The shadow before the light — la sombra antes que la luz — is not a poetic preference. It describes a design sequence: before placing a window, understand where the shadow line falls. Before specifying a finish, understand what light it will receive. Light and shadow control in house design is a series of decisions made in section, not in finish schedules or furniture plans.
Light Quality Is a Structural Decision
The quality of natural light in a room — whether it is raking and directional, soft and diffuse, or shifting and changing — is determined by window geometry, not by what the window faces or how large it is.
The variables are:
- Window head height: a high head height (ceiling height or above) sends light deep into the room and keeps the light source out of the occupant's direct field of view, reducing glare
- Window sill height: a low sill brings light close to floor level and creates shadow patterns on the floor; a high sill creates a light shelf effect above desk or work surface height
- Window depth in wall: a window flush to the exterior face produces no shadow reveal; a window deeply recessed in a thick wall creates a frame of shadow around the light, which gives the opening formal presence
- Glazing area relative to room area: a common ratio for living spaces is glazing area equal to 15 to 20 percent of floor area for adequate daylighting without glare
We establish these parameters in schematic design before the structural grid is fixed. Window size and position are informed by section analysis, not by elevation aesthetics.
The Roof Overhang Calculation
Overhang depth is calculated against the solar altitude angle at the site's latitude. This is not an estimate — it is geometry.
At Mexico City's latitude of approximately 19 degrees north, the sun's altitude at solar noon on the summer solstice is approximately 72 degrees above the horizon. The sun's altitude at noon on the winter solstice is approximately 48 degrees. A roof overhang over a south-facing window blocks sun above the cutoff angle it creates and admits sun below it.
For a window with its head at 2.5 meters above finished floor, and an overhang 0.9 meters deep at that same elevation, the overhang cuts off direct sun entering the window at approximately 60 degrees altitude — blocking summer midday sun while admitting winter sun. This calculation is drawn in section, verified with a sun angle tool, and adjusted before the structural drawings are produced.
A shallow overhang blocks nothing useful. An excessively deep overhang darkens the interior year-round. The correct depth is specific to the latitude, the window head height, and the orientation.
Material Reflectance and Shadow Behavior
The shadows that light creates inside a room depend not just on geometry but on material finish. A white-painted plaster wall returns light into the room. A dark concrete wall absorbs it. A polished stone floor reflects light upward onto the ceiling. A rough wood floor scatters it.
In MÉTODO, finish selection follows the light analysis. We ask: what will this surface do to the light that reaches it? For a north-facing room that receives only diffuse sky light, a highly reflective finish on ceilings and upper walls amplifies what limited light is available. For a south-facing room with strong direct winter sun, a mid-tone absorptive finish on the floor prevents the space from becoming uncomfortably bright.
The interplay between material reflectance and window geometry is a design decision, not a decoration decision. It determines whether a room feels luminous or flat, warm or cold, active or restful.
Shadow as Form Maker on the Exterior
Shadow quality on the exterior of a building is what gives facades depth and visual weight. A flat wall with flush windows has no shadow relief. The building reads as a diagram of a facade, not as a built object.
Recessed windows, projecting cornices, brise-soleil elements, and textured stone or concrete surfaces all create shadow. Shadow defines the three-dimensionality of a building in ways that no material finish can substitute for. A rough-faced volcanic stone wall has shadow at the scale of centimeters. A smooth stucco wall has no shadow except at the openings.
This is not a question of style. It is a question of how much information the facade gives the eye — how much there is to read at varying distances. At five meters, you read the overall composition. At one meter, you read the shadow cast by a projecting sill. Both scales matter.
Clerestory Light: Indirect, Deep, Consistent
For spaces that require good daylighting without direct sun — studios, kitchens, libraries, galleries — the clerestory window is more effective than a wall window of the same area. A clerestory is positioned near the ceiling, often on a north face or a roof monitor, and delivers diffuse sky light from above the occupant's field of view.
The advantages:
- No glare because the light source is above the horizontal line of sight
- Deep penetration into the room because light enters at a high angle relative to the floor
- Consistent quality through the day because the sky condition, not the sun position, governs the light level
The section determines whether a clerestory works. A single-story flat-roof building can accommodate a clerestory by raising one section of roof above another. A two-story building can use a roof monitor over the stair or central hall. These are section decisions made in schematic design.
Próximos pasos
Light quality in a finished house is the result of decisions made in the first month of the design process. If your project has moved into construction documentation without a deliberate light analysis — section drawings with sun angle overlays, window head height strategy, overhang depth calculations — those decisions have been made by default.
Conoce el método de MÉTODO to learn how light analysis is integrated into schematic design from the first site visit.