Shade Trees

In the warm season a deciduous canopy stops sunlight before it reaches the wall or roof behind it; in the cold season, once the leaves have fallen, the bare branches let most of that sun through to the same surface. Planted close to a building the effect is measured rather than merely pleasant: shaded wood siding has been recorded about 9 C (16 F) cooler than unshaded siding in early summer, and cooling energy cut by half or more - more than a vine trained on the wall achieves.

Where to put it is the one question good sources answer differently. One gives the west side first priority, because that is where the heaviest heat of the day lands, and puts effective shading within 9 to 15 m (30 to 50 ft) of the building; another spreads the canopy right across the side the midday sun comes from, sized against how high that sun stands in summer. Either is defensible and the site decides. The winter side is a real cost: bare branches still block more than a third of the light behind them, and a dense canopy pressed against a wall has been estimated to raise winter heating need by about a tenth - though a planting that also breaks the wind can save more than it costs.

The hard part is that it is slow to arrive and permanent once it has. A canopy big enough to shade a building takes about a decade, which is why a fast short-lived tree is sometimes planted as a stand-in while a better one grows behind it, and why every conflict has to be settled at planting: the remedy at maturity is felling something ten years old. A roof-mounted solar array wants the same sunny aspect, and shading even a tenth of an array can halve its output, so a tree planted clear of one in year one can reach it by year eight. Overhead and buried services set the other limit, measured against the tree's mature height and spread rather than the sapling in the hole. After that the work is small: formative pruning while the tree is reachable, watering through the first years, a look for dead or hanging limbs on the building side, and leaves kept out of gutters and off any array below.