Solar Envelope Design

A solar envelope is the three-dimensional volume within which a building can be built without shadowing its neighbours during the hours that matter. It is calculated from the sun's path at the site's latitude, and it turns a vague good intention — build for passive solar — into a rule that can be drawn, measured, and enforced.

The usual application is urban, where density and daylight are in direct competition. Our interest is smaller and more local: we are laying out a barn, a workshop, and a residence on a slope, and we want the arrangement decided by the sun's winter arc rather than by what is convenient to pour first.

We mapped the sun's path for 48.2° north at the winter solstice, the equinoxes, and the summer solstice, and drew the shadow each proposed structure would cast at 9 a.m., noon, and 3 p.m. The usable south-facing ground is the constrained resource here: the orchard wants it, the greenhouse wants it, and the house cannot be allowed to take it from either.

The result is a stepped arrangement along the contour, with the tallest building at the north edge and the greenhouse at the south, and roof pitches set for the winter sun rather than the summer one.

Solar envelope design is usually taught as a planning tool for cities. It is equally a tool for a farm, where the thing being shaded is not a neighbour's window but the ground that grows your food. Drawing it first is cheaper than discovering it later.