Build Yourself an Indoor Outhouse

The author's indoor outhouse design allows for the most convenient siting of your commode while enabling relatively convenient waste management.


| March/April 1983



indoor outhouse diagram

Zandy Clark's indoor outhouse design.


Illustration by MOTHER EARTH NEWS Staff

You can chase the winter outhouse blues away, just as I've done, with a composting toilet. You'll have to invest only about $150 and a few days' effort to come up with a unit that rivals the best of the Swedish designs, and yours will be customized to fit that inevitable tight spot in your home. My own waterless throne is stuck in a cold crawl space where no regular composter would even fit — let alone work properly, since the location is far from my home's sources of heat. Yet my "indoor outhouse" functions so well that I've been asked to build 15 others, and have easily gotten a patent on the design.

There are three basic tricks to my design, and they can be applied in any situation. First, don't bother building a complicated trapezoid-shaped holding tank such as you might find in a commercial composter. Instead, just make a simple rectangular box. Next, suspend the compost bed on a sloping grid, so air can reach the pile from below. (Forget the idea of channels or louvers to get air inside the pile. They'll clog up before long.) And third, include a drain or bypass for excess liquid. (Even the warmest composting toilets equipped with a forced draft will have to be bailed out if too many people use them too often.)

Here’s how these tricks are applied. The bed of compost is suspended on a grid made from old 3/4" galvanized water pipe (rebar would do just as well). I don't think the slope is crucial, but 45° seems to work fine. To get things started, you'll need to spread hay or grass clippings over the grid to form a bed. Then add peat moss, leaf mold, topsoil, or compost to introduce the soil organisms that'll do the decomposition work. (Contrary to popular belief, no special proportions of these are necessary.) Once the compost bed is established the hay will break down, but the knitting action of the continuing biological process will keep the bed suspended. That way, air can pass up through all the compost, facilitating the aerobic reaction and helping to evaporate moisture.

The rectangular box can be built from fiberglass-covered plywood or with dry-stacked concrete blocks covered with surface-bonding cement. My design is for a block-walled unit 4 feet square and 3 feet high, but the size can be varied.

Most surface-bonding cements (I prefer Surewall by Bonsal Corporation) are waterproof, a quality that eliminates the need for any later sealing work. Consequently, the whole job can be done in one quick operation (it takes two people about four hours to lay, shim, and stucco a block box). Of course, if you get real fussy about shimming and setting the blocks to plumb, it could take longer; just remember, you're building a toilet, not a cathedral.

A plywood version has proved appropriate for a composting toilet I designed for a boat shop on a wharf, since the 4' x 8' assembly is hung from the floor joists of a drying shed. When the pilings shift with ice and tides, the box moves with them and isn't harmed. The boatbuilders traded a cozier indoor incinerating toilet for my chilly outdoor model, because the propane- fired device cost a lot to run, threatened to burn down the shop, and produced poisonous hydrogen sulfide gas.

nbarbour
5/28/2012 1:27:52 AM

Based on your picture I don't see how the liquid bypass captures the liquid. Is it the equivalent of a urinal? If so how does that work for women?


dave chambers
10/22/2008 5:05:50 PM

Can the pit and drain work on a relatively flat location? As in a camp with no foundation.






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