So, you’re joining the small living movement. Whether it’s a sleek tiny house on wheels or an Accessory Dwelling Unit (ADU) in the backyard, you’re trading square footage for freedom and efficiency. It’s an exciting prospect. But let’s be honest—the plumbing? That’s where many DIY dreams can, well, go down the drain if you’re not careful.
Plumbing a small space isn’t just about shrinking a standard house’s system. It’s a different beast altogether. You’re working with limited space, unique water and waste disposal needs, and often, a completely different set of codes. But don’t let that scare you. With the right planning, you can create a system that’s not just functional, but brilliantly efficient.
First Things First: The Big Three Questions
Before you buy a single pipe, you need to answer three fundamental questions. Your entire plumbing strategy hinges on this.
1. Will You Be On-Grid, Off-Grid, or Somewhere in Between?
This is your starting point. An ADU is almost always connected to the main house’s utilities—on-grid plumbing. A tiny home on a foundation can be, too. But a Tiny House on Wheels (THOW)? That’s a whole other story. You’re looking at a self-contained system.
2. How Will You Source Your Water?
Your options here define your setup:
- City/Main House Connection: The simplest if you have access. You’ll need a standard pressure regulator and hose bib connection.
- Freshwater Tank: Common for mobile tiny homes. You’ll need a 12v or 110v water pump to create pressure. Think of it like a more sophisticated version of an RV system.
- Well Water: Possible for stationary ADUs and tiny homes, but requires a pump and pressure tank—which eats up space.
3. Where Will Your Wastewater Go?
This is arguably the most critical consideration. You can’t just let it… disappear.
- Septic or City Sewer Tie-In: The gold standard for ADUs and permanent tiny homes. It’s a permanent, hands-off solution.
- RV-Style Hookups: For THOWs parked in locations with facilities, you can use a standard 3-inch sewer hose to connect to an RV dump station.
- Greywater Recycling System: A fantastic eco-option. This system filters water from sinks and showers for reuse in toilet flushing or irrigation. It complicates the plumbing but seriously reduces your water footprint.
- Composting Toilets: A game-changer for off-grid living. They eliminate blackwater (sewage) entirely, meaning you only have to deal with greywater from sinks and showers, which is much easier to handle or dispose of.
Choosing Your Plumbing Materials: It’s Not Just About Price
In a standard home, you might not think twice. But in a tiny home, every pound and every inch counts, especially if it’s on wheels. The weight of your water system is a major factor for THOWs.
| Material | Pros | Cons | Best For… |
| PEX (Cross-linked Polyethylene) | Flexible, easy to install, freeze-resistant, lightweight. | Can be damaged by UV light, requires special crimp tools. | Almost all tiny homes and ADUs. The modern go-to. |
| CPVC (Chlorinated Polyvinyl Chloride) | Rigid, inexpensive, easy to cut and glue. | Can become brittle over time, less flexible for tight spaces. | Budget-conscious, stationary builds (ADUs). |
| Copper | Durable, long-lasting, professional look. | Expensive, heavy, requires soldering skills, can freeze and burst. | Permanent ADUs where budget isn’t a primary constraint. |
Honestly, for most tiny home projects, PEX is the winner. Its flexibility is a lifesaver when you’re snaking lines through tight, irregularly shaped walls. And that freeze-resistance? A nice peace-of-mind bonus if you ever lose heat in winter.
Space-Saving Fixtures: The Fun Part
This is where you get to be clever. Standard fixtures are space-hogs. Here’s how to beat the system:
- Tankless Water Heaters: Absolutely essential. They hang on a wall and provide endless hot water on demand, using less energy than a traditional tank. No more waiting for a 40-gallon tank to heat up. For electric models, just be sure your electrical system can handle the load.
- Corner Sinks & Slim-Profile Tubs: Utilize every nook. A small, deep corner sink can be more useful than a wide, shallow one. And if you crave a tub, slim Japanese-style soaking tubs are a brilliant compromise.
- Wall-Mounted Toilets & Vanities: By mounting these off the floor, you create a visual sense of space and make cleaning a breeze. It’s a small touch with a big impact.
- Venting and Drainage Tricks: In a tiny home, you can’t always follow the traditional plumbing venting rules. That’s where Air Admittance Valves (AAVs) come in. These one-way valves allow air in to prevent siphonage in drains but don’t let sewer gas out. They can save you from running a vent pipe through your roof, simplifying the build immensely. Check your local codes, though—some areas are picky about them.
Winterization and Insulation: Don’t Get Frozen Out
If your tiny home or ADU will ever experience freezing temperatures, this isn’t optional. It’s mandatory. A single burst pipe can be a catastrophic disaster in a small space.
For stationary units, insulate all pipes, especially those in exterior walls. For THOWs, you need a multi-layered defense:
- Skirt the Base: Installing a skirting around your trailer blocks wind from sucking the heat out from under your home.
- Heat Tape: Wrap vulnerable pipes with thermostatically-controlled heat tape.
- Drain-Down Systems: The ultimate protection for a vacant THOW. With a series of strategic valves, you can drain every single drop of water from your entire plumbing system in minutes. It’s the equivalent of putting your plumbing into hibernation.
A Final Thought: Simplicity is Sophistication
When you’re laying out your plumbing for a tiny home or ADU, remember that complexity is the enemy of reliability. Every extra fitting, every complicated loop, is another potential failure point. Aim for the simplest, most direct routes possible.
The goal here isn’t to replicate a mansion’s plumbing in miniature. It’s to design a smart, resilient system that supports a life lived large, no matter the square footage. Plan meticulously, choose your components wisely, and you’ll build a foundation for your small home that works as beautifully as it lives.
