Orientation / South Facing Windows

Passive solar houses typically have windows on the southern side of the building.

Based on the movements of the sun, passive solar buildings typically have windows (glazing) on the southern facing side* of the building in order to absorb the sun’s heat energy to warm a building during the winter.  In order to stay cool in the summer, passive solar houses rely on a system of shading (or an overhang) to keep the building cool.

Simply by building in this way, a house can reduce its heating and cooling costs by 85%.

See how the house pictured on the right achieves Net-Zero Energy.

*In the northern hemisphere, in order to face the sun and obtain maximum solar gain, the windows would face the south. In the southern hemisphere, however, it is opposite, with the windows facing the north in order to maximize solar gain.

Seasonal Window Considerations

The diagram shows how the low winter sun can enter the building, while the high summer sun can not.


The diagram to the left shows how the sun is lower in the winter, while it is much higher in the summer.  (See the building at Zion National Park.)  During the day, the low winter sun can shine through windows are to allow heat energy to be absorbed into the building’s thermal mass.

While windows allow heat into a building to be absorbed, their thin and transparent nature also allows heat to escape a building.

In order to keep this from happening in cold climates, it is recommended that the glass panes are doubled (double glazing) or even tripled. An insulated window covering or thick shade can also be used to help insulate the windows and help keep the heat in the building after the sun goes down.


In the summer, as temperatures rise, a passive solar building uses its thermal mass to help keep the building cool. In order for this to happen, the summer sun is kept from reaching the thermal mass of the building.

The summer sun’s path aides in this process by traveling high in the summer sky, thus a proper overhang or other type of system is needed to shade or cover the widow, in the summer so that the sun’s heat energy is blocked or avoided when it is desired to have the building cooler than the outside temperature.

A properly designed overhang keeps the heat and energy from being absorbed into the house in the summer. (In the picture at the very top of this post, you may also notice that the overhang is keeping the high summer sun from entering the house.)

Building Orientation

Because the sun rises in the east and sets in the west, the side of the building that is utilized for solar gain needs to be facing the south to take maximum advantage of the sun’s potential energy.  If the building’s axis is located on the east-west direction with its longest dimension facing the south, more of the building is situated to absorb the sun’s heat energy.

If the building in the middle were longer, stretching toward the two houses located on either side of it, more of its mass would be ideally situated to absorb and radiate heat in the winter

Passive solar buildings are typically rectangular with the long side of the building facing south.  The distance from the source of incoming heat (south) to where it is absorbed (typically a northern wall) should be minimized. The resulting shape is a rectangle.  This is one of the lessons learned in the construction of this Off Grid Passive Solar Earthship-Style Home.

South Facing Windows and Orientation

It is ideal to have the windows (solar glazing) within 5 degrees of true south. However, windows that are within 15 degrees of true south are said to function almost as well.

As the degree difference from true south expands, the overall potential solar efficiency of the structure decreases. Put another way, the greater the degree variation from true south, will decrease the amount of the the building’s solar gain. As a result, larger amounts of supplementary energy may be needed to heat the building in the winter. As the building’s glass (glazing) faces more to the southwest, more energy may be needed for summer cooling.

Passive solar buildings typically have many windows facing the south

Southern facing windows (southern solar glazing) are a vital component for a passive solar design and building. Because the southern side of the building is the side that will potentially receive sunlight throughout the day, most passive solar buildings will feature glass dominating the southern side. Southern facing glass allows the sun’s energy to be absorbed and distributed through the building’s thermal mass.

You may hear people referring to glass as glazing. Glazing is the fancy architectural word typically used for southern facing glass that has the capacity to transfer the sun’s energy.

Another benefit of having windows on the south side, is that it allows natural light to bathe the house throughout the day. This aspect can also lower energy use throughout the house since it minimizes the use of artificial light.

All of these factors can be used to one’s advantage, depending upon the site location and depending on the specific characteristics that you want within the house.

While southern facing windows (glazing) are a necessary component of passive solar design, care must be taken to insulate them in the winter after the sun goes down, as well as shade them in the summer.

world equator diagram showing the northern and southern hemispheres

The northern hemisphere is highlighted in yellow. The southern hemisphere is white.

Note that because the Earth is a sphere, depending on where you are located, the sun will interact slightly differently than in other places.  For example, the angle of the summer and winter sun will be different.

If, however, you are located in the Southern Hemisphere, in order to build a passive or active solar home, the building will need to be oriented to the north.

Here’s a little more information about solar building in the southern hemisphere.

Vertical and Angled Glass (Glazing)

Most glass that is used in building is vertical.  Angled glass, however, is frequently used in passive solar design because it increases the amount of solar energy that can be absorbed. Caution! This can cause overheating in the summertime.

*This information pertaining to facing windows to the south works for those in the northern hemisphere. Down under, in order to use solar gain, they need to face the windows to the north.

