Passive Solar Design for Texas Homes, New or Old

Passive solar design adapted to Texas heat: orientation, window placement, overhangs, thermal mass and cross breezes, plus retrofits for an existing home.

A passive solar home uses the building itself, meaning its orientation, windows, roof overhangs and materials, to collect, store and block the sun's heat without pumps, fans or panels. Most of what's written about passive solar comes from colder places, where the goal is soaking up winter sun. In Texas the job is mostly the reverse: keep the summer sun off the house while still letting some low winter sun in.

Long before air conditioning, Texans built this way. Dogtrot houses with an open breezeway, deep porches, tall ceilings, raised floors and thick stone walls in the Hill Country were all ways of living with the heat. The same ideas still apply to new construction, and plenty of them can be added to the house you already own.

How the sun moves over Texas

In summer the sun rises north of due east, climbs high overhead at midday and sets north of due west. In winter it rises in the southeast, stays low in the southern sky and sets in the southwest. That pattern drives every passive solar decision:

  • South-facing glass gets low winter sun and is easy to shade from the high summer sun with a simple overhang.
  • East and west glass gets hit by low morning and afternoon sun that an overhang can't block. The west side on a summer afternoon is the worst of it.
  • North glass gets steady, indirect light with very little heat.

Orientation and window placement

For a new home, the starting point is setting the long side of the house to face within about 30 degrees of true south, and closer is better. Living areas go on the south side. Garages, closets, laundry rooms and bathrooms make good buffers on the west. Keep west-facing glass to a minimum, since that's where the hardest summer heat gain comes from.

Window performance matters as much as placement. On east and west windows, a low solar heat gain coefficient (SHGC) keeps out more of the sun's heat, because lower numbers block more. On well-shaded south windows, a moderate SHGC can still let in some winter warmth. Our article on low-E glass coatings explains how coatings change these numbers.

Overhangs, porches and shade

A properly sized roof overhang on the south side shades the windows in summer and lets winter sun slip underneath. The right depth depends on window height and latitude, which runs from about 26 degrees north in the Rio Grande Valley to about 36 degrees in the Panhandle. Porches do the same job on a larger scale and give you shaded outdoor space as a bonus.

East and west walls need different shading because the sun comes in low. Deciduous shade trees, trellises with vines, exterior solar screens and awnings all work. Deciduous trees drop their leaves in winter and let the sun through just when you want it.

Thermal mass, used carefully

Thermal mass is any heavy material that absorbs heat slowly and gives it back slowly: concrete, brick, stone, tile or adobe. Most Texas homes sit on a concrete slab, which is already a lot of mass. Leaving parts of it exposed as stained concrete or tile, instead of covering it with carpet, lets it soak up extra heat during the day and release it at night.

In Texas, mass helps only if it stays shaded in summer and gets a chance to cool off at night. Mass that bakes in the afternoon sun keeps radiating heat into the house long after dark. That's why the shading comes first.

Cooling with air movement and the roof

Passive cooling leans on moving air. Windows on opposite sides of the house allow cross ventilation, and much of Texas gets steady southerly breezes in summer. High windows or a clerestory let hot air escape near the ceiling. Ceiling fans let you stay comfortable with the thermostat a few degrees higher.

The roof matters as much as the walls. A light-colored or reflective roof absorbs less heat, and a radiant barrier in the attic cuts how much of the roof's heat reaches the ceiling below. Our article on how a radiant barrier works covers that piece. Insulation and air sealing tie it all together. A well-oriented house with a leaky shell still won't hold its temperature.

Passive solar ideas for an existing home

You don't need to build new to use these principles. Practical retrofits include:

  • Exterior solar screens or awnings on west and east windows.
  • Replacing west-facing windows with low-SHGC glass.
  • Planting deciduous shade trees on the west and southwest sides, far enough from the foundation.
  • Adding or extending a porch or patio cover on a sunny side.
  • Pulling up carpet over the slab in a room that gets winter sun.
  • Adding a radiant barrier and topping up attic insulation to R-38 or more.

None of these is dramatic on its own. Together they can take a real bite out of afternoon heat gain.

Start with how the sun hits your house

If you're planning a new build or improving the house you're in, the first step is learning where your heat gain actually comes from. Texas Energy Pros offers a free home energy audit that looks at your windows, attic and roof and how the sun strikes your home through the day. Contact us to schedule a visit, or read more in our energy efficiency articles.