I previously covered the various pros and cons of having a homemade rain barrel setup on your property in Harvest Your Own God-given Water, and as per my own advice I decided it was time to act. In this article I will be covering various angles of how I actually went about my own rain barrel installation. We have a vegetable field behind our house and being that water is something that we use a lot of to cultivate it, I decided it would be good to install a rain barrel nearby.
Water pressure increases with height, and being that a reasonable amount of water pressure is something that is kinda nice to have, I chose to place the tank up on a roof that extends out from the main structure of the house. The tank is a cubic meter, translating into a maximum weight of roughly one metric ton when full. This is a substantial amount of weight.
So although water pressure is important, a proper balance must be struck between adequate pressure, and having the tank too high up that it poses an undue structural challenge. The particular roof on which I wanted to have the rain barrel was about 3 meters up, sloped at a 19 degree angle, and wasn’t exactly what you’d consider strong. No big deal. We would simply have to beef up the structure and somehow make it work.
I proceeded to reinforce the roof from underneath on the high end, while constructing a platform that would sit level over the roof with vertical columns on the sloping end of the roof, transferring a large part of the weight directly down to the ground. This would take a large component of the weight-force off the weak roof yet still take advantage of its limited structural strength.
But being that there would still be at least half of the total weight resting on the high end of the roof, I needed to ensure it would be strong enough. There was a reasonably sturdy looking “C” channel supporting the high end of the roof from below, but was itself only supported by similar steel beams that disappeared into the wall, and spanned about two meters before reaching verticals on the other end.
The beams were sturdy, but not sturdy enough to carry the weight I was dealing with. So I installed three wooden columns underneath the steel “C” channel to reinforce the high end of the roof. This would effectively transfer the weight down to the concrete slab below, without putting undue stress on the steel beams. – Didn’t want to gamble with one ton of water 3 meters in the air.
With the platform elevated about 2.5 meters from ground level, and counting the level of the water when the tank is full, I had roughly 3.5 meters of elevation. Depending on where you live, you might use different units of pressure. Here in Japan, we use kgf/cm² or the pascal, but in the USA, psi is used. For reference, city water mains may have a water pressure of about 0.344 Mpa, 3.5 kgf/cm², or 50 psi.
- For meters and pascals, you can use: 9653Pa per vertical meter of height.
- For meters and kilogram-force-per-centimeter-square, you can use: 0.098 kgf/cm² per vertical meter of height.
- For feet and psi, you can use: 0.433 psi per vertical foot of height.
The above equations can be used to calculate hydrostatic pressure of any height. Note that overall volume has no bearing on pressure, but only vertical height from the top surface of the water to the output. This is something that people often get confused.
(To find out more about hydrostatic pressure, read my article Pressure Basics – Air and Hydrostatic.)
See Gallery for various angles of the entire project. Enjoy!