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How to Design a Passive Solar Floor Plan

Solar Passive design is one way to guarantee from day one that your house will be energy efficient and great to live in.

What I’m about to outline here is is one of the most cost effective and rewarding ways to make your house great to live in. Solar Passive Design means a higher quality living space as well as lower power bills.

This goes beyond designing your house for maximum efficiency. The aim of passive solar design is to use the sunlight create the most comfortable (thermally) and inviting (spacially) environment.

Here are the key elements:

Window sizing

Now - a few caveats. Solar design is different for each climate. This particular post is geared towards people designing their own home. And depending where you live, it may not be possible to employ every tactic explained here. However, by using some of these principles, it’s possible to create a house that works with its environment.

passive solar design

The basic rule of thumb is that in the Northern hemisphere orientate a house to the south, and in the southern hemisphere, position a house with most of the windows facing north.
The logic behind this is simple. (We’ll stick to the Northern hemisphere for this example.) During the winter, the sun moves across the sky at a lower angle. This occurs because of the tilt in the earth’s axis. During this low-sun time, the sun’s rays also strike the earth at a slant.
This means that if your windows face south, you will get winter sun coming much further into your house - exactly when you most require sunlight.

Window sizing
Windows lose a lot more heat than walls. Even double and triple glazed windows will lose more heat than walls. So window sizing is important in cooler climates. One way to look at window sizing is to take the ratio of area made up of your windows. For each climate this is different, but there is an optimal wall to window ratio. By keeping close to this ration, you can size and place your windows to get maximum sunlight during the day and not lose huge amounts of heat during the night.
Relating to orientation, you can also place windows for winter sun (south) morning sun (east) and afternoon sun (west.) One trap many people fall into is placing windows only for the view. If the view happens to be southerly, great. However in their day to day living, people gravitate towards sunlight. So placing windows for sun is equally important.

Every material has a different property. As relates to sunlight, the thermo-dynamic properties of building materials are particularly important. For instance, have you ever stood next to a stone wall at the end of a hot day? If you have, you probably would have noticed that it is still giving off heat. This is because stone has a high thermal capacity.
In other words, stone takes time to heat up, but once it is hot, it stays hot for a long time.
So how to take advantage of this in solar design? One common example is to place a large south facing window to allow sunlight onto an insulated concrete slab, tiled or paved. The idea is that the slab heats up during the day. And stays warm all night.

Shading is very important for hot climates. In summertime, the sun falls from directly overhead in the hot part of the day. Houses get slanting morning and afternoon light. This is when shading on your southern border can be useful.
The summer sun is shaded, while the winter sun comes inside the house. It’s worth looking at western windows as well, so that afternoon sun doesn’t overheat your house.

In Short
These are some basic principles of passive solar design. There are many more, and they can be applied with great effect. For starters - one very good way to get a feel for passive solar design is simply to spend a day on your house site, and observe where the sun comes from.
Then think about where you’d like to have sun inside at different times of the day. It’s not rocket science, and it’s not hi-tech. But it can make all the difference in your house to have that warm sunny feeling.