Wednesday, July 13, 2011

Passive Solar: Planting for Shade and Cooling

Planting for Shade
The idea of using plants to shading a building in summer for coolness is called passive solar and can be both practical and beautiful. In summer, sunlight during the first and last few hours of the day is a major source of building heating, so planting trees and shrubs on the east and west sides is a great way to reduce this heat buildup. Trees  provide shade during all but the middle few hours of the day. A canopy of trees with a lower level of shrubs and bushes, or a wall or fence, to block low-angled rays is most effective. If deciduous trees are selected, they will drop their leaves in fall, thereby avoiding blocking sun during the winter.

Your Crabapple LandscapExperts will use winter and summer sunrise/sunset points to determine the appropriate length and placement of tree lines for your buildings. Best is to stay a little north of the winter sun points and choose deciduous trees for the southern end of the tree line, so that some early spring and late fall sun can reach the building. Evergreen trees are also very suitable for the eastern and western sides of a building.

From an aesthetic point of view, ask Crabapple LandscapExperts for their recommendations for nearby trees. Clearing the lower trunk of branches so that winter sunlight reaches window glazing underneath the branch canopy is an option. Your LandscapExperts can provide a solar site survey to determine what height the branches should be, since the clearance height depends on both winter sun angles and the distance of the tree from the building.

Trees very close to buildings will need to have lower branches removed to above eave height. Trees further away are cleared much higher. An understory of shrubs and hedges can provide privacy if required. [See related Blog on tree clearance of valuable buildings.]

Landscaping as a Natural Air Conditioner

In summer, air brought into buildings for ventilation and air conditioning is an important aspect of passive cooling. Landscape choices can cool outside air before it gets inside, increasing the cooling effect and decreasing the amount of energy needed to reach an optimum temperature – a kind of natural air conditioning.

Plants cool air temperatures in two ways:  
● Leaves cast shade, so air beneath them is cooler because it is not warmed directly by sunlight.
● Leaves transpire moisture– release water from pores on the leaf surface – which cools relatively dry air by evaporative cooling. The US Dept of Energy  states trees can reduce air temperatures around them by up to 9°F (5°C). Directly underneath trees the cooling is even better – up to a huge 25°F (14°C) cooler.

Solutions for Passive Solar Cooling with Plants:
● Crabapple will design ventilation pathways – the pathways that air travels into a building  –  to pass through a garden belt, a mix of trees and shrubs. If space is limited, vines grown vertically on trellis or on wires can produce a similar air conditioning effect.
● Take advantage of the air-conditioning effect of plants within courtyards. The courtyard can be linked to the building it serves in such a way that the cool air from the courtyard is sucked inside.
● Water features such as small ponds or fountains further enhance cooling through evaporation. This can be especially effective in the confined area of a courtyard or entrance patio.
● Finally, consider ground covers in passive solar temperature controls. Common paving materials – asphalt, stone, brick, cement or ceramic pavers, gravel – have significant thermal mass. They accumulate heat while the sun shines, and radiate that heat back at night. Crabapple LandscapExperts choose to keep pathways and drives shaded to limit the heating of the air surrounding them. 

Investigate the benefits of Passive Solar Cooling with your Crabapple LandscapExperts Rep. 


  1. It was a very good post indeed. I thoroughly enjoyed reading it in my lunch time. Will surely come and visit this blog more often. Thanks for sharing.

    1. thank you for your comment. Crabapple appreciates your input