Vapor Retarders, Weatherproofing, and Finishes
What this domain tests
This domain tests moisture control and outdoor protection: where the vapor retarder goes, how it is made continuous, and how jackets and coatings keep water out and UV from degrading the system.
Core rules
- A vapor retarder belongs on the warm side of the insulation. For cold piping, that is the outside of the insulation. On below-ambient lines, every joint, seam, and penetration must be sealed.
- ASJ, all-service jacketing, is a common factory-applied facing with a low-permeance surface. Seal seams with the specified tape or mastic; do not rely on staples alone.
- Weatherproofing is different from a vapor retarder. Outdoors, use metal jacketing, UV-resistant mastic, or coatings, with sealant at laps, flashings, and penetrations. Detail the jacket so water drains.
- Metal jacketing must be installed with expansion room and secured with bands; sharp edges need protection.
- Finishes such as mastic or canvas are used for appearance, abrasion resistance, and sometimes vapor resistance; check the specification for permeance and temperature rating.
Worked example
An outdoor chilled-water line at 40°F in a humid climate needs closed-cell insulation, a continuous vapor retarder, and an aluminum jacket. Seal the vapor retarder at every joint with mastic and tape, then install the jacket with laps facing away from the weather and seal penetrations. The reasoning: the vapor retarder stops moist air from reaching the cold surface, and the jacket protects the vapor retarder from rain and UV.
Traps
Putting a vapor retarder inside a cold line; using a breathable finish where a vapor retarder is required; sealing only the jacket; and leaving the bottom of a horizontal jacket unsealed.