72 Responses to Orientation / South Facing Windows

  1. Aaron February 27, 2017 at 3:21 am

    Keya, thanks for this article. I’m wondering: to what extent is *direct* sunlight responsible for over-heating south oriented homes in the summer, vs. simply the fact that there is hot air outside?

    We live in Texas. So cold-ish in the winter, very hot in the summer. Our home has a beautiful garden on the southern side of the house. The living room has no windows, but if it did it would look out onto that garden. We’d like to put in a patio/sliding door on that wall so we can look out onto the garden.

    Right now there is already an overhang on that side of the wall that jets out quite far, so that wall doesn’t really even get much direct light even in the winter. Also we have several big trees that shade the area.

    So I’m wondering: if we open the wall and put in a patio/sliding door, as long as the glass doesn’t get any *direct* sunlight in the summer, will it not heat up the room?

    Even triple-glazed glass is worse than a wall for keeping the cool air inside, right? And even if the overhang/trees prevent *direct* sunlight from entering the glass, the fact that there is simply 95 degree air on the other side of the door would be enough to make the room more difficult to cool, right?

    From reading this article and your responses to some questions here, I get the impression that as long as the overhang prevents *direct* sunlight from entering a room via windows, it won’t heat it up. So even if it is 95-100 degrees outside, as long as no light enters directly through windows, that hot air won’t make the room hotter?


  2. James Stufano March 8, 2017 at 9:43 pm

    Is there a passive solar design where the north, non-sun side has mountain views to take advantage of which are located on the exact opposite sunny south side? I guess we could do smaller windows on the north and maybe put a porch or upper deck.

  3. Marcin March 16, 2017 at 6:15 pm

    I am looking for specific data about the angle of face glazing. It depends of sun position in winter time = latitude (geographical location). For my latitude (north hemisphere 50 ° 50`40“ N and 19 °14`17“ E) that maybe 50-70 ° angle of face glazing. What is the exact value? If I remember well in winter sun should hit the glass at 90 ° to give the best effects of heating. If anyone knows some web with that information or calculator based on latitudes data, please let me know.

  4. Keya Lea April 4, 2017 at 9:55 pm

    In regard to what is worse, a wall or triple-paned (or glazed?) glass, it all depends on the insulating properties of the materials used. Typically glass has less insulating properties than a wall, but there are many different ways to build a wall.

    Passive solar building works with the integration of different materials, so typically, the house has southern facing windows and an overhang is also built with thermal mass that slows heats up and slowly releases stored heat. In the summer, the concrete/adobe/stone floor stays cool if direct sunlight does not hit it. If the inside of the house does not have thermal mass, then the transfer of heat through the air is more of a factor. In a passive solar house, the integration of the elements (including air flow – as hot air rises) heats and cools homes.

    Many of the homes here are built in Colorado, where the summers get to be 90 – 100 degrees, and many of these homes have only double paned windows, but with the integration of other materials and passive solar design, they stay cool in the summer.

  5. Keya Lea April 4, 2017 at 9:58 pm

    Yes, exactly. It requires more creative design, than the usual, but it can be done.

  6. Yen May 24, 2017 at 10:10 pm

    I’m from Vietnam. Vietnam is on the Northern hemisphere but the location is very near the the equator. So, does the south facing windows is specifically different with other sides?

    Thank you!

  7. Keya Lea June 3, 2017 at 5:12 pm

    Hi Yen!
    It depends on what you’re wanting to do. Typically homes in more temperate weather locations that have 4 seasons have a need to warm in the winter and cool in the summer. People who live / build in warmer, more tropical climates will have a different solar pattern through the seasons, while it still will be predictable, so placing windows in certain locations will have a heating or cooling effect.

  8. Meli October 28, 2017 at 8:13 pm

    Does sunlight hitting roof and side of apartment still raise temp inside if there’s no window?

  9. Keya Lea November 27, 2017 at 5:16 pm

    Yes, absolutely. If there isn’t insulation, heat will be transferred from the outside to the inside, regardless of what it’s hitting. Typically windows are seen as the opposite of insulation, which is why heat is transferred through windows more easily. Heat can also be the roof or walls if they are not well insulated.

  10. Tigger January 30, 2018 at 2:42 am

    Hi, Keya: Thanks for providing this article. I wonder how to correct/improve the air quality in a passive solar building and how to cool the house without an A/C.

    Our home is constantly at high temperature (winter: 77F @ noon and Summer 85F @ noon) because of the direct sunlight coming through our south facing windows/glasses (floor to ceiling). When the sun sets and outside temp drops significantly, the inside still remains pretty warm and temp did not drop by a lot. It’s as if the house is so well insulated that there is no vent and the hot air is standing still.

    Only when we open many doors/windows to let the air flow for a long while, we will then cool the house a bit. Then, we’d feel like we live in an open space and not in a house. It’s not practical.

