The section as relato — the section as narrative — is the design instrument that makes passive solar work at high altitude. Every passive solar decision is a sectional decision: the sun angle, the glazing position, the mass depth, the overhang, the envelope boundary. None of these can be correctly resolved in plan.
What the Passive Solar Section Must Show
A passive solar house section for a high-altitude site must document:
- The December 21 solar noon angle for the project's latitude, drawn as a ray entering through the south glazing
- Where that ray falls on the floor plane at winter solstice noon — this defines the solar gain zone and must coincide with exposed thermal mass
- The window head height and its relationship to the depth of the solar gain zone (gain extends approximately 1.5 times the window head height from the glass)
- The overhang or roof edge geometry relative to the glazing — does it shade the glazing in summer while the lower winter sun passes below?
- The insulated envelope boundary — a continuous line through wall, floor, and roof that should have no gaps or thermal bridges
- The thermal mass materials and their position relative to the solar gain zone
This section drawing is not a finished graphic — it is a working document that is updated through design development as decisions are made and as the glazing schedule and envelope assemblies are confirmed.
The Altitude Factor in Section Design
At high altitudes — above 7,000 feet in the Colorado mountains — passive solar design parameters shift in two important ways.
First, solar radiation intensity increases with elevation. The thinner atmosphere at altitude absorbs less radiation, so a surface at 9,000 feet receives measurably more BTUs per square foot of south glazing on a clear winter day than the same surface at sea level. This increases the passive solar gain potential.
Second, nighttime heat loss increases dramatically at altitude because cold temperatures are more extreme and sustained. A clear January night at 9,500 feet elevation in the Colorado mountains can drop to minus 15 degrees Fahrenheit. The same building that retains heat well in Denver loses heat quickly at that elevation unless the envelope insulation level and airtightness are proportionately higher.
The net effect is that at high altitude, both passive solar gains and nighttime heat losses are amplified. The design must respond to both. A section designed for Denver's foothills will under-insulate and under-mass a project at Summit County elevations.
Section Strategy: Direct Gain vs. Clerestory
Two common passive solar section strategies for high-altitude mountain homes:
Direct-gain section: large south glazing at the main floor level admits winter sun directly to the living spaces. The floor slab or stone tile below the windows absorbs and stores the gain. This is the simplest and most efficient passive solar strategy when the south facade has unobstructed solar access.
Clerestory section: where the south facade solar access is compromised — by topography, by lower portions of the roof, or by an entry canopy — a clerestory above the main roof plane admits high-angle winter sun into the north portion of the section. Clerestories are particularly effective for bringing light and gain into spaces that would otherwise be dark and cold. In MÉTODO, we draw the clerestory option as one choice in the matrix of options for sites with complex solar access situations.
Overhang Geometry from the Section
The seasonal overhang — designed to admit low winter sun while blocking high summer sun — is one of the passive solar section's most precisely calculable elements. The overhang depth is determined by:
- The altitude angle of the summer sun at summer solstice noon (approximately 73.5 degrees at 39 degrees north latitude)
- The altitude angle of the winter sun at winter solstice noon (approximately 26.6 degrees at the same latitude)
- The height from the glazing sill to the underside of the overhang
These three values determine the overhang depth through a geometric construction that can be drawn directly on the section. This is not an approximation — it is a calculation from solar geometry that produces a specific dimension. An overhang sized by rule of thumb will either overshade in winter or undershade in summer.
Envelope Continuity in the Section
The insulated envelope boundary must be drawn as a continuous line in the section before construction documents are begun. In MÉTODO, we trace this line through every element: from the under-slab insulation, up the foundation wall, across the exterior wall assembly, over the roof, and back — looking for every point where the line is broken by a structural element, a mechanical penetration, or a material transition.
Each break in this line is a thermal bridge — a path for heat to conduct from warm interior to cold exterior. At high altitude with extreme winter temperatures, thermal bridges produce not only energy loss but condensation and ice formation at the bridge location, leading to material damage. The section that shows a continuous, unbroken thermal envelope boundary is the section that avoids these failures.
Próximos pasos
If you are designing a passive solar house at high altitude and want to see what a correctly coordinated section looks like — with solar geometry, thermal mass position, overhang depth, and envelope boundary all resolved together — the design conversation starts at the section drawing board.
Conoce el método de MÉTODO to understand how we use the section as the primary instrument for passive solar and climate-responsive design.