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?
Passive
Note: Cost, carbon and footprint are broad judgements against comparable building approaches, not measured figures.
A room that works as a study or play space day to day and becomes a guest room when needed, with a sofa bed or fold-away bed. Guests have somewhere to sleep without a spare room standing empty the rest of the year. The house can be smaller and cheaper to heat.
Nothing separate is built here: this is a choice about how the home is designed or used.
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The only option catalogued for this need so far, so there is nothing to compare it against.
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.