Last Updated: 13 Mar 2017

   Dry Toilets

      Basic Structure


Topics Covered

On-Site Constructed Units

Here are other pages giving further details of site-built units:

You may want to jump to one of these related pages:
⇩          ⇩
Why the Dry Toilet? Pros and cons discussed.

Site-Built Units Start with some explanations and decisions.

Fittings toilets, urinals, plumbing, containers, vent pipe, and other fittings.

Sanitation, nutrient cycle, re-use, composting, maintenance, and other long-term concerns.


To plan the basic structure you must already have made decisions (in Site-Built Units) about whether more than one toilet will be included in the structure, whether you will have a urine-diverting dry toilet (UDDT), and whether you will have a single-vault or double-vault design.

Toilet Shelter and Superstructure: 

stairs For an outdoor or stand-alone unit, the toilet superstructure forms the toilet compartment, providing privacy and comfort for the users.  Most often, because the vaults containing excreta are built above ground, stairs are required to enter the compartment or cabin (or if the cabin is at or near ground level, steps inside just in front of the toilet will be needed)
(Photo: WECF)

However, where soil conditions allow, and with suitably slanted or filled terrain, you could excavate and construct the vaults fully or partially below ground, reducing or eliminating stairs that users must climb.
(Photo: SSA)
slanting grade

Choice of Location:  Situating the toilet structure to maximize sun warming of vault doors and vent pipe is desirable. Although underground vaults or partially underground placement can sometimes be an option (as just mentioned above), it is best to build vaults with floor at least 10 cm (4”) above ground level and not placed in depressions or at low points in terrain. This avoids flooding or collection of rain water, and assures easy access. The floor of the vault should be slightly sloped to allow any toilet seepage to drain into a soaking area. Due to the dry condition of the feces, leaching of pathogens into ground water is negligible so the floor need not be sealed.

Units Within or Adjoining Houses or Other Buildings:   Those who are transitioning from pit latrines, with their foul smell, at first prefer dry toilets to be built at a distance from their dwelling.  Once they realize how little odor comes from a dry toilet, if given the chance, they prefer new ones be built conveniently close to the dwelling or adjoining it.  Some will partition off part of their dwelling as a lavatory or bathroom to house the dry toilet (see photo).

← Dry toilet attached to existing building, entered from outside.  It appears to be single vault design; note access door at bottom.
(Photo: WECF)

attached ← Attached unit entered from inside home.  Note access doors to double vaults.
(Photo: WECF)

Base of Structure:  Assuming a structure built above ground, the stability of soil is important. 

If soil is stable, compacted, well drained and not absorbing excessive water, then a wooden structure might be mounted on concrete blocks that are set on gravel.
(Photo: DTS)
blocks  Concrete blocks set in gravel at corners of wooden single-vault toilet structure.

If soil stability is not assured (sandy, easily disturbed, poor drainage, muddy) then a better method is to dig footer trenches and build a form suitable to hold poured concrete.

Digging footer for double vault.
(Photo: WECF)
Wooden form for footer.
(Photo: WECF)
Rocks set in bottom of footer trenches.
(Photo: WECF)
Concrete base poured.
(Photo: WECF)

The image of the plan, below, for a single vault wooden unit can be enlarged and dimensions can be read from it.

concrete base w pipe
Concrete bases for multiple wooden single vault units, each with urine drain roughed in, and J-bolts to hold wooden base.
(Photo: DTS)
Plan for wooden base upon which a wooden single vault unit will be built. Zoom in on this image for dimensions.
(Photo: DTS)

Feces Collection Vaults Or Bin Housings:
The dehydration vaults are enclosed, waterproof spaces into which the feces fall directly, or alternatively, into bins, barrels or large plastic containers located in the enclosed spaces (see Fittings).  Bins that are shorter and wider will promote dehydration better than tall, narrow ones. They have four basic functions: (1) to carry the weight load of user(s) and the toilet compartment or cabin, (2) to keep humans and animals away from the feces, (3) to afford a dry, ventilated and odor-dispersing environment, and (4) as a place for storage, dehumidification and pathogen-reduction to occur for up to one year before removal.

Odor control for the feces vault is provided by (a) the dry conditions in the vault, (b) the use of dry covering or bulking material (desiccant) added after each defecation and (c) a well designed ventilation system (see Fittings); no kitchen waste, fiber or paper products or other debris should go in.

Building Materials.  These range from bricks and concrete to light-weight structures made from timber, bamboo and other strong materials.  Most of the photos so far show base and vaults made of concrete or bricks.  But details of wood-built bases and vaults (including wood-built cabins) will be seen below.

