Passive Solar Design

Early on, when I was learning about green and sustainable living, I realized it’s possible to design an energy-efficient home without a lot of added cost. In my opinion, the right design is the most critical piece of the entire green building philosophy. It’s the part that honestly doesn’t cost you anything extra.It’s the part I’d like to talk about a little today.

Okay, so what’s the secret?

Really, there isn’t a secret. Our ancestors knew about passive solar design: They practiced smart design in the way they laid out and positioned their homes. They paid attention to the path of the sun and its position in the sky. They knew the direction of the wind. They simply paid attention to what was going on with the piece of land they wanted to build on. They knew trees would provide shade. They knew deep porches around the house also provided shade from the sun and protection from the elements. They knew if they turned the house just right they could catch some of that breeze to help cool the house. Oh, sure, with building science today we are way beyond that simple approach for building our homes, but those basic principles are still the key to effective green design.

Good green design begins in the proper orientation of your home on your lot, plus a design that works with the uniqueness of your lot and how you prefer to live.So where do we start?

First, we start with proper orientation and respecting the climatic conditions of the location. Where’s the sun? Where’s the sun in the summer? Where’s the sun in the winter? While the sun provides light and heat, the sun can also dramatically affect the comfort of your home. In central Texas, we want to put most of the windows on the north and south sides of the house, and minimize and shade windows on the east and west. We want to position windows for cross-ventilation.

Second, what do you want your home to do? The way you live is an important part of the process and is often overlooked. In my previous blog posts, I’ve mentioned the importance of listing your wants, your needs, the way you live, the way you want to live, what you want to accomplish with your new home or your remodel project in the aspect of sustainable or energy efficient systems and practices. These are all important pieces of the puzzle.

When you’re thinking about your new home and looking for that perfect piece of property, put some thought into windows. This is that part about how do you want to live in your house. Are you a natural light junkie and want as much daylight as possible through the whole house? Or are you more of the cave dweller when it comes to daylight? Maybe it’s only specific rooms where you want lots of daylight.  Maybe you just can’t stand the morning sun in your bedroom but are equally frustrated with the heat of late day in your bedroom.

Ah, you want lots of natural light but don’t want to deal with all that heat? What can we do?


A basic step is to minimize the amount of direct sunlight coming in a window. We start with longer roof overhangs, or eaves. Based on the solar angles in the Austin area, the roof overhang needs to be at least 24 inches. This can get quite technical, and I’m not going to get into the data and details; you can go read about it if you like. So I’m simplifying a little, but this 24-inch overhang combined with appropriately sized windows and the height of the window off the ground will give you some good protection from direct sunlight. Beyond that, we can add porches, pergolas, shed roofs, awnings, and the like, and extend small portions of the roof overhang over larger or lower windows. And trees! We take advantage of trees by positioning the house so trees provide shade.

Want to play a game? As you drive around, notice which homes are properly oriented and which are not. Which homes have vast expanses of exposed windows on the west? Which homes have protective roof overhangs? Which do not? Which homes have porches and other structures to provide protection? Which do not? Which homes are likely to be comfortable, and which are not?

Let’s switch gears a moment.

Are you considering adding solar photovoltaic panels? As long as they get sun, we get power, right?  Well, not exactly! For best effect, solar panels need to be located in the “sweet spot” on your rooftop. This is something that is directly related to where you are located on the globe and the angle the sun hits you as a result. For us here in Austin, our sweet spot is south-facing. Which means we need a large enough roof area facing south to hold all the solar panels we need. Tie with that the angle of the sun for this area and it gives you the best angle for your roof pitch. (Roof pitch is a numerical measure of the steepness of a roof.) To get the most out of the sun here in Austin, we need about a perfect 30-degree angle.

Another thing that affects the placement and efficiency of solar panels is shade.  Here’s where all those trees on your lot or maybe even the neighbors trees come into play. Unfortunately, you have to be aware of things that will cause shade on your solar panels because once they’re in shade you’re not getting any “solar power.” It’s exciting to have lots of wonderful big trees you can plunk your new house in the middle of. But the down side? If you’re counting on those trees shading your entire house, then using solar panels becomes a real challenge.

A well positioned house and one that’s designed for how you live with and use the sun can reduce your heating, cooling, lighting and maintenance costs. And that, after all, is the very core of green design. It’s as simple as making the sun and wind work for you on your specific piece of property instead of working against you.

  • It’s doing things like placing your garage to face west so it serves as a block for the rest of the house against heat gain.
  • It’s things like placing most windows to face south or north. South gives you brighter light all day but also increases chance for heat gain. North gives you constant low level light all day with minimal to no heat gain.
  • It’s things like placing windows throughout the house to catch southerly breezes.
  • It’s things like locating your house near trees that give shade and block direct sun.
  • It’s things like locating the kitchen to face more east to get great light in the morning but not lots of heat in the evening when you’re cooking dinner.
  • It’s things like covered porches deep enough so you can enjoy that outside kitchen and not bake in the afternoon sun.

These and many other ideas make good design sense.  With a little pre-thought about how you live with the sun, you’re miles ahead when you meet with your architect/building designer.

Note:  For those of you reading this who don’t live in Texas, please remember something for me: This blog post deals with sun angles and wind directions specific to central Texas. What works for us won’t work for folks in Maine.  The green design professionals where you live should be able to help you with all of this.

There are many wonderful resources out there about this topic, orientation or frequently referred to as passive solar design. There are lots of good books. Two are Green Building for Dummies by Eric Corey Freed, and Your Green Home by Alex Wilson. You can find lots of information online. Give a try – the web site has tons of good information. Just have some fun and do some web surfing!