How to Build a DIY Composting Toilet

outhouse in desert under grey sky - how to build a diy composting toilet

Everyone, it’s about to get a little blue. A DIY composting toilet might not top the list of upgrades the average homeowner plans on tackling this year, but there are some excellent reasons to consider it.

When people think about a composting toilet, they often think of an outhouse, which is not the same thing. In an outhouse, human waste just sits. It’s why they smell so bad.

Composting toilets, on the other hand, are indoor dry toilets that are specifically designed to turn human waste into, as the name suggests, compost. Like any composting process, they use carbon- and nitrogen-rich organic matter, moisture, heat and oxygen to create the right conditions for aerobic bacteria to break down the waste into usable fertilizer.

Before we get too far, though, we should get two big questions out of the way. Question #1—do they smell? By all accounts, no. If you take care of them properly. Question #2. Is this even legal to have in your home? By all accounts, yes, although checking with local regulators about building code compliance should always be the first step of any renovation project.

Ame Vanorio of the Fox Run Environmental Education Center explains that some jurisdictions actually encourage composting toilets as a way to reduce stress on water and sewage infrastructure. She cites such respectable locations as the Bronx Zoo and the University of Vermont as examples of organizations that have begun to use composting toilets in their own facilities.

Who Would Do This and Why?

Unless you feel very strongly about minimizing water use at home, composting your own waste is likely going to be most attractive to people living off-grid, whether that’s in a tiny home, a cottage or cabin or an RV. People who want to limit their reliance on a septic system, or avoid having to install a septic system altogether, might also be especially interested in a composting toilet.

For people living off-grid, a composting toilet can be an important part of a water and energy management system. Properly maintained, the compost from the toilet also provides a natural fertilizer for gardens and, some people argue, for crops.

Types of Composting Toilets You Can DIY

The Bucket System

The very simplest systems consist of a bucket with a nearby store of sawdust or other fine, organic matter to cover waste and soak up excess moisture. Most folks simply do not wish to live their lives this way, so they add a plywood box and a toilet seat.

When the bucket is filled, the contents are dumped in an outdoor compost heap (which we’ll discuss below). The bucket is then cleaned, disinfected and returned to the bathroom. A few scoops of sawdust at the bottom of the bucket and it’s ready to go again.

Self-Contained Toilets

Self-contained toilets include a composting chamber right underneath the toilet bowl. The urine drains away into a separate chamber. That chamber might need to be emptied regularly. It might also be directed down a drain or evaporated, depending on the style of toilet.

Aerobic bacteria break down a mix of solid waste and bulking material like peat moss in the composting chamber itself. The solid waste inside needs be turned over and oxygenated by rotating the container via a crank or handle.

A finishing drawer collects the compost after it’s been processed. When you empty the drawer, it will ideally be ready to use on the garden.

Electric versions of this type of composting toilet might incorporate a heating element to help evaporate liquid waste and a powered venting system. Non-electric versions, of course, will be simpler to build yourself.

Central Systems

A more involved building project involves a container collection system where the toilet is hooked up to pipes that direct waste to a larger tank. This tank can be outside or indoors, somewhere below the toilet. The system can be waterless or micro-flush. They typically incorporate some kind of vacuum or venting system to keep odours away.

The composting chamber operates in a similar fashion to self-contained units. These systems separate urine from solid waste, either by diversion or drainage, directing it either to a holding tank that will need emptying, to a drain pit or to a septic or sewer.

These central systems are an ambitious DIY project. They’re also more convenient for larger households, however, because they have a greater storage capacity and because multiple toilets can be hooked up to the same system.

Building the DIY Composting Toilet

wooden outhouse by cedar trees - how to build a diy composting toilet

There are a lot of free plans online to give you specific guidance on the actual build. The majority of plans you’ll find online are for bucket-type systems. Here are some of our picks.

Farming My Backyard offers a step by step tutorial on making a very basic composting toilet with a bucket and a frame made of plywood and 2 x 4s.

These plans from Green Citizen include a urine diverter. There’s a more involved bucket to barrel composting system from David Omick here. He has a video tutorial for a 55-gallon barrel system here.

Driving Home offers video instructions for this DIY version of a self-contained toilet.

Composting the Waste

If you DIY a composting toilet, you’ll also need a well-functioning compost pile. Most sources recommend a three bin composting system. With three bins, you’ll have one compost pile that you’ll be actively filling, one pile that’s curing and one usable pile. Each compost pile should cure for a year so it can decompose absolutely and completely.

The goal is to create a thermophilic compost system that will reach temperatures of at least 131F. At that temperature, pathogens will be killed off and thermophilic bacteria will break down waste.

Contrary to what you might think, toilet paper is essential in this process. Urine contains high amounts of nitrogen, which makes it a “green” material. That needs to be balanced with carbon-rich (“brown”) materials. Toilet paper, as well as bulking materials like sawdust, peat moss, dried leaves or chopped straw are all carbon-rich and they’re necessary for your waste to decompose properly and to create quality compost.

Human waste composting pioneer Joseph Jenkins advises that you start your compost pile with a generous layer of brown materials. Whenever you add your bucket contents, cover with another generous layer of carbon-rich material.

When the pile is large enough, he advises, shovel out a well in the centre and dump the bucket contents in the middle to help them break down more quickly. Don’t turn the compost—making holes for new green materials is enough to aerate the pile. After a year, start a new pile and let the old one sit.

Final Thoughts

There’s a lot of debate about whether the composted waste from a toilet is safe to use on food crops. This article is not going to step onto that minefield, but you should be aware of those debates and do your research to determine your best and healthiest options.

For further reading, The Humanure Handbook by Joseph Jenkins and the B.C. Ministry of Health’s Manual of Composting Toilet and Greywater Practice are excellent resources.

Feature image: Grant Durr; Image 1: Jennifer Lim-Tamkican

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