The Owner Built Home and Homestead: Human Composting Privy

Ken Kern shares information and plans to build a human composting privy using aerobic composting methods for the homestead.


The "healthful" aspects must be considered. It can be factually stated that the conventional water toilet is not healthful. The high sitting position is artificial and unhygienic.


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Ken Kern, author of The Owner-Built Home and The Owner-Built Homestead, is an amazing fellow and everyone interested in decentralist, back-to-the-land, rational living should know of his work. Back in 1948 he began collecting information on low-cost, simple and natural construction materials and techniques. He combed the world for ideas, tried them and started writing about his experiments. Eventually, Mildred Loomis started publishing Kern's articles in The Interpreter, Way Out and Green Revolution. Ken has also issued a three year series of pieces (called Technic) on his own and a greenhouse-sun pit design of his has been featured in Organic Gardening. 

This installment of Ken's work is taken from The Owner-Built Home. I'll be featuring never before published material from The Owner-Built Homestead in my No. 7 issue. Again, I have to apologize for jumping back and forth as I reprint Ken's excellent material, but that's the way I have to do it and Ken's writing makes it all worthwhile. 


The Homestead Building Site: Human Composting Privy

"Modern architecture is a revolt against styles and is based on the intimate awareness of functional requirements in the broadest sense of the word "function". Unfortunately, the revolt preceded the research needed to start establishing these functions."  

Architects Journal, 1965  

In this multi-volumed and progressively-written book I have attempted to present the results of my research precisely along the lines of the functional revolt—as applied to the low-cost or owner-built home. In the course of my thinking and writing, I have been guided somewhat by readers' comments and questions on previous chapters. These have constituted a kind of feed-back on my researches. What were the readers' particular problem areas? Such considerations should assist in the formation of new chapters or supplements—even new volumes or books.

The present chapter is a definite response to readers' comments. More readers picked up an offhand mention of the squat-toilet (p. 38) than any other item in Volume III. So the squat-toilet idea will be discussed here. And it will be discussed in its proper context as a feature of the large problem of bathroom waste disposal. A proper toilet suggests a proper disposal system and this further suggests a proper structure to accommodate the necessary facilities.

And by "proper" I refer, as usual, to Ralph Borsodi's criteria: Is it healthful? Is it economical? Is it pleasing to behold? One need not be reminded that modern bathroom systems are ugly, expensive and unhealthful. If you wish to know how much your conventional bathroom plumbing and drainage system costs, count the number of fixtures in the house, including lavatories, water closets, bathtub, water heater. This total multiplied by $400 gives a close estimate of plumbing costs. Add to this the room area multiplied by $10 and you have a surprising total of about $2500 for an average-size bathroom and drainage facility.

Finally, the "healthful" aspects must be considered. It can be factually stated that the conventional water toilet is not healthful. The high sitting position is artificial and unhygienic. Nor is it healthful to pollute bodies of water with water-borne sewage. Each year 4.5 million tons of sewage sludge is dumped into the oceans from North America. This represents 4.5 million tons of nitrite contaminant and it also represents 4.5 million tons of potentially valuable fertilizer not returned to the land. The experts are in unanimous agreement on the subject of toilet height (as quoted from Kira's book):

The ideal posture for defecation is the squatting position, with the thighs flexed upon the abdomen. In this way the capacity of the abdominal cavity is greatly diminished and intra-abdominal pressure increased, thus encouraging the expulsion of the fecal mass. The modern toilet seat in many instances is too high even for some adults. The practice of having young children use adult toilet seats is to be deplored. Beckus, Gastro-Enterology, p . 511.

Man's natural attitude during defecation is a squatting one, such as may be observed amongst field workers or natives. Fashion, in the guise of the ordinary water closet, forbids the emptying of the lower bowel in the way Nature intended . . . It is no overstatement to say that the adoption of the squatting attitude would in itself help in no small measure to remedy the greatest physical vice of the white race, the constipation that has become a contentment. Hornibrook, The Culture of the Abdomen, p . 75.

It should be mentioned in this connection that a very common cause for unsatisfactory results . . . is improper height of the toilet seat. It is usually too high. An ideal seat would place the body in the position naturally assumed by man in primitive conditions. The seat should be low enough to bring the knees above the seat level. Williams, Personal Hygiene Applied, p. 374.

The high toilet seat may prevent complete evacuation. The natural position for defecation, assumed by primitive races, is the squatting position . . . When the thighs are pressed against the abdominal muscles in this position; the pressure within the abdomen is greatly increased, so that the rectum is more completely emptied. Our toilets are not constructed according to physiological requirements. Aaron, Our Common Ailment , p.66.

