Why do some houses feel airy, light, spacious and open while others feel dark, dingy and claustrophobic?
The difference comes down to each houses’ Solar Access.
This article will discuss why maximising Solar Access not only makes a house feel more vibrant, but is essential for true Passive Solar Design.
Note: If you haven’t already, it may be worthwhile reading Sustainable Architecture 101: Introduction before reading this article.
Sustainable Architecture Pillar 2: Solar Access
Solar Access refers to the amount of direct and diffuse solar energy a building receives and directly impacts energy use, thermal comfort and how ‘livable’ a house feels. Optimal solar access can improve thermal comfort and decrease energy requirements thus reducing greenhouse emissions.
Solar access is measured by the number of hours that the sun can shine into north-facing windows between 9am and 3pm on the shortest day of the year (22 June, mid-winter).
The ability of a house to maximise Solar Access is a key pillar in desiging a true Passive Solar House and depends upon decisions taken in the first steps of a project, some even before design begins.
The three significant factors that impact Solar Access are:
1. Site Selection
The first step in designing for Solar Access is selecting a suitable site.
In the Southern Hemisphere, maximising Solar Access means securing a property that can take advantage of the esteemed north facing light.
However, a north facing direction is by itself, no guarantee of good Solar Access.
It’s important that a site is selected that is known to be able to achieve a good level of unobstructed, north facing, winter sun (since the winter sun sits lower in the sky than the summer sun).
Any obstructions in the form of buildings, fences, trees or other features to the north, northeast or northwest can block Solar Access – note that in mid-winter obstructions cast shadows two to three times their height.
The Australian Bureau of Meteorology (BOM) generally recommends that the sun should be able to shine six hours into the windows during winter. Especially in cooler areas, the BOM also recommends solar access to east-facing windows.
2. House Orientation
The second step in designing for Solar Access is orienting the house/dwelling correctly.
An ‘ideal world’ house orientation in the Southern Hemisphere would run east west – as this maximises the proportion of building exposed to North facing light.
Living areas should be ideally orientated within the range of 15°W-20°E of true or ‘solar’ north. Good house orientation and clever use of eaves can block out harsh summer sun yet allow the lower winter sun to heat the building with zero extra costs or effort from the occupants. By contrast, poor orientation will result in heat loss in winter and will lead to overheating in summer.
3. House Floorplan
The third step in designing for Solar Access is designing the internal floorplan correctly.
The decisions over floorplan and room placement not only influence convenience and comfort but also directly impact the energy efficiency of the building.
General floorplan guidelines that promote good Solar Access and energy efficiency include ensuring that:
- Rooms with similar uses are zoned – allowing for the separation of heated and unheated rooms (thereby reducing heating/cooling needs).
- Living areas/zones are north facing eg. family rooms, kitchens and rumpus rooms.
- Windows to the west sun are avoided – especially for living rooms and bedrooms.
- Windows to the east are small, shaded in summer and oriented correctly – between 30° east of true north and 40° east of south.
- ‘Buffer zones’ are created to the west, east or south. These buffers (eg. Garages, bathrooms, storage rooms etc) can protect the building from summer sun and winter wind thus avoiding unwanted heat gain or loss
- North facing obstructions are avoided – eg. shaded courtyards, garages or other deep articulations.
- ‘Air-locks’ to external doors are incorporated – to reduce the loss of heat when external doors are opened.
- Cross ventilation is promoted by designing openable windows and doors located on different sides of the home.
- Zones that use water are grouped together to minimise heat loss from pipes, plumbing costs and water wastage.
Building Shape: Surface Area to Volume Ratio (S/V)
When considering floorplans, the Building Shape (or more specifically the Surface Area to Volume ratio, S/V) is an important factor for the performance of a building.
The greater the surface area, the greater the potential heat gain or loss through it. Consequently, a small S/V ratio implies minimum heat gain and minimum heat loss.
In order to minimise unwanted losses and gains through the fabric of a building, it’s desirable to design a compact shape, without articulation. In theory, the most compact building would be a cube however this configuration may not be acceptable for many reasons however the principle is:
“…to minimise heat loss, the building shape should be as compact as possible.”
Sustainable Architecture Solar Access: Conclusion
Why do some houses feel airy, light, spacious and open while others feel dark, dingy and claustrophobic?
The difference comes down to the Solar Access of a house.
Solar Access refers to the amount of direct and diffuse solar energy a building receives and directly impacts energy use, thermal comfort and how ‘livable’ a house feels.
The ability of a house to maximise Solar Access is a key pillar in desiging a true Passive Solar House and depends upon decisions taken in the first steps of a project, some even before design begins.
The three significant factors that impact Solar Access are:
- Site Selection
- House Orientation
- House Floorplan
The next article in this series will focus on Pillar 3 of Sustainable Architecture: Insulation.
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