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Building Science

Building Science is the design and construction of the walls, roof, floor, windows, and their connections as a single system that controls air, heat, moisture, and bulk water. In a hot-humid Central Texas home it matters because the pressure is mostly inward: for much of the year outdoor air is warmer and far wetter than indoor air, so leaks and vapor-open assemblies carry moisture toward the cool inside face rather than away from it. An envelope detailed for a cold climate, or not detailed at all, can put condensing conditions inside the wall while the house still feels fine to stand in.

What the envelope has to do here

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Four control layers — water, air, vapor, and thermal — need a continuous, drawn path around the whole enclosure, including at transitions, penetrations, and the roof-to-wall junction, where most failures start.
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In a predominantly cooling climate, vapor drive is generally inward during humid months, so the vapor-control strategy that works in the north can trap moisture here.

Air control

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Air leakage moves more moisture than diffusion does in most assemblies, which is why we treat the air barrier as the primary moisture-control measure and verify it with a blower-door test rather than assuming it.

Drying capacity

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Assemblies should be able to dry in at least one direction. We prefer designs that keep condensing surfaces warm and leave a drying path, rather than designs that depend on nothing ever getting wet.

How we verify it

Envelope claims are only worth what the test data behind them says.

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Airtightness is measured, not estimated, and the result is recorded in The Sage Co. Record with the date and the test conditions.
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Pre-cover review is a scheduled milestone: assemblies are photographed and inspected before insulation and drywall conceal them.

What we do not claim

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A tight, well-detailed envelope does not by itself make indoor air good. Tightness raises the importance of designed ventilation; it does not replace it.

Sources

Primary references for this page. Where a statement is graded Emerging, the source supports the question being open, not a conclusion.

1. Building Science Corporation — building science digests and reports — Building Science Corporation
2. Building America program resources — U.S. Department of Energy
3. ASHRAE standards and guidelines — ASHRAE