The Thailand government has had a long-established program of improving rural latrines at Chiengnai. Perhaps the most recent achievement in this area has been the development of a water-seal squat-type (squatting plate) toilet bowl that any farmer can build for less than a dollar's worth of material. The Thailand Ministry of Health sells a 2-component cast aluminum master mold from which countless numbers of units can be built. I secured a couple of these Chiengnai molds for our owes experimentation—and to loan out to people interested in building their own toilet bowls.

The finished toilet bowl is quite satisfactory. It takes about one quart of water to flush the unit—as opposed to 4 gallons for the conventional water closets. The bowl can be maintained clean and sanitary without difficulty. And most important of all, the use of this bowl necessitates a natural evacuation posture.

The use of a squatting plate suggests a re-evaluation and redesign of the complete bathroom facility. The room I propose is in effect a four-foot diameter shower stall. A single flexible water inlet—of the type commonly used in Denmark—supplies showering, lavatory washing and bowl flushing. A single drain disposes of all wash and flushing water through the bowl trap. (Ideally, a solar water heater and storage facility directly overhead supplies consistent warm water needs.) Directly below the squatting plate an excreta-disposal compartment is provided.

There are two basic methods of excreta disposal: The compost privy and the septic tank. The first process is aerobic and requires oxygen in its fermentation process of decomposition. The second is anaerobic and consists of a putrefactive breakdown—in places where oxygen does not have access. We must choose between fermentation and putrefaction in our attempt (1) to reclaim the nutrient and fertilizer value of waste, and (2) to dispose of excreta waste in a sanitary manner.

World Health Organization publications present a compelling argument against handling excreta in an anaerobic (sewage and septic tank) manner. As a result of not having oxygen in a putrifactive action, no heat build-up occurs and therefore certain pathogens and parasites are not fully destroyed. It has been found that contaminated material in liquid suspension (anaerobic digestion) can remain viable for as long as six months. For one thing, there are far more species of bacteria involved in aerobic decomposition than in anaerobic putrification.

Other problems are associated with the disposal of water-borne waste. Sewage necessarily containing large quantities of water (necessary for the transport of the excreta) is difficult to treat. Water does have a certain ability for self-purification. But this requires oxidation and usually the volume of water is too small in proportion to sewage to supply the required quantity of oxygen. Consequently the receiving water becomes foul and normal fauna (especially fish which require oxygen to live) are destroyed. The receiving water also becomes contaminated with pathogenic bacteria, protozoa, and with the eggs and larvae of harmful helminths (liver flukes).

Our society not only legalizes pollutive unsanitary disposal methods, it also outlaws an improved nutrition—an essential factor in prevention of disease—which is obtained when excreta wastes are returned to agricultural lands as plant nutrients.

The only really practical way to reclaim these wastes is through aerobic composting. Pathogenic bacteria and worm eggs can survive no longer than 30 minutes to 1 hour in a compost situation. Compost temperatures rise to 160 degrees F. High temperatures, however, are only partly responsible for this bacteria destruction; competing bacterial flora and predatory protozoa contribute as well. Aerobic composting is achieved by a wide succession of bacterial and fungal populations—each suited to its own environment and its own relative duration: The activities of one group compliment the other.

Humus is the end-product of properly composted organic materials. Humus contributes to increased nitrogen-fixation in the soil from nitrogen in the air. Also, as the gradual decomposition of insoluble organic matter takes place, nitrogen is liberated (as ammonia) and then oxidized to nitrates. Plants can utilize this nitrogen only in the form of nitrates. So when raw (not composted) wastes are spread on the land—as is commonly done in the Orient—nitrogen evaporates into the air instead of being used by plants.

The primary key to good compost-building is to establish correct proportioning and blending of the raw materials. In essence the problem is one of determining carbon and nitrogen ratios (C/N), along with the correct amount of moisture and aeration. Cellulose organic matter like straw or sawdust is rich in carbon, and excreta are rich in nitrogen. It has been found desirable to keep the C/N ratio above 30 to 1 when excreta is used; excreta should equal 10% to 25% of the total weight. Urine contains considerable larger amounts of nitrogen than do feces. Raw garbage has a C/N ratio of 25 to 1; sawdust, 511 to 1; farmyard manure; 14 to 1.

Aeration helps maintain the required high temperatures in an aerobic composting condition. Turning the compost pile at frequent intervals has been a traditional method of achieving aeration. Yet, turning adversely effects nitrogen conservation. Ammonia readily escapes to the atmosphere when the material is disturbed and exposed.

