How to Build a Composting Toilet From Scratch

How to Build a Composting Toilet From Scratch

Composting toilets provide an eco-friendly and sustainable alternative to traditional flush toilets. They don’t require any water or sewer connections, and instead use natural processes to break down human waste into usable compost. Building your own composting toilet from scratch can be a fun and rewarding DIY project. Here is a step-by-step guide on how I built my own composting toilet from start to finish.

Choosing a Design

The first step is deciding on a design for your composting toilet. There are two main types to choose from:

Self Contained Toilets

These have a single tank or chamber where waste is deposited and composted. Self contained toilets are compact and all-in-one, but require frequent emptying. Popular prefabricated models include Nature’s Head and Airhead.

Continuous Composting Toilets

Continuous composting toilets have separate chambers – one for active composting and one for finished compost storage. Waste gets transferred from the active chamber to the storage chamber after the composting process finishes. This allows for less frequent maintenance. The Phoenix Composting Toilet is a great example of a continuous design.

I opted to build a continuous composting toilet as I wanted something low maintenance that could handle full-time use. The separate chambers make it easy to get at finished compost without disturbing the active composting chamber.

Planning the Design and Layout

Once I had decided on a continuous composting toilet, I mapped out the major components I would need:

  • Active composting chamber
  • Storage/drying chamber
  • Chute/passage between chambers
  • Vent pipe system
  • Toilet seat/housing unit

I sketched up some simple plans to visualize the layout and made a list of the building materials I would need. Planning it out ahead of time ensured I had all the right parts ready before starting.

Acquiring Materials

Building a composting toilet requires the following materials:

  • Two plastic storage bins – I used a 56 gallon bin for the active chamber and 20 gallon bin for the storage chamber.
  • 4″ PVC pipe – used to construct the main vent stack.
  • 1.5″ PVC pipe – for the urine diverter.
  • 5″ computer fan – provides ventilation.
  • Plywood – for constructing the frame and toilet housing.
  • Toilet seat – make sure to get one sized for your toilet housing.
  • Wood shims – for sealing and joining bins.
  • PVC cement and primer – for gluing pipes.
  • Screws and bolts – for securing parts.
  • Insulation – helps moderate internal temperatures.
  • Carbon additive – for compost balancing.

I was able to source most of these materials from my local hardware store. The total cost was around $250. Shop around to find the best deals on bulk pricing.

Constructing the Composting Chambers

With my materials gathered, it was time to start construction. I began by using plywood to build a secure frame for mounting the two plastic bins.

Active Composting Chamber

For the active chamber, I cut a 10″ x 10″ square opening in the plastic bin about 8 inches up from the bottom. This opening allows waste to transfer into the storage chamber below once composting is finished.

I used PVC cement to mount a 4″ diameter ventilation pipe to the underside of the bin lid. This pipe needs to stretch from the active bin all the way up and out of the bathroom ceiling. Proper ventilation prevents odors and helps evaporate excess moisture.

Storage Chamber

The storage chamber acts as the leachate collection area. I drilled a 2″ drainage hole about 3″ up from the bottom of this bin. I attached a flexible hose here to allow easy draining.

I used wood shims around the top opening to create an airtight seal between the two chambers. I also cut access doors in the side of the bin for easy compost removal.

Installing the Urine Diversion System

In a composting toilet, separating the urine from the solid waste helps control excess moisture and prevent odors. This is accomplished through a urine diverter.

I constructed a simple urine diverter using a 1.5″ PVC pipe fitted into the toilet housing. This angled pipe directs urine into a small collection tank separate from the composting chamber.

Making sure the urine diverter achieves a good seal against the toilet housing is crucial for proper diversion. I used silicone caulk around the edges to prevent leaks.

Building the Toilet Housing Unit

With the composting chambers complete, I now needed to construct the toilet housing that would sit on top. This houses the toilet seat and interfaces with the user.

I built a simple toilet housing out of plywood and 2x4s. I made sure to size it to fit my toilet seat and allow comfortable leg room. The housing has a removable back panel to allow easy access into the composting chamber below.

I cut a 8″ x 8″ hole centred over the active chamber opening. I mounted the urine diverter pipe along the front of the housing. After securing the toilet seat in place, my composting toilet housing was ready for installation!

Installing Ventilation

Proper ventilation is vital for evaporating excess moisture and preventing unpleasant odors. Passive ventilation relies solely on air rising up and out of the vent stack.

For improved airflow, I installed a 5″ 12V computer fan near the top of my vent stack controlled by a simple toggle switch. This provides active exhaust when needed.

I mounted the vent stack vertically in a corner of the bathroom and ran it up through the ceiling and roof. Having over 15 feet of vertical rise creates necessary draught.

Final Installation and Operation

With all the main components assembled, I secured the chamber frame into a corner of my bathroom. After connecting the vent stack and routing the urine diverter, the composting toilet was ready for use!

To operate, I simply add a few scoops of wood shavings after each use to balance out the nitrogen. About once a year I’ll transfer finished compost from the active chamber into the storage chamber. And when the storage chamber fills up, the compost gets emptied out for use in non-edible gardens.

While involved, building my own composting toilet was very rewarding. I now have an sustainable, eco-friendly bathroom fixture that earns its keep by producing useful compost. Let me know if you have any other questions about DIY composting toilets!