Lowtech Graph lists low-tech options for every need of a home. Here you can compare them, find tutorials to build them, and link them together into a circular system. Why low-tech?
Water-based thermal mass (drum / water wall)
Passive
One of 2 ways to meet this need. Cost, carbon, footprint and rankings are relative to other solutions for the same need, not absolute.
What your site needs
A sealed, leak-proof, structurally adequate location (water thermal mass is heavy)
Barrels or tanks of water placed where the sun reaches them, often against a south window. Water soaks up a lot of heat during the day and gives it back slowly at night. It keeps rooms warmer after dark, more than the same volume of stone would, but the containers must never leak.
Levels are relative to the other options for this need, not absolute. Fewer dots is lighter.
Water-based thermal mass (drum / water wall) (This page) Can I use it? Works in a flat · No rebuilding needed What does it cost me? Upfront cost: Low · Skill to build: Basic · Upkeep: Light · Change to daily life: None · Works without the grid: Yes Choose it if you want to add heat storage to an existing sunny room, cheaply.
Exposed thermal mass (masonry, rammed earth, slab) Can I use it? Works in a flat · No rebuilding needed What does it cost me? Upfront cost: Medium · Skill to build: None · Upkeep: None · Change to daily life: None · Works without the grid: Yes Choose it if you are building with heavy materials and want them to smooth out the day’s temperature swings.
We don’t list sizing or quantities, as the yield of each technique depends on the quality of its build. The catalogue compares options but doesn’t dimension them. Regulatory notes are indicative, with a French example, and need to be confirmed locally.