As one becomes more familiar with the whole process of aerobic composting, the design of an appropriate facility falls into place. The facility design can be likened to that of a furnace: Material (fuel) is placed in a combustion chamber; a vent stack (chimney) is provided to carry off gases that are produced from the decomposition (methane, carbon-dioxide, ammonia); and, finally, a storage compartment must be supplied for the end product (humus, or ash, in the case of a furnace).

The size of the facility depends, of course, upon the number of people using it. About 2 pounds of excreta per person per day, or 1 1/2 cubic feet per person per year, is used as a design figure.

If the initial C/N ratio is 30 to 1, it takes about 10 days composting time; a 78 to 1 ratio takes 20 days. Using the 1 to 5 volume ratio of excreta to refuse, and figuring that a family of five will produce about 1 cubic yard of partly digested excreta in four years, a compartment size of 1 cubic yard would fill in about 9 months. It must be remembered, however, that decomposition into gases and soluble materials reduces volume and mass as much as 80%.

The Indian Council of Agricultural Research at Bangalore developed extensive composting programs based on the compost privy principle.

They built an experimental "double vault" latrine. During the time that one compartment was being used, compost material in the adjacent compartment was ripening. A period of 6 months lapsed between clean-outs, This two-compartment system appears to be superior to others. However by incorporating a simple damper mechanism, only one squatting plate need be provided.

Rikard Lindstrom of Tyreso, Sweden, has patented a simple aerobic composting chamber. Its salient feature consists of a sloping (16-degree) bottom to the tank, which provides for a continual movement of the decomposed refuse to a storage chamber as additional wastes are added to the other compartment. The chamber bottom should contain a thick lays (12-inches) of straw or sawdust so that urine will be absorbed and reclaimed. This porous layer of cellulose also provides aeration to the central section of the pile. Lindstrom used a system of inverted U-shaped conduits and ventilation holes to provide adequate aeration. Air circulation is also accelerated through solar-heated flue conversion.

In Japan, where excreta is traditionally used as a fertilizer, powdered soybean is often added. Enzymes in the soybean speed up the breakdown of organic solids. Kazuyoshi Yamaji of Tokyo holds a U.S. patent on a "powdered deodorizer of the acceleration of ripening of organic fertilization fertilizers." A dried and powdered cereal containing a large quantity of enzyme is first mixed with rice-bran, barley-bran, or wheat-bran. Water is added and it is heaped for fermentation. It is then dried and powdered and mixed with tricalcium phosphate and the powder of germinated seeds of cereal such as barley, wheat, bean, etc. which contains a large quantity of enzyme. Only a small quantity of the finished product need be sprinkled on the excreta.

Bio-Dynamic gardeners use a special preparation—inocula—in making compost humus. The formula is based on the researches of the late Dr. Rudolf Steiner. One of these exotic preparations (502) is made from yarrow blossoms, fermented together with deer bladders over a period of 6 months in earth during the winter.

Using enzymes, hormones, or biocatalysts in the decomposition of organic material and for nitrogen fixation may prove to be an interesting sideline, but none of these inocula are really necessary to a properly balanced compost environment. Organic material contains all the growth factors and vitamins necessary for normal development. These growth factors are produced by micro-organisms in sufficient quantities in a mixed microbial population to meet normal growth requirements.

From the point of view of cost, health, and good design, I recommend the cylinder-shaped structure. The 4-foot diameter structure contains, in its series of levels: Effluent drainage pit, compost chamber, bathroom facility, solar water heater. A very simple slip-form jig can be employed to build the solid concrete walls. The complete unit is available from me for loan to interested people. Floor and roof are cast-in-place concrete. Ideally the unit would be built on a hillside to provide best access to the compost compartment. It can be built as a detached structure or connected to hall, breezeway or directly to sleeping unit. The accompanying drawings and photos best illustrate the structure and techniques of construction.

A widespread use of the compost privy is not to be expected. There are many social, legal, and technical difficulties associated with adopting this new functional mode of handling human excreta. For clarification on specific aspects, ask your friendly Building Inspector. In my judgement the long term personal rewards and benefits to the environment warrant whatever manner of subterfuge deemed necessary to build the compost privy. No County Building Department should have the power to prevent my squatting to relieve myself, nor should it prevent compost activities limited to my own garden.

Bibliography (Books listed in order of importance)
An Agricultural Testament; Albert Howard
Excreta Disposal;
World Health Organization
World Health Organization
The Bathroom;
Alexander Kira
Fertility From Town Wastes; Wylie