CPUC or their municipal utility for those.

Broadband is not in that conversation at all. No rule requires you to take a second internet line for an ADU, and no rule entitles you to one — the internet company decides by address and by what is physically in the ground on your street. The useful takeaway is a defensive one: when a contractor says "utilities are handled," that sentence does not include the internet. Nobody's trade owns it, which is precisely why it ends up being solved with an extender in a window in the last week of the job.

If the unit could ever be sold separately, wire it as a building and not as a branch

A change most homeowners have not heard about: AB 976 and AB 1033 (both 2023, in effect since 1 January 2024) authorised a local agency to adopt an ordinance allowing the primary dwelling and the ADU to be conveyed separately as condominiums, under Government Code sections 66340 to 66342. The HCD handbook lists the conditions — the condominiums are created under the Davis-Stirling Common Interest Development Act and in conformance with the Subdivision Map Act, a safety inspection is required before the condominium plan is recorded, lienholders have to consent, and the homeowner has to notify the utilities.

This is permissive, not statewide: it only exists where your city has actually adopted such an ordinance, so check with your own planning department rather than assuming. But if there is any chance the unit is sold one day, it changes what you should build now. A separately owned unit cannot sensibly hang off the seller's router. Give it its own conduit path back toward the street side of the property, its own equipment wall with power and a little ventilation, and its own router — so that "separate the internet" is a phone call later rather than a trench.

Note the second-order effect too. A Davis-Stirling condominium means an association, and an association means association rules — which is a world with its own protections and its own limits, particularly around dishes and outdoor antennas.

The garage case is a relocation job before it is a coverage job

If the detached building is a garage being converted, there is a step that comes before any of the coverage questions, and it is the one people discover after the drywall is up.

The garage is usually where the network already lives. It is where the phone or cable line entered the building, where the fibre terminal was mounted, where the modem and often the router sit on a shelf beside the panel, and where the coax splitter is. Converting that garage does not just create a room that needs wi-fi — it puts your entire home network inside somebody's bedroom wall, or on the far side of a newly insulated stud wall, or behind a wardrobe.

So the sequence is: move the network into the house first, then solve coverage. The provider's equipment is the part you do not move yourself — the terminal on a fibre service belongs to them and they will relocate it, usually as a scheduled appointment. Everything downstream of it is yours to move. The whole exercise is cheap while the walls are open and the electrician is on site, and genuinely expensive four weeks later.

While you are at it, and for the same labour: pull two or three Cat6 runs from wherever the equipment is going to live — to the far corner of the house, to the TV wall, and out toward the detached building. The cable costs very little. The access to the cavity is the expensive part, and it is open exactly once.

The one week the wire is cheap is the week the trench is open

If the ADU is new construction, there is a trench for the electrical feed and usually for water. That week is the cheapest a buried data cable will ever be, by a wide margin, and it closes without warning.

What to put in it: conduit, not bare cable. Even if you use direct-burial-rated cable — and you should — pulling it inside a conduit with a spare pull string means the cable you install today is not the cable you are stuck with in twelve years. Fibre gets cheaper, standards move, rodents happen. Conduit turns a future upgrade into an afternoon.

What kind of cable: an outdoor-rated one. Cable makers are clear that outdoor jackets need to be UV-resistant polyethylene rather than the ordinary indoor jacket, and that direct-burial-rated cable adds water-blocking — gel filling or water-blocking tape — so that moisture cannot wick down the inside of the cable. Indoor cable in a wet conduit fails slowly and confusingly, months later, as a "the internet is weird in the ADU" problem.

What not to do: never put the data cable inside the same conduit as the power conductors. Installers keep meaningful separation between the two — a foot is the common rule of thumb — and where they share a trench, that separation and the burial depth are things your electrician and your inspector decide, not a forum. Typical guidance for depth is on the order of twelve to eighteen inches, but the trench you are sharing has its own rules and they win.

Two more things that cost nothing at trench time and are impossible later: pull more than one cable — two Cat6, or better, one Cat6 and one fibre, for the reason in the next section but one — and leave a generous slack loop coiled at both ends. Then photograph the open trench with a tape measure in frame before it is backfilled. In five years, when somebody wants to plant a tree or add a patio, that photo is the only record of where the line runs.

The distance limit is not 328 feet once you go outdoors

The number everyone quotes for Ethernet is 100 metres — about 328 feet. That comes from the structured-cabling standard, and it is a channel budget rather than a single cable: 90 metres of fixed horizontal cable plus about 10 metres of patch leads at the two ends.

