🌇 The Multifunctional Roof

About this simulation

A flat rooftop is scarce, expensive real estate. Cities increasingly ask it to do three jobs on the same square metre: generate solar power, slow down and store rainwater before it floods the storm drains, and grow a green roof that shades and cools the building beneath it. This lab tiles a model rooftop into a grid and lets you decide how much of it goes to each use, then shows the physical trade-offs in real time.

How it works

• Each tile is pre-assigned a random priority value; as you raise a slider, tiles below that threshold switch use — so the layout shifts smoothly instead of reshuffling randomly.
• Solar tiles tilt toward the sun and their glow brightens with sun elevation; output also derates on very low sun angles, like a real PV array.
• Green roof tiles soak up rain (runoff coefficient ≈0.3) instead of sending it straight to the gutter (≈0.9 for hard surfaces), and they cool the roof deck through evapotranspiration.
• Rain that isn't absorbed runs down the gutter pipe into the cistern, whose water level rises live with rainfall intensity and impervious area.

Controls

• Solar coverage — share of the roof covered by PV panels.
• Green roof coverage — share covered by planted, water-retaining roof (capped so solar + green ≤ 95%).
• Rainfall intensity — how hard it's raining, in millimetres per hour.
• Sun elevation — angle of the sun above the horizon.
• ↺ Drain cistern / reshuffle — empties the tank and re-rolls the tile lottery. Drag to rotate, scroll to zoom.

Did you know?

Real "biosolar" roofs raise panel efficiency slightly because the surrounding vegetation cools the air around the modules — PV output falls as panel temperature climbs, so a cooler roof deck is a genuine, if modest, energy bonus.