    Any advice on what we can do to cool the newly built house and evenly distribute the heat throughout the house? Who can we work with to make it a comfortable living in the house all year long?

    Thanks in advance

  11. Keya Lea March 27, 2018 at 5:56 pm

    Many passive solar houses build airflow into the house, sometimes this type of building is referred to as an “envelope house”. A passive solar build that incorporated this is this transition from a former farmhouse into a passive solar one. It’s broken into two parts, so here’s the second part.

    A lot of passive solar builds also incorporate clerestory windows that open and close near the top of the house. Because warm air rises, the clerestory windows allow the heat to easily escape out of the house, and can be closed when the house reaches a temperature that the occupants determine.

  12. Dave Puig January 21, 2019 at 11:36 am

    Hello There
    I am a builder in Wisconsin and I am trying to situate a house to fit the landscape best but also to maximize solar gain. I know that south facing wall and windows is best. However, I am considering this idea. A house that is oriented so that a corner is facing due south and therefore it has a lot more wall surface that is facing south, just not due south. So there would be glass that is getting southeast sun and southwest sun and all of them would be getting due south sun at an angle. I know this is not as efficient but I am wondering if that might be cancelled out due to the fact that you would have a lot more surface area of wall and windows facing some version of south? Does this make sense?
    Thanks so much for you thoughts.

  13. Rosalind Williams April 15, 2019 at 4:16 pm

    Why would someone want a north facing home in terms of energy efficiency living in the northern hemisphere?

  14. Carina April 26, 2019 at 9:41 am

    Hi Keya,

    I’ve chosen a passive solar house design with clerestory windows facing south to be built southern Ontario, Canada. Could you tell me the best roof angles and overhang needed to achieve optimal passive solar?

    Warm Regards!


  15. Keya Lea April 11, 2020 at 3:59 pm

    That all depends on the lat/long of where you live, combined with local weather conditions, as angles and roof overhangs are impacted by snow and rain, cloudy days and other factors that aren’t often considered. For example, if it rains a lot, where you are, the angle of the roof will impact overall drainage. Drainage (water) could impact the overall building’s temperature and ability to maintain a constant temperature.

    Optimal passive solar is more impacted by the amount of solar gain (windows) and the thermal mass that can absorb the heat from the solar gain. The best to find out information about angles and overhang would be to talk to local passive solar builders and other home owners in your area.

  16. Keya Lea April 11, 2020 at 4:01 pm

    If someone lives in a desert, or other extremely hot area where solar gain from the south is not desired, it could be possible to build a more efficient house that stays cool by building windows to face the north, in the northern hemisphere.

  17. Keya Lea April 11, 2020 at 4:17 pm

    Yes, that makes sense. In regard to maximizing the solar gain and the solar heat that could be used in the house to moderate the temperature, it would depend on the thermal mass that can absorb the solar heat that is allowed in the house by the windows. The sun that enters the house and strikes various surfaces (floor and walls) will impact how much solar heat/gain the house has through the winter. The surfaces that absorb, then later remit heat, are those that have thermal mass, like brick, stone, adobe, tile, and other dense materials. Depending on the material of the wall, if it has thermal mass, more solar gain can potentially be achieved, regardless of the angle of the southern facing windows.

    Depending on where you’re located in Wisconsin, the overhang of the roof will also impact how much winter solar gain can be achieved, I think, more so than the angle of the windows. Hope that makes sense, and hope your build is going well. 🙂

  18. vipin July 5, 2020 at 12:21 am

    Interesting article, simple to understand.

  19. Feng Shui October 14, 2020 at 6:18 pm

    Any advice, say, in a hot tropical country, a rectangle house with long side facing east-west, which means the challenge would be the afternoon sun & heat. How to design in such a way to overcome too much sun light & heat problem?


  20. David November 5, 2020 at 7:27 am

    Hi. Please explain further: “ Orientation
    It is ideal to have the windows (solar glazing) within 5 degrees of true south. However, windows that are within 15 degrees of true south are said to function almost as well.”
    Is the 5 degrees more to the east or west. Thanks.

  21. Keya Lea December 4, 2020 at 8:11 pm

    I believe if the thermal mass and overhang are close to ideal, then the variance of the degrees to the east or west has been found to not be as significant, as solar gain is achieved throughout most of the day. I think the efficacy is similar for the angle to the east or west.

  22. Keya Lea December 4, 2020 at 8:18 pm

    In the case of a building in a hot, tropical country, you’d want to keep the sun away from the thermal mass in order to keep it cool. If most of the solar gain is in the south, you’d want to keep the house and thermal mass (brick, adobe) shaded from the sun. For a house like this consider putting windows where there will not be direct sun, or build an appropriate solar overhang to help keep the house cooler.

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.