Outdoors, cable manufacturers derate it, and the reason is physics rather than caution. Copper's resistance rises with temperature, and a cable in a sunny conduit or a hot attic run is nowhere near the lab conditions the standard assumes. trueCABLE, for instance, tells installers to restrict outdoor runs to 250 feet for unshielded and 275 feet for shielded cable. Treat something in that range as your working ceiling.

The trap is that people measure the wrong distance. A building that is 150 feet away as the crow flies is rarely a 150-foot cable: the real route goes up an interior wall, along the joists, out at the eave, down to the trench, along the trench dodging the water line, up into the ADU, along its ceiling and down to where the equipment actually goes. Two hundred and forty feet is a normal answer for a 150-foot yard. Measure the route with a string, then add twenty per cent.

If you are over the limit, the answer is not a longer cable. It is fibre, which does not care about the distance at any length a residential lot can produce; or a powered switch at a midpoint, which means finding it power and weatherproofing it; or going wireless. Fibre, at these distances, is genuinely the least fuss.

The part nobody tells homeowners: copper between two buildings ties their grounds together

This is the reason a trade installer reaches for fibre between buildings and a weekend how-to article does not, and it is worth understanding even if somebody else does the work.

Two structures have two electrical ground references. They are supposed to be bonded to the same grounding electrode system, and where the work has been done properly they are — but a shielded Ethernet cable, or the ground path through the equipment at each end, physically ties the electronics in one building to the electronics in the other. The trade press describes the consequence plainly: "If the ground potentials of Building A and Building B are different, a ground current flows in the data line," and there are documented cases where "the potential difference has burned open data cables."

The dramatic version is lightning, and the arithmetic is sobering: a 10,000-amp lightning current flowing through a building's ground impedance of a tenth of an ohm produces a thousand-volt transient rise on that building's ground — while the other building sits somewhere else entirely. Everything bridging the two takes the difference. Southern California is not a lightning belt, which takes the worst case off the table for most of our customers, but the everyday version does not need a storm: a new sub-panel at the ADU, a pool pump, a well, an EV charger, a solar inverter, or simply a marginal bonding job will produce a difference all on its own.

The fixes, in the order we would choose them. Fibre between the buildings is the clean one — glass carries no current, so the two structures stay electrically separate while the data crosses; you either use small media converters at each end or a switch with an optical port. A wireless bridge has exactly the same virtue and nobody ever mentions it: there is nothing conductive between the buildings at all. And if it must be copper, then it is shielded cable properly bonded with shielded hardware, with surge protection at both ends, bonded to the grounding electrode system rather than to some rod driven in on its own.

That last sentence is where we stop and a licensed electrician starts. Bonding and grounding between structures is their trade, it is inspected, and adding an unbonded ground rod at the ADU because a video suggested it makes the situation worse rather than better. The honest summary for a homeowner is short: if there is a trench, put fibre in it and the entire problem disappears.

If the trench is already filled: the honest ranking

Most people find this article after the concrete has cured, so here is what actually works, best first.

One — coax that already goes out there. Older detached garages very often have a TV drop, and that cable can carry a fast, stable wired link using MoCA adapters. If the coax exists and is continuous, this beats every wireless option and costs less than most of them. We have written up the mechanics separately.

Two — a point-to-point wireless bridge. A pair of small radios, one mounted at each building, aimed at each other with clear line of sight. This is not an extender: it is a dedicated link between two antennas that are pointed at each other, which is why it performs like a wire and an extender does not. Requirements are honest and non-negotiable — a clear path (a wall, a tree in leaf or a van parked in the driveway all matter), a mount at each end that will not drift, and power, which is usually delivered up the same cable.

Three — an outdoor access point on the ADU, fed by the best link you have. If you got a wire or a bridge out there, this is simply what you put at the far end.

Four — a mesh node with a wireless backhaul. It can work at short range with a clear window-to-window path. Through two exterior walls and forty feet of yard it usually disappoints, because the node is spending half its airtime talking back to the house.

Five — powerline adapters. On a detached building this is where powerline is at its weakest: the ADU is frequently on its own sub-panel or a long feeder, and the signal has to travel the whole path. It is cheap enough to try and returnable if it fails, but do not plan around it.

