May 2021 - My Hemp Tiny House

Pictured is my compost toilet — Tiny house outdoor compost toilet

In this post I will describe how I built a simple outside compost toilet that was used during the construction phase of the tiny house project.

I chose a compost toilet for simplicity, to save water and because my tiny house is not connected to any sewage network. You can read more about the ultra simple ‘biolitter’ toilet here.

The image to the left shows my compost toilet setup. Building it was the first job I had to do!

As you can see, it consists of a box made from OSB. The top face of the box is removable and a large galvanised steel bucket is placed inside. I had to fix more OSB inside the box to raise height of the bucket to just under the top face. The last job was to cut a hole in the top and screw on a toilet seat.

Next to the toilet was placed a plastic bucket containing the compost ‘litter’. This has a lid to keep the litter dry and keep out creepy crawlies.

In order to keep the toilet stable on the uneven ground, I placed it on another piece of OSB.

Toilet Enclosure

The toilet was placed in a pop-up shower cubicle with a zip-up door.

Pictured is a decathlon pop up shower cubicle — Pop up shower cubicle for compost toilet

I got mine from Decathlon ( a French outdoor products retailer).

The cubicle is quite handy in that it goes up very quickly and packs down into a small space. There is also a mesh pocket inside for putting shampoo, hand sanitizer etc.

I actually bought two cubicles and used the other one for the solar shower.

Each cubicle cost £49.99 which is ok. I considered building a toilet and shower enclosure from wood, but that would have cost more, taken longer and would eventually need to be dismantled and disposed of. The cubicles have been great in that they can be quickly installed and removed each time I visit the tiny house.

As the cubicle is open at the top, I used un umbrella to cover up the hole when the weather was bad. You could just as easily tie on some plastic sheet or material from an old tent.

Compost toilet litter

For the compost toilet litter, I initially bought a bale of wood shavings from a local agricultural co-op (these are very handy shops in rural France and you can buy all sorts of items: hardware, work clothing, garden items and even local food and drink).

Anyway, the wood shavings are said to be better than sawdust as there are more airspaces and so the compost is better aerated.

After each visit to the toilet we added a handful of litter and the bucket was emptied every day or two. After emptying I gave the bucket a good rinse with the garden hose, added a layer of litter and it was ready to be used again.

The wood shavings worked ok and lasted for most of the first summer (about 6 weeks). Later on I switched to using hemp as I had a large quantity left over from the tiny house build.

It turns out that hemp is well suited for use in compost toilets. I didn’t know it at the time, but hemp is also sold for use as animal bedding. One supplier claims that is is more absorbent than wood shavings or straw and is also good at reducing odours. I also learned recently that a Dutch company make public urinals that use hemp, the end result being an organic fertilizer. Apparently hemp composts quite easily.

So, hemp seems like the ideal stuff for my compost toilet and luckily I have loads of it lying around. So that’s what I will be using for quite a while!

The Compost Heap

My first compost heap was very quick, cheap and simple. I made it from reed garden screening that I screwed to 4 wooden posts hammered into the ground.

Pictured is a sketch of a compost heap — Quick and simple compost heap

The base was about 0.8m square and the height about about 1.2m.

Besides the toilet waste, I also used added food scraps, waste paper and some cardboard.

Each time I added toilet waste onto the heap, I also added a bucket of dry hemp on top.

By the end of the summer, the heap was nearly full.

Some months later I noticed that the pile of compost had shrunk a little and when I turned the top layers over, there was steam coming from the middle. So its seems that the decomposition process was working.

Bad Smells?

Yes and no.

As the toilet cubicle was open at the top and the toilet itself had a lid, it wasn’t smelly in the toilet itself. At times it was used by me, my 2 children and my 2 step-children and nobody complained!

The compost heap did produce some odours though. Absorbent as the litter is, there always seems to be some urine at the bottom of the bucket. When emptying the bucket onto the compost heap, this liquid is then at the top. Although I did add a layer of dry hemp, there still tended to be a urine odour coming from the heap. It didn’t help that the compost heap was close to the house. Putting more dry hemp on the heap reduced the smell but also filled the heap up quickly.

In future I will locate the compost heap further from the house (but not too close to the neighbours!) and will make it a bit bigger so that I can add more dry hemp.

Next steps – An Inside Toilet

The next stage of the building process is to complete the shower room inside the tiny house. Apart from the shower, it will also have a compost toilet and a wash hand basin.

My plan was to build another compost toilet, albeit a more ‘attractive’ version, something like the one shown below.

Pictured is a compost toiler — Portable Compost Toilet

However, I came across a ready made plastic camping toilet which looks worth a try.

At around £30, it’s not much more expensive than the price of a new toilet seat. It has the advantage of being less bulky than a home made ‘square box’. This could be a real bonus as the shower room is very small (little more than a cupboard). The shape looks like it would give more space for the user’s feet while sitting. It’s also a comfortable height (44.5cm). The 22 litre capacity should mean that I don’t have to empty it quite as often too.

