RC made a request for drawings/diagrams. I hope you'll forgive me, but I'm going to pass on that. For one thing, I don't have any already made up- and making them would be quite a lot of work. For another- I'm a little bit opposed to the idea of "recipes" for this kind of thing. I think they can stop people from thinking for themselves, and a Potty House is exactly the kind of project where you MUST do a lot of thinking- about your specific site, specific climates, and specific needs. (RC, it's not you I'm worried about- but other folks who will read this blog and get ideas. If you need evidence, you can take a look at some of the advice Colin is getting on "refrigeration" - cold milk?. Wow.)
So; I'd rather stick with design principles here. There are still a couple we haven't touched on, though most design stuff is outlined in the two previous posts basics and the one with pics, more, and Pics.
Looking at the pics, I can quickly see a couple aspects of our potty house you might well want to NOT copy- not because they don't work, but because they're pretty specific for our situation.
One is- all the glass on the south of the building. It's "frosted" glass, so you can't see through it (privacy being important to some people). It's certainly more work to install, and more expensive, than just putting in a wall. We need it here, for winter sun/heat. We're far enough north that the sun's angle changes hugely from winter to summer; RC, who lives in PR, has got very different sunlight parameters to deal with. Our Potty House is also IN the woods; under a couple big oak trees. Lots of shade in the summer- which is good for not frying anyone who needs to use it in the middle of the day- but you do need SOME solar heat gain in order to dry the pits. Finding the balance can be tricky.
For this particular building, probably 90% of our solar heat in the winter comes in through the south wall windows. Partly because of the low angle of the sun- but also because of the snow. Most of the time in winter there will be snow on the roof- plenty enough to prevent much light getting through that way. Luckily- when there is snow on the ground- we get a LOT more heat in through the south wall- from sun bouncing off the snow field. It's quite significant, and yes, I did figure on that before building.
2nd design aspect you may not want- you can see the roof is made of 2 different materials- part of it is asphalt shingle; part of it is corrugated translucent fiberglas. The junction is a pain in the neck; and prone to leaking, particularly during snow melt. We mostly wound up with it this way because I wanted the "turbine" "powered" air vent to go straight up, and out- and fitting an 18" pipe through the fiberglas would have been beyond my construction skills at the time. I find myself calling this air-duct/pipe the "stack", as in smokestack.
Other considerations about that roof- I wanted a substantial overhang over the entry door, because people have to use it in the rain; nicer to have a little cover while you negotiate the wet, slippery stones walkway, etc. So I opted for a frame roof there.
Why did I want a straight stack? Because bends in very low air-pressure ducts REALLY cut down on the air flow. And- the stack, you recall, is connected down into the pits, to pull wet stinky air out of the building. Using ambient wind- which is known to be uncertain. I really wanted to do everything I could to make the air flow easier- for example, the stack outside of the house is painted flat black- to absorb more solar heat, and heat the air in the stack further, making it "draw" better. (The paint is 20 years old; still looks black when it's wet, anyway.)
I'll toss out a general "sustainable -green" design principle here, which I have not seen formulated anywhere, but which I have come to completely believe in. If you are incorporating some feature which relies on a "passive" process- i.e.. it relies on physics or meteorology to work, not an electric motor- get the best advice you can on "how big" that passive feature should be- then build it twice that big. Three times bigger, if you can afford it.
"Passive" is great- and free. IF it works. And it's just in the nature of passive phenomena; like warm but not hot air rising up a chimney; that a LOT of the time, they WON'T work, if the least little thing goes wrong. Like a stray wind gust blowing down the stack, and stopping a slight air flow. Making passive features bigger gives the physics that's supposed to drive them much better odds of actually grabbing hold.
Ok, I expect to see that cited as "Greenpa's Aggressive Passive Design Principle" from now on.
Anyway- rather than build that complex roof, it might be easier/cheaper to just lead the stack out through a wall, and put a bend in it. It might also be smart to go with "active" design in a warm climate; like investing in a little solar powered fan, to really pull the air through and out. A little pricey, but nice; and the turbine, incidentally, does NOT pull air nearly as well as they like you to think; testing shows it works about as well as a ... hole in the roof. But it does keep the rain out.
Here is a major design concern we haven't touched on yet- bugs- and spiders- WILL get into the building, and into the stack. You need to design the stack so it's easy to clean out, once a year anyway- otherwise spider webs (and other webs) will build up in it to the point where you have no air flow; and everything will quit working.
It's not that you can't clean a stack with bends in it; but it sure is more difficult, and the bends invite webs.
Bugs. You need to build your potty house with bugs in mind- every step of the way. (And mice; etc.)
Big piles of poop attract lots of bugs/critters, and you really would rather not have them in the potty house with you.
A) Build the building TIGHT. Remember that a mouse can squeeze through a 1/8" crack; and little bugs through cracks smaller than that. Don't leave cracks- allow for shrinkage and movement- and caulk whatever you can't close.
B) Build everything so it can be CLEANED. No matter how tight you make it; bugs/critters WILL get in (just not so freely). They'll come in the door, with you; even mice, who will sneak in past your feet at night. (Really.) So just keep muttering "I didn't want to be the only species on the planet, anyway.", and put things together so they can also be taken apart and cleaned out from time to time.
For example- the stack not only needs to be opened and "swept" once a year- I also put in an insect screen, to keep flies from just zooming down into the pits. The screen gets dirty/webby much faster than the stack as a whole; so make life easier on yourself and design it for easy access.
Now. Here we get into a difficult area for me. I have to confess something.
I didn't INTEND to tell you all a fib- but I did. I just forgot. My "green practices" list brags "no pesticides; EVER..." My confession- I do use some "fly spray" in the outhouse; probably about 5 times a year. Flies love poop. They will get in. You have to do something about them, or you'll got completely crazy. Ick. And while I'm confessing- we do use some of the same fly spray in the greenhouse, to control fungus gnats, which are lethal for us. The spray we use we buy at the farm store- it's designed and sold to control flies in "the milk room" and around dairy cows; pyrethrin based stuff.
I'd rather not use it- but so far it's the only realistic solution. If you're going to have a composting toilet, you've got to control flies. A couple of sprays of pyrethrin down into the pit when they appear inside usually stops them for a good month. It's not easy for them to get in; due to construction- but it will happen if people insist on opening doors.
Which gets us to the last point for today- the windows do NOT open- any of them. You DO need some ventilation options, however. No matter how well you balance things, you'll find yourself with days when it's just darn hot inside, and you wish it weren't. I made our windows unopenable mostly to simplify construction- and it also makes it easier to make the building fly-tight. And it's better for SEEING , and easier to clean- you don't have big insect screen areas constantly in front of your glass, and getting dirty. What we have instead are two screened "portholes" right up in the peak of the building, under the eaves. A much better place for ventilation, since that's where the hot air goes, and glass would be pointless, since nobody is tall enough to see out right there. The portholes have hinged wooden shutters that work from the inside; so if it's too hot, or two chilly, you can just reach up and change the amount of heat that's escaping or being retained in the main room.
We'll have a summing up post next; then on to the next subject. What have I left out?