Dimensions and Capacity.  Double vault units have two vaults, each ideally large enough to accept approximately one year’s accumulation. At the end of that time one toilet hole of a double vault unit is capped from above and the seat moved to an alternate hole over the second vault. The double-vault design makes it unnecessary for anyone to deal with feces that have not dried and detoxified for an extended period of time, making them especially inoffensive.

Consider the volume required in a vault to be approximately 0.5 – 1.0 cubic meter. Variations depend on whether one or more movable bins of a certain size are to be accommodated. For intermittent use, and where bins are used that are necessarily smaller than the volume of the vault, calculation may be difficult and experience will be the only guide.

Space also must be available for the urine container either inside the vault or a nearby external location (described in Fittings).

Vault Bases:  Bases made entirely of masonry or concrete involve more complex forms for the concrete or, alternatively, concrete block construction.  Excavation of earth can be minimal for these units - enough to form a footing for the structure, with earth tamped down and fine gravel compressed into the surface.  Images show double vault units.  For single vault unit you could change these examples to have only one vault, being sure that removable container will fit in vault interior space.  (Some designs give space for two containers so a full one may continue to dry inside vault ("resting") while a new one is filling.)

Plan for double vault toilet base, upon which cabin or compartment will be built.  Note urine drain pipes going to urine container or soak hole (not shown).  Zoom in to read dimensions.
(Photo: GIZ)
brick base
Drawing of concrete block base for double vault unit showing vault doors.  Note grate just above floor of vaults because this unit is not urine diversion, so vaults must be drained (drain not shown).  If UD toilet seats were used, and urine container included, the grate could be eliminated.
(Photo: SSA)
concrete base
Brick and concrete base complete for partially below-ground double vault unit.  Vault openings, vent pipes and urine pipe shown, vault doors on far side.  Concrete top with openings is probably precast.
(Photo: GIZ)
cinderblock base
Concrete block double vault unit, vault openings shown.  Toilet bench or pedestal will go on top of openings.  Concrete top is probably cast on site.
(Photo: SSA)

Vault Doors:  Exterior doors to vaults should be solid, well-fitted against rain and light that attracts insects and makes feces more visible when using the toilet.  Doors exposed to the sun and made of steel or aluminum can transfer more heat to the interior of the vault.  Locks or secure latches will keep out children and animals.

The Compartment or Cabin in which the toilet is placed should be made of readily available building materials.  The floor and the bench or pedestal supporting the toilet seat should be made of material with a surface that is easy to clean.  The floor should be provided with some kind of drainage that allows any wash water or rain that gets inside to exit without entering the feces vault. The toilet pedestal or bench should be properly sealed where it meets the floor, so the interior can be washed while avoiding entry of water into the vault. The cabin space should be well ventilated with screened windows or louvers.

Space must be adequate not only for toilet and urinal (see Fittings).  Distance from the toilet seat to the walls would be a minimum of 30 cm (12”) (rear and sides; two to three times this from toilet seat to forward wall or door) and overall dimensions at least 90 by 120 cm (35 by 47”).  Larger dimensions will afford greater comfort to users, space for a wall-mounted urinal and for hooks to hang outerwear and to store materials, etc.

A basket or container of desiccant (dry, carbon-rich bulking material) scooped into the feces hole after use also requires some space, as does a general trash basket. If the toilet is of double-vault design, more width is required.

For a unit built into an existing building the dimensions used by local custom or building codes must be observed, and additional space provided if sinks, showers or other bathroom amenities are included (see interior examples in Fittings).

section plan
Depending on average height of user population, the door may be low, and bench may be high.  Feces vault or container is presumably beyond urine container.
(Photo: SSA)
plan photo
Where lumber is not locally available bricks or blocks will be the desired building materials.  Note slanted vault door heated by sun.
(Photo: GIZ)
wood on brick
Bricks make a solid foundation but this UDDT structure could have been made entirely from wood, assuming plastic feces container is used.
(Photo: WECF)

Photos show a variety of configurations and construction methods for UDDTs where vaults are above ground (the most common method).

wood on brick
Double vault UDDT with simple wood framing.
(Photo: SSA)
two unit
Plan for two double vault UDDTs separated by washing area.
(Photo: GIZ)
Plans for double vault UDDT built entirely with wood set on concrete pad.
(Photo: MTU)

Below are four images of plans for an all-wood, single vault UDDT structure with more detail included.

Plans for single vault UDDT.
vertical framing
         Framing (zoom in to read dimensions) for single vault UDDT made entirely from wood.
    (Photos: DTS)
More detail of wooden single vault UDDT with bench frame in place.
rear enclosed
Rear view of single vault UDDT showing access door.

More detail and description of this all-wood UDDT project is available here.
An alternative version is available here.

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