How to Build a Passive Solar Room Addition


Using the sun to heat your home is not a new idea. The Native Americans in the Southwest built their homes in south-facing cliffs to take advantage of the low winter sun. Their homes stayed cool in the summer because the sun was higher in the sky and didn't shine into their homes.

If your home has a south-facing exterior wall where you can build an addition, you can take advantage of free solar heat too.

Things You'll Need

  • Required building permit
  • Concrete floor
  • Windows and doors
  • Building materials

Add a Passive Sunroom

  • Site your passive solar room addition on the south side of your home. The best place is where there are existing doors and windows on the house, so you won't have to add fans to move the warm air into your rooms. If you don't have windows or doors to each room, you will have to add one fan for every separate room that the solar room covers. Check with your local building authority to obtain necessary permits or permissions.

  • Determine the size of the solar room based on your budget, home aesthetics and use for the room. A large solar room can be used as a greenhouse and expanded dining room. A small sunroom can hold a few plants and be a cozy spot for a chair to sit and enjoy the sunshine in winter.

  • Determine the thermal mass to capture the sun's energy. Since you need a floor, a concrete slab is the most obvious choice. In cold climates, the concrete should be insulated from the ground below it, but in warmer climates, the concrete should not be insulated because it acts as a heat sink in the hot summer months. For decorating purposes, the concrete floor can be covered with stone, ceramic, porcelain, or saltillo tile. Wood, vinyl or carpet will interfere with the solar gain and should be avoided. Masonry walls and dark colored barrels filled with water are additional sources of thermal mass to gather the heat in the solar room.

  • Choose double-glazed windows for the south facing wall. Used patio doors are an economical choice when available. For maximum solar gain, place the windows at a 30 degree angle. For ease in building, place the windows at 90 degrees.

  • Design the roof overhang to shade the windows during the summer months. The overhang is a large benefit of a solar room versus a greenhouse. The sun room with an insulated roof is a room that can be used yearround, while a greenhouse can become unbearably hot in the summer unless shade cloth is used.

  • Insulate the windows at night and on cloudy days to avoid losing the solar gain. Draperies that fit tight along the edges of the windows keep the cold at bay. Rigid insulation can be cut to fit inside the window frame and covered with fabric or wallpaper to match your decor. Shutters can be installed on the interior or exterior of the solar room to maintain the warmth and keep out the cold.

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  • Photo Credit living room shot image by Tracy Horning from
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