Environmental Conditions & Stressors
Before we talk details of assemblies, we need to understand what the house is up against. This session builds a simple “site + climate stress profile” you can reuse all year.
Potential agenda
- Intro (2 min): “The environment writes the test.” What that means in practice.
- Desired outcome (6–8 min): A clear stress profile for the site + climate.
- Common failures (6–8 min): What happens when we guess wrong about the stressors (with examples).
- Core concepts (6–8 min): A quick mental model for choosing assemblies later
- Bulk water beats everything
- Wind drives rain (and pressure) into small defects
- Sun + temperature swings are “free accelerators”
- Details matter most at edges: roof-to-wall, grade, penetrations
- Takeaways (2–3 min): A repeatable checklist for “what this house will face.”
- Discussion (30–45 min): Compare local stress profiles and what they imply.
Desired outcome: a simple stress profile
By the end of this session, you should be able to describe the job site in a few sentences and identify the top 3–5 stressors that should drive design decisions.
Stressors to consider
- Rain + wind-driven rain: how often, from which direction, and how hard
- Snow/ice: drifting, ice dams risk, melt-refreeze cycles
- Ground water + surface drainage: slope, downspout discharge, splashback
- Cold + big daily swings: expansion/contraction and condensation risk at weak points
- Solar exposure: overheating, UV degradation, south/west orientation penalties
- Dry air: shrinkage/cracking, occupant comfort, material movement
- Wind: pressure loads, infiltration drivers, embers and debris in events
- Dust/smoke: filtration and intake placement implications (details later)
Potential discussion prompts
- Local reality check: What are the top 3 stressors in Northern Colorado for your projects?
- Site surprises: What site conditions have bitten you (drainage, exposure, wind, sun)?
Common failures (when stressors are underestimated)
These failures aren’t “mysteries.” They’re usually the predictable result of a missed stressor: water, wind, sun, temperature swing, or site drainage.
Common failure patterns Stressors → weak points → repeated exposure
- Leak paths at edges: roof transitions, wall-to-foundation, decks, penetrations
- Wind-driven rain: wetting behind cladding where flashings/WRB continuity is weak
- Ice and meltwater: damming and backup at eaves/valleys
- Sun-driven wear: UV and heat degrading exposed materials and sealants
Examples (for discussion)
Example 1 — “The windy wall”
Moderate rain + strong wind → repeated wetting through small defects → staining, rot, callbacks.
Example 2 — “Good roof, bad edge”
Roof field performs, but a transition (valley/skylight/chimney) leaks season after season.
Example 3 — “Drainage didn’t matter… until it did”
Downspouts and grading look fine on day one → long-term splashback and wet foundation zone.
Potential discussion prompts
- Top failure source: For you, what causes more pain: roofs, walls, or below-grade drainage?
- Design response: What’s one detail you changed because of local wind/sun/snow?
Core concepts
Bulk water is the main villain
Most expensive failures start with water getting in (or staying in). Everything else is secondary.
Wind turns “small defects” into “big wetting”
Pressure + rain finds openings you didn’t know you had—especially at transitions.
Sun and temperature swings accelerate aging
UV and thermal cycling punish exposed materials and amplify movement at joints and interfaces.
Site decisions are performance decisions
Drainage, exposure, and orientation can make an average assembly succeed—or a great one fail.
Takeaways
- A “top 3–5 stressors” summary for each project site.
- A habit of designing for edges and transitions, not just big flat areas.
- A reminder that wind + rain + sun + time is the real durability test.
- A short list of “never ignore” items: drainage, roof edges, penetrations, exposure, orientation.
Further reading & references
Keep these broad and practical: climate, exposure, and the “why” behind water-first thinking.
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BSD-003: A House Is a System
A reminder that site + climate + occupants + assemblies interact—no single “upgrade” fixes everything.
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BSD-014: The Four Control Layers
A fast framework for thinking about what must be controlled (we’ll apply it more deeply later).