And a legitimate sixth that is not a compromise: give the ADU its own service by 5G home internet or satellite. If there is no path, or if the unit is a rental and you want the networks genuinely separate, that is a good answer rather than a fallback.

Whose network is it? The question that decides the far-end hardware

If the detached building is on your internet line, the devices in it are on your network by default — and that means anyone in that building can see the shared folders on your PC, your network drive, your printer, your cameras and anything else that trusts the local network. It also means you can see theirs. With a family member using it as an office, fine. With a tenant, both directions are a problem, and the one that gets people into trouble is the second one.

Three ways to separate them, in increasing order of properness. A guest network with client isolation turned on: available on nearly every router sold in the last decade, takes two minutes, and keeps the ADU's devices from reaching anything of yours. A separate network name mapped to its own VLAN: the correct answer, needs a router and access points that support it. Or a second router of their own hanging off one of your LAN ports, which gives them a completely separate network for about eighty dollars — the side effect is a double layer of network address translation, which is invisible for browsing and streaming and occasionally irritating for game consoles, some VPNs and remote camera access.

Then there is the part that is not about hardware at all. If the ADU depends on your router, your outage is their outage, your reboot is their dropout, and your password change strands their television. You are, functionally, their internet provider — at whatever hour it breaks. If it is a tenancy, write down what is included and what happens when it goes down, before it goes down.

Cameras, microphones and somebody else's home

A camera covering your driveway and your own front door is ordinary. A camera covering the ADU's door, its window or its parking space is a different thing once somebody lives there, and it is worth being deliberate rather than accidental about it.

The audio is the part that catches people out. California requires the consent of all parties to record a confidential communication — Penal Code section 632 — and most doorbells and outdoor cameras record sound by default, over a range that easily covers a conversation on a step. The microphone can be switched off in the app on essentially every current camera, and on any camera pointed anywhere near a private area, switching it off is the simple move.

Our practical rule: aim cameras at the approaches to your property rather than into somebody's home, tell people what exists rather than letting them discover it, and turn the audio off where it overlaps a private space. Where it becomes a tenancy question, that is one for a lawyer rather than for us.

Where the far-end equipment lives, and what keeps it alive

The gear at the detached end usually gets put wherever there is a spare outlet, which in a garage or a shed means the floor, the back wall, or a shelf next to the water heater. Heat, dust and damp are all worse out there than in the house, and network equipment fails quietly under all three. Mount it on a wall, off the floor, out of the sun and away from anything that can leak.

The other thing worth knowing: if the ADU is fed from the house, the whole link runs through the house's equipment. A small battery backup on the house router and the fibre terminal keeps both buildings online through a brief cut, which matters more than it sounds when somebody out there is on a video call for a living.

And label both ends of every cable you run. It takes a minute and saves an hour, and the person it saves it for is probably you, four years from now, standing in the garage holding two identical white cables.

The order, on one page

One: decide whether the detached building is on your internet service or its own, and if there is any chance it will be sold separately, treat it as its own building from the start.

Two: if it is a garage conversion, move the network equipment into the house before the walls close.

Three: if there is a trench, put conduit with a pull string in it, and put both a Cat6 and a fibre inside — this is the whole ballgame and it lasts about a week.

Four: measure the real cable route, not the straight line, and keep it inside roughly 250 feet of copper or use fibre.

Five: never share a conduit with the power conductors, and let the electrician own the bonding between the two structures.

Six: if the trench is gone, use existing coax with MoCA first, a point-to-point bridge second, and an extender never.

Seven: decide whose network it is before you plug anything in — guest network with isolation at the very least, a separate router if a tenant is involved.

Eight: mount the far-end equipment high, dry and labelled, and put the house router on a battery.

How we can help

This is a job we do regularly across Southern California, and the most valuable phone call is the early one — before the trench is filled, not after. We will walk the route with you, tell you honestly whether it is a wire, a fibre or a bridge, specify what to put in the trench so your electrician or general contractor can drop it in while they are already digging, and come back to terminate and configure once the building is closed in.

On the network side we do the whole thing: the run itself where it is ours to do, the access point at the far end, the separation between your network and a tenant's, and getting the printer, the cameras and the smart-home gear to behave once there are two buildings instead of one.

What we do not do is pull the permits, dig the trench or touch the bonding between the structures — that is your contractor and your electrician, and we will tell you plainly when a question belongs to them. The coordination is usually the part that saves the money, because the cheap version of this job and the expensive version differ by about one week of timing.