Sunday, 1 February 2015

How to: have a cool house

Much has been written in recent years about the potential for plants, particularly trees, to keep houses cool in the increasingly hot and unpleasant Australian summer heat waves. A study from Melbourne found that for every 5% loss of urban tree cover, there is a 1-2 degree increase in air temperature - quite a lot!

In a nutshell, growing trees around your house - particularly ones that provide shade to the east, north and west - will help create a microclimate that is a fair bit cooler than  areas that are paved or even covered with lawn.

Plenty of trees native to the Illawarra are well suited to this shading role. One beautiful local tree is the Bonewood (Emmenosperma alphitonioides), which has an elegant shape and masses of orange fruit in winter. I don't have any great photos of it, but this shot of the leaves by Peter Woodard on Wikipedia gives you an idea. You can also see Bonewoods growing on Gipps Road just east of the Keiraville shops.    
Slightly out of focus - seeds of a bone wood
tree growing in Gipps Road, Keiraville
The Birdlime Tree (Pisonia umbellifera) is a small rainforest tree (about 3-5m) that will grow well in part shade, and should cope well with the difficult area along the fenceline between suburban houses. It has beautiful large glossy leaves with a reddish tinge. 
Not the greatest shot - Birdlime Tree
growing in part sun on a creekside.
Shrubs that can be kept pruned, like the Lance Beard-Heath (Leucopogon lanceolatus), and (Banksia ericifolia) or the native elderberry (Sambucus australasicus) are useful for shading the difficult areas alongside westerly fences. The heath and banksia prefer sandy soil, while the elderberry is pretty flexible as long as it is not in full sun. 
This is a baby Lance Beard-heath, showing
the amazing pale green star shape of the
new leaves as they unfurl. It can grow to 3m. 
Here a Heath-Leaved Banksia more or less
completely hides two Native Elderberry
bushes. They are all thriving with about
3-4 hours sunlight a day, and just need a
periodic prune to keep them shrubby. 
See also my earlier post about local deciduous trees suitable for growing to the north of buildings, letting the low winter sun through and providing shade and protection in summer. And check out Mallee Design's post on water gums as a small shade tree. 

This section of the CSIRO's Your Home Technical Manual has a few other tips on siting trees and vines for shade, and keeping houses cool with other types of shading. 

What are you growing to provide shade in your garden? 

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