First of all, what is passive solar design? Incorporating a passive design, or passive solar design in your home means to take advantage of your local elements and climate such as the sun, wind, and terrain to achieve as near an energy neutral living space as possible.
The term passive solar design is often used due to the fact that the sun is by and large the greatest contributor in terms of energy that can be harnessed and used “passively”, or as is. Because of this, passive design generally focuses on things like window type, size and placement, insulation, structure location and orientation in relation to the sun and surrounding structures, awnings, and even the trees and landscape surrounding your home.
By incorporating these and other elements into your design approach, you can create an interior environment that relies very little on mechanical or “active” energy sources to maintain a comfortable temperature throughout the year.
*(When the term “south” is used in relation to the sun, this only applies to those in the northern hemisphere. Replace south with north for those in the southern hemisphere.)
The location of your home is perhaps the first thing to decide as far as the natural order goes. Thickly populated residential areas are tricky as prime real estate is generally taken or very expensive. South-east block corners are generally considered to be the most ideal as there will be a road acting as a buffer to your south and east — allowing you to take maximum advantage of the sun.
Developed countries generally have laws in place (maximum building height, minimum distance between structures, etc) to all but guarantee a certain minimum of direct sunlight, but it’s safe to say that when it comes to densely populated residential areas, there are the haves and the have-nots in terms of sunlight quality.
Structure Orientation and Roof Slope Direction
If you choose to live in a more isolated location, then the structure’s orientation becomes the next thing on the list. If you’re considering adding solar panels to your roof, then this is extremely critical to get right. A mono-pitched roof sloping downward toward true south (as opposed to magnetic south) is most ideal in terms of maximum roof surface area facing the optimal direction.
Hipped and gabled roofs, if you choose to go that direction, should have their largest faces sloping downward to the east and west, provided you have the means to place solar panels on both these faces. If you’re only planning on placing them on one face, then it should be on the largest face sloping downward to true south. See PV panels, Are They Worth it?-2 for more information on this.
Aside from the optimal orientation based on a possible solar panel array, there is the optimal orientation based on the sun’s direct effect to the home’s interior. In some cases, your roof slope and its direction won’t necessarily determine the orientation of the part of the structure beneath it.
Ultimately, the shape of your structure will largely determine what kind of roof would be suitable, as well as details of your floor plan, window placement etc. As in, it’s considerably easier and more plausible to shuffle around your floor plan to correspond to your roof if your structure was more or less square, as opposed to one that was a more irregular shape.
Window Size and Placement
This is kind of tricky to get right. The reason is because the right balance is slightly different from one person to the next. However, there are some rules of thumb you can follow to push you in the right direction:
– Too few windows will minimize the benefits of the sun (heat, light, etc), while too many will allow heat to escape overly quickly at night, as well as the opposite in the summer.
– The main cons to overkilling on windows is a possible lack of privacy, glares where you don’t want them, overheating in the summer (and even the winter in some cases), and bringing a less then ideal view into your home interior. I’ve heard it said that it’s better to have no or very few windows and make up for it by a home decor of your choice, than to open your curtains to a cinder block wall or parking lot.
– Large windows and glass sliding doors are generally best situated on the east and south sides of your home. The eastern sun lets light in first thing in the morning and isn’t as hot as the western sun. The bulk of the southern sun can generally be blocked by well-situated awnings, while still allowing you to place windows and doors to south-facing balconies and verandas.
– Tall, thin windows lined in a row, provide accent lighting to a dining or living room, while keeping a degree of privacy.
– Having a window in your toilet and shower room is ideal, as I think we can all agree that a fan on its own doesn’t always cut it. Of course, it should be translucent and possibly a louver window or one that doesn’t open all the way, with bars etc.
This is one of those hidden from sight, but extremely critical aspects of passive design. There are many types of insulation, ranging in both cost and effectiveness. But one ingredient that money sometimes can’t buy is high-quality workmanship. As far as insulation goes, you can have state-of-the-art product, but if installation is shoddy, its effectiveness can drop significantly.
The quoted effectiveness or R-value of an insulation will only hold if it is installed in the specified way. Generally, this infers a tightly packed network of insulation that has little or no gaps. From here you have to take into account wall studs and other thermal bridges, all windows, doors, vents, sleeves, and fans that add up to decrease a structure’s overall R-value.
Awnings are ideal to have in terms of passive design, but not always ideal in terms of the structure’s aesthetic design. However, this doesn’t change the fact that sufficiently protruding awnings are imperative to a good passive solar design. A well-designed awning will block the hot summer sun sitting high in the sky while allowing the low-sitting winter sun to warm the home’s interior.
Last but not least, large deciduous trees that cast shade on your home during the hot summer will shed their leaves in the fall, allowing the sun’s light and warmth to enter the home. Having to sweep up the leaves every year might make you want to chop the thing down, but think again.