5 Steps to Turn Any House into a Passive Solar House

In this post I teach you how to see your current house or even room through the eyes of a passive solar architect so that you may alter your behaviour and gain more comfort for less energy in your desired space.

How is this possible?

In short, by applying passive design principles to the way you use your house.

Whilst a custom designed passive solar residence is of course the best type of building to perform passively, there are many accidentally passively designed properties out there.

Even properties that, for a variety of reasons can be classified as the exact opposite of passively designed, can be made to perform towards higher thermal comfort and lower energy consumption simply by passive solar user behaviour.

Step 1: Orientation

Every building has sides and corners facing one cardinal point or another.

In a house, the rooms which are best positioned for passive solar design principles to work, are those running parallel to the equator with an arc of 0° to 20° East and West of that.

Rooms coloured in green (above) receive sunshine for the longest number of hours throughout the entire year, more than other rooms with any other orientation.

Passive solar design is all about shaping the features of a building’s walls and roof to deliver warm interiors in winter (allowing sunshine into interiors) and cool interiors in summer (shading interiors from sunshine). The higher the availability of sunshine, the higher the ability to shade or not shade it, the better chances to deliver comfort all year round.

Conversely, rooms with walls parallel to the poles receive the least amount of sunshine throughout the year, making them the worst candidates for passive solar design performance, but as we shall see they do have their uses.

Step 2: Room Use

Just because rooms in your house have a name (e.g. lounge, bedroom, or study) it should not restrict your use of them for most other purposes (e.g. meals, sunroom, or activity spaces). Laundries, kitchens, and bathrooms are the exception to this rule.

Do you have room which remains nice a cool on summer days but is absolutely horrible to live or work in during winter days because it is too cold? Perhaps you wish you could use this room as a lounge in summer and as a bedroom in winter?

In a passively designed house, room uses and seasonal temperature variations will have been thought of to avoid having to change uses, but  in a non-passive designed house, provided the floor area is big enough there is nothing stopping you from relocating furniture from one room to another and back again to accommodate for the seasons.

Here is a suggested room usage plan.

Step 3: Windows and Other Openings

Prevailing (regularly occurring) winds are natural air conditioners.

In passive solar design windows, doors, and openable roof-lights are one of the tools used to allow buildings to remain cool. Openings are positioned to catch and direct prevailing winds throughout a building. During hot weather, opening windows and doors will allow breezes to traverse the depth of the building and provide cooler conditions. During cold weather, keeping windows and doors closed will stop warmth from escaping.

If in a standard home opening a window allows air movement to flow into your room, it means you lucked out and this window has serendipitously been aligned with prevailing winds. If not, get to know the prevailing winds in and around your allotment both as a day-to-night cycle and throughout the seasons (you can get this information from your local bureau of meteorology website), and make a window opening plan. 

A good rule of thumb is any opening facing approximately perpendicular to any prevailing wind will allow air movement into your house. It is also helpful to remember that you can make winds flow through your house by opening various doors between rooms, thus allowing air movement to reach rooms where windows are not catching prevailing winds. Widows which face opposite to wind direction can be opened to let air movement back out of the house,  continuing rather than stopping wind speed through the depth of your home.

Step 4: Eaves and Other Sun-Shading Devices

Your roof eaves are not just there to look pretty and hold your gutters in place. They also shade your windows from sunshine.

In a passive solar designed home, the depth of the eaves (how far they stick out and away from your external walls) is precisely calculated to allow sunshine inside your house during winter when warmth is required and to keep it out during summer when warmth will make rooms uncomfortably hot.

The same logic as prevailing winds applies. If you are lucky, your eaves have been perfectly sized and you are getting rooms filled with natural light and warmth in winter, but shaded through the hotter summer months. If this is not the case here are a few remedies.

Install EXTERNAL retractable blinds to windows which allow too much summer sunshine into your rooms. It is extremely important that theses blinds be installed externally, stopping sun-rays (light+heat) BEFORE they get inside your room. Once inside, the heat part of sun-rays cannot escape back out and you will have a hot room; the result is the same with or without curtains (interior window coverings).

Build a verandah in front of windows that allow too much summer sunshine into your room. This renovation type remedy is best used on West, East, and equator facing walls. In a passive solar designed home, the depth of the verandah would be accurately calculated, however you can approximate this yourself by having some patience.

I suggest you have the basic structure built without putting on a permanent roof (install a pergola). Live with the pergola for a summer and install temporary shade cloth or retractable roof system progressively as you need it to shade interiors. Once winter comes, try move the tractable roof system or remove some of the shade cloth to find a happy medium between the shade you needed in summer and your new winter need for light and warmth.

Click here to find out why I suggest temporary shade cloth or retractable roof system initially.

At some stage you will notice that you are no longer adding to or removing the shade cloth, you have found your happy medium (or the depth to which a passive solar architect would have designed a roofed structure). At this point you may wish to permanently roof your pergola (install a verandah).

Step 5: Insulation, Insulation, Insulation

Your rooms get uncomfortably hot when too much heat is allowed to transfer (travel) from outside into your interiors, and your rooms get uncomfortably cold when too much heat is allowed to transfer from inside your rooms to outside.

Insulation in its many forms, is what slows heat transferring in the above manners. If you have followed Steps 1 to 4 you would have already worked very hard to make heat travel in the right direction to create comfortable interiors year round. Don’t let all your hard work go to waste, install insulation to your roof space, walls, and even your sub- floor space to extend the positive effects of your passive solar user behaviour.