Building Envelope, Moisture Protection, and Thermal Systems
Building Envelope, Moisture Protection, and Thermal Systems tests the building skin and the Florida Energy Code: water management, air and vapor control, insulation, fenestration, and the flashing details that fail first in service. FBC Chapters 13 and 14, plus manufacturer product approval, supply the rules.
Water management
- A wall needs a drainage plane: water-resistive barrier lapped shingle-style over flashing, behind the cladding, with weeps at the bottom and a weep screed at the base.
- Flashing sequence: sill pan under openings, head flashing above, and kick-out flashing where a roof edge dies into a wall. Get the order wrong and the lap reverses.
- Roof-to-wall intersections and penetrations are the highest-risk details.
Vapor and air
- Florida is warm and humid. Interior vapor retarders such as poly are generally inappropriate; vapor drive is often inward, so assemblies should dry to the inside.
- A continuous air barrier controls both energy and moisture. Air leakage carries far more water vapor than diffusion.
- Ductwork belongs inside the conditioned envelope; ducts in attics leak and sweat.
Thermal
- The Florida Energy Code sets prescriptive ceiling, wall, and fenestration values by climate zone, with a performance path and an energy compliance report.
- Fenestration is rated for U-factor and SHGC; impact products change both.
- Continuous insulation outside the frame reduces thermal bridging and is often the cheapest way to improve a wall's U-factor.
Worked example
A wall is R-13 cavity insulation plus R-5 continuous insulation, R-0.5 gypsum, R-0.5 sheathing, and R-0.2 air film: total R-19.2, U = 1/19.2 = 0.052. For 2,000 square feet, UA = 104. Adding another R-5 continuous layer gives R-24.2, U = 0.041, UA = 83 - a 21 Btu/h per degree F saving. Upgrading 400 square feet of window from U-0.40 to U-0.30 saves 40. Reasoning: compare UA, not R, when trading one component against another.
Traps that cost marks
- Installing an interior poly vapor barrier in a Florida wall.
- Back-lapping the water-resistive barrier over the flashing instead of shingle-lapping it.
- Relying on caulk at a roof-wall intersection instead of kick-out flashing.
- Ignoring thermal bridging through steel studs.
- Mixing prescriptive and performance compliance paths without the required documentation.