daylight and passive solar

Daylight and Passive Solar Design for Remodeling and Adding onto Existing Buildings


When we take on an existing building, we always look for ways to improve its relationship to the sun. Some of the most important aspects of sustainable buildings aren’t new technology, but the basic concepts of layout in response to the surrounding environment.  Today we discuss how working with daylight can improve energy efficiency, reduce power demands, and improve your whole day.

Why design for daylight?

The sketch in the header shows the backyard of our latest project to begin construction: the Carmen Avenue House; summer direct light is blocked but the winter sunlight (and heat) are welcome.

Not only did we re-arrange the layout to maximize comfort and flow, but we improved its daylight and passive solar potential as well.  The overlapping orange lines show that for the new Family room (at yard level), winter sun will shine right in, lighting the space and warming up the new concrete floor slab (to warm the space all day and part of the night).  The kitchen will always have plenty of indirect light but won’t get any beating direct rays.

  • Save energy – more natural light means less artificial light, less power requirements – especially at peak load times (when businesses are open and drawing power and when the bulk of electric cooling is needed)
  • Bask in the Warmth and Keep your Cool – planning around seasonal sun patterns (and taking a few key passive solar steps) means that you can stay shady and cool in summer but boost your heat intake in winter without lifting a finger or burning any fossil fuels.
  • Gain Energy – this 2014 Northwestern study is only one of many which find that natural light is good for people.  In this case they showed that office workers in daylit workspaces slept better and had better activity and quality of life than their artificial light colleagues.  Let the light shine in!
  • Enjoy the Sunshine – while we love a well designed light fixture there is no substitute for sunlight in providing a variable, …. light source. Shine on, sunshine.

The benefits of designing with the sunshine are clear, at Carmen Avenue house, and everywhere.

Daylighting and Ancient Buildings

One way to think of this is as an ancient “technology” for sustainable buildings.  Paying attention to the sun, and making use of its heat and the cool of shade are concepts used my many ancient cultures.

For example, the Pueblo structure at Mesa Verde took advantage of the thermal stability of building into a cliff-face (cool in summer) and constructed a whole community under the protective shade and rain shelter of an overhanging cliff.  In summer, the higher sun was blocked out by the rock overhead.  In winter, the lower solar angle lit and warmed the whole structure, baking in heat that could linger into the night.

Daylighting and Older Buildings Here in Chicago

Older homes and commercial buildings (like the type that Moss often works with) are often pretty strong on natural light.  Even long after the development of artificial light sources, natural light (and ventilation) was considered a good building practice.  Higher ceilings, larger windows, and narrower floor plates all ensured that natural light could reach most parts of every building.


When we work with existing buildings – a common occurrence for moss projects – we study the ways that the building already maximized daylight and passive solar potential, then look for possible improvement.  Are there unnecessary interior walls separating a kitchen from the best like (as at Melrose House shown above)?  Perhaps we can remove them.

In other cases we re-arrange the floor plan to move shared spaces into more ideal locations for sunlight as at the Carmen Avenue house.  The back-yard oriented solar aspect cried out for us to place a greater importance on the connection with south wall of the building.

carmen avenue gif_sustainable copy 2

General Principles and Best Practices

Good daylight design is about more than cutting holes for extra windows.  We consider orientation of the building, wall-to-window ratio, window placement/shape, and exterior shading devices.  We calculate how letting in light will affect the heating and cooling load and the insulation of the thermal envelope.

For buildings in hot climate it might be most important to focus on indirect light sources (north and east) while keeping any heat gain out of the building.  Choosing the necessary windows for effective Solar Heat Gain Coefficient (SHGC) and emissivity (low-e) can also help keep unwanted heat out of building.

In a cool climate (like ours) however, direct light can be harnessed as a home heat source, through passive solar design.  Buildings with a south facing aspect can let winter sunshine shine in onto a thermal mass – a surface that will slowly absorb the heat of the sun and then release it slowly after the sunlight has gone – like a concrete floor or stone wall.  A well insulated building (capable of holding onto that heat) with good ventilation (to let out extra heat if necessary) can offset some or even all of its heating needs on sunny days.

Passive solar is too unpredictable to be a sole heat source – it can’t replace your furnace entirely – but it can seriously offset artificial heat sources under the right conditions.

Daylight from Four Directions

  • North: best for even, indirect light; no harsh glare or shadows; preferred by artists;
  • East: morning light, sunrises (and moon rises); this can warm a house after a cool night but poses no threat of overheating in the summer;
  • South: can run the risk of overheating and glare; however, it is relatively easy to control with well calculated shading devices like roof overhangs and awnings;
  • West: low slanting sunset light, especially in the late summer, can add unpleasant glare and a lot of heat. This is the most important light to control with shading from trees or adjacent structures.

Shading and other Natural Cooling Methods

Speaking of shading, you can also plant trees – or take advantage of existing trees – for shade as well as working with existing buildings to block out that harshest, hottest, western light.  Deciduous trees to the south block heat in summer and let in winter light.  When all else fails, turn to window treatments.  Judicious use of shades can block, or diffuse, natural light making it work for you not against you.

Taking advantage of stack ventilation will help your building cool itself; by making a pathway for hot air to escape from the top, cool air will be drawn in from lower windows and create a breeze.  

For more on moss’s views on natural light, check out our post on Windows: the Light of Interiors and the Soul of Buildings.  We’ll be happy to take you on a tour of some of our favorite projects with great daylight solutions.