The Strine Solar Butterfly – Can planting help lower heating and cooling costs?

A beautiful and healthy living environment includes the garden as well the home. Landscaping can be much more than something to look at and when designed sensitively can help heat and cool a building.

Over the years Ric Butt has perfected the Strine Solar Butterfly, a guide for planting for best performance in passive solar homes. The landscaping is a critical part of the overall design of any Strine project, not only working to cool and filter the air and reduce wind velocity, but also provides protected areas for indoor and outdoor living all year round.

Strine’s Solar Butterfly diagram follows the sun’s winter path guiding the height of planting to use to ensure the best winter solar access, the primary form of winter heating in an energy efficient house. The Solar Butterfly to the north is most effective when used in addition to measures taken to protect all other sides of the building as well. The right type of landscaping can provide sun protection to the eastern and western walls in summer and protection from wind-chill and wind heating impacts to the eastern, southern and western walls, all of which can affect the internal temperature of the home.

The path of the sun is very different in winter to the path taken in summer. Landscaping to the north must be designed to maximise winter sun penetration which means that plants need to be low when close to the building getting progressively higher the further away they are from the building. As the winter sun rises low to the northeast and sets low in the northwest, the landscaping to the northeast and northwest of any glazing should be very low. A well designed house in Canberra will have minimum permanent shading to the northern side, just enough to restrict sun penetration for the months of December and January. It’s tempting to think that deciduous plants are the answer to optimum northern solar access, but they are not all deciduous at the same time. Having deciduous plants that lose their leaves by mid-April and gain them in mid-October is the ideal for Canberra. There are not actually many species that do this.

Shading

Energy  efficient houses need seasonal shading and additional shading can be provided using temporary ‘adjustable’ shade devices to the north, usually a slim pergola with steel wires (cables) and deciduous grape vines. Strine recommends grapevines , as only grapes gain their leaves early enough to start the early sun shading necessary for summer in October / November, losing leaves early enough to allow maximum sun penetration in winter. Most other species of vines lose their leaves much later reducing the benefit of late autumn sun flooding the interior of a well-designed house with heat. Other vines often don’t gain their leaves until December when houses are already overheating.

After many years of listening to client feedback, our advice is that the best suited plant for pergolas is a grape vine and in particular the White Sultana. The White Sultana is perfect for the intricate northern pergola summer shading recommended for Strine houses; they are fast growing and have dense foliage for summer shading of the full glazing to the northern side of our houses. The timing of leaf growth and loss has substantial effects on the heating and cooling of passive solar homes. We use steel pergolas to minimise maintenance issues.

Evergreen (non – deciduous) plants can be part of the answer and can provide sun and wind protection to the eastern, western and southern sides of a building. Planting as shading to eastern and western walls can reduce temperatures by five to ten degrees. Wind protection also reduces wind chill and wind heat by around ten degrees on eastern, southern and western walls. Bio walls or mesh with climbing plants can be used. There are no height or width restrictions for planting to these sides, only aesthetics and views to consider.

Solar Diagrams

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