Pictured is a plastic camping toilet — BranQ camping toilet

So I went ahead and ordered one and will try it this summer. I also ordered some compostable plastic liners for the toilet. These will help keep the toilet clean and may also reduce odours from the compost heap if it gives the hemp a bit more ‘absorbing time’ before the bag decomposes. The risk is that they don’t actually decompose very well and/or they impede the aerobic process. I guess I’ll find out soon enough!

In a previous post I dismissed the idea of a solar water heater as being too complicated and expensive.

However, it is still an appealing idea. Simple, clean, free, effective and ideally suited to make use of the sunny French climate where the the tiny house is located.

Unlike a ‘normal’ house with a ‘normal’ family, my hot water requirements are minimal. Using a Portashower, I know I only need 5 litres of water per shower. The tiny house can only sleep three people (and mostly it would be just me). So I could probably get by with 20 litres of hot water per day, or even less.

Commercial Solar Water Heater Systems

The typical solar arrangement (shown below) with a roof mounted solar panel feeding a large hot water cylinder would be way over the top for my tiny house.

Pictured is a diagram of a typical solar water heating system — Typical solar water heating system

Even a simpler ground mounted solar panel with a thermosiphon header tank is too big and too expensive. For example, this 200 litre system, from the French company Solaris, costs nearly 1300 Euros.

Pictured is a thermosiphon solar water heater — Solaris solar water heater system. Ground mounted and works on thermosiphon principle.

DIY Systems

I know that people have been making DIY solar water collectors for years. Typically these consist of copper or plastic pipes in a grid or coil arrangement, painted black and placed in a glazed insulated box. Hot water from these collectors is normally transferred to a tank – either by pump or thermosiphon.

There is plenty of information out there on DIY solar water builds, such as the one shown below from instructables.com.

Pictured is a DIY solar water heating system — DIY solar water heating system

Going down the DIY panel route has advantages. I could build something small enough to meet my needs and I wouldn’t have to pay the shipping costs of a bulky commercially available panel. But what about the header tank? I don’t need 200 litres. What are the options?

I considered lots of possibilities but the one that seemed most promising was based on an insulated plastic cool box. I could easily get one with about 20 litres capacity (perfect!) and I could probably fit a tap to drain off the hot water as needed. The problem then is that I’d then have to manually top up the panel with cold water, unless I fitted a float valve plumbed to a cold water feed. So even now things are starting to get a little bit more complicated.

Is there an even simpler way?

Pictured is a solar batch water heater — Solar batch water heater

My thoughts then turned to the old idea of the solar batch water heater. At their simplest, these are basically a “tank in the sun”. Typically they consist of a recycled water cylinder, painted black, put in a glazed and insulated box and plumbed in-line with the domestic water heater. Thus the cylinder is both the solar collector and the storage vessel. The hot water coming from the cylinder, into the domestic water system, may require some ‘topping up’ with heat to get it up to temperature, but useful energy savings can still be made.

OK, so the batch water heaters are cheap and simple, but I dont want a giant cylinder in my garden with much more water than I need.

But what if I could make a normal solar collector with a large enough water capacity that it effectively became a batch heater? I.e. no need for a separate tank.

Remember, I only need 5 litres of hot water at any one time.

With this in mind, I came up with the following design:

Mini Batch Water Heater

There is nothing revolutionary in my design. The important point is that the 22mm copper pipe is large enough to give a total water volume of 5 litres for a panel that is around 1 square metre. It might not heat up as quickly as a normal collector (which has a lower water volume) but that’s not too important. If it can get the water to 45 deg C in 30 mins or so, that will be absolutely fine.

I wont go into too much detail regarding the construction. The 22mm copper pipe would be soldered together using standard elbows and tees. Ideally it would be clipped onto a thin metal sheet of some kind in order to increase the amount of heat absorbed, but I think this is optional. The whole lot is then sprayed matt black.

The retaining frame is made from wood and insulated at the rear to reduce heat loss. I think that anything can be used for the insulator but I suspect a sheet of foam would be cheap, effective and easy to get hold of.

As for the glazing, I wouldn’t be too keen on using real glass. Besides the weight and fragility, it would also have to be custom cut. I would go for clear, corrugated polycarbonate. To avoid it fogging on the inside, I would seal the ends with tape. A bead of clear silicone would fix it into the frame.

A pressure reducing valve (PRV) might be an idea if there was any chance that high temperatures would cause water expansion and pressure on the solder joints. I guess this wouldn’t be needed if the heater was attached to a garden hose as this could expand slightly. Of course, if the garden hose was disconnected all the water would drain out! So maybe a non return valve would be a good idea, in which case the PRV might be needed after all.

Some wooden legs either side of the frame would allow the panel to face the sun at, say, 45 degrees. If I was being really clever I could make a cradle so that the panel could be rotated to any angle.

If I wanted to store a greater quantity of hot water then I could fill up an insulated container 3 or 4 times during the afternoon, giving me some for the evening.

Should the panel prove to be effective, it might actually be worth connecting it to the water system of the tiny house. It could conceivably be fixed onto one of the exterior walls of the house and hinged so it would swing outwards to collect the sun.

To conclude – solar is back! If I make it to France this summer (2021) and I finish all the other jobs I have to do, then I will have a go at making the mini batch water heater. Stay tuned to see if it works…

How I made a simple outside compost toilet.