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?
Cool (high-reflectance) roof surface
Passive
One of 7 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 reflective covering is best decided when the roof is being replaced; the painted coating goes on an existing roof and comes off after summer, so it keeps the winter gain. Less summer gain also means less winter gain (which might be an issue in heating-dominated climates). Also watch out for local rules on permitted roof colours.
A light, reflective surface on the roof. It bounces most of the sunlight back to the sky instead of soaking it up, so less heat reaches the rooms below. It can be a home-made white coating, painted on an existing roof for the summer and washed off after it, which is the version rated here; or a reflective covering chosen when the roof is replaced anyway, which costs nothing extra and lasts as long as the roof.
The painted coating lasts a summer: heavy rain can wash it off, and it is cleaned off afterwards. A reflective covering lasts as long as the roof, its reflectance dropping as it weathers and collects dirt, most of it in the first years
Levels are relative to the other options for this need, not absolute. Fewer dots is lighter.
Cool (high-reflectance) roof surface (This page) Can I use it? Not in a flat · No rebuilding needed What does it cost me? Upfront cost: Low · Skill to build: Basic · Upkeep: Light · Change to daily life: Occasional · Works without the grid: Yes Choose it if you want cooler rooms under a sunny roof, from a coating you can make yourself and wash off before winter.
Fixed horizontal overhangs (south) Can I use it? Works in a flat · No rebuilding needed What does it cost me? Upfront cost: Low · Skill to build: None · Upkeep: None · Change to daily life: None · Works without the grid: Yes Choose it if you want south windows shaded in summer and sunny in winter, with nothing to adjust.
Adjustable brise-soleil / shutters (east-west) Can I use it? Works in a flat · No rebuilding needed What does it cost me? Upfront cost: Medium · Skill to build: Basic · Upkeep: Regular · Change to daily life: Daily · Works without the grid: Yes Choose it if you want to stop the low morning or evening sun on east and west windows.
Deciduous vegetation shading Can I use it? Not 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 summer shade and winter sun that cost nothing and grow by themselves.
DIY shade-sail window screen 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: Occasional · Works without the grid: Yes Choose it if you want the cheapest outside shade for a window, sewn yourself.
Attic radiant barrier Can I use it? Not in a flat · No rebuilding needed What does it cost me? Upfront cost: Low · Skill to build: Basic · Upkeep: None · Change to daily life: None · Works without the grid: Yes Choose it if you want a cooler top floor for the price of a foil under the roof.
Vented roof / attic assembly Can I use it? Works in a flat · No rebuilding needed What does it cost me? Upfront cost: Low · Skill to build: Intermediate · Upkeep: Light · Change to daily life: None · Works without the grid: Yes Choose it if you want the roof space to shed its heat and its damp, and the timbers to stay dry.
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.