Architectural Flashing Supply
Start a Quote
Building enclosure control layers · Lesson 2 of 4

Building enclosure control layers: materials, standards and design constraints

The 2021 IECC air-leakage limits by tier with units and test pressure, how a failed whole-building test is handled, BSC's vapor retarder classes and climate guidance, thermal bridging categories, and how a specification writes continuity and QA.

You will be able to: Read the air-leakage criteria for a material, an assembly and a whole building with their units and test pressure, place the vapor retarder classes, and say what thermal bridging adds, each with its edition and source.

15 min · 12 slides · 13 questions

All lessons in this module
Slide 1 of 12

Three tiers of proof

Air-leakage proof comes in three tiers: a material, an assembly of materials, and the whole building.

The 2021 IECC prints the limits on these slides in cfm/ft2 and in L/(s·m2), at a pressure difference of 75 Pa (0.3 in. w.g.).

Each tier is ten times looser than the one before it.

Air-leakage criteria by tier, 2021 IECCDot plot on a logarithmic axis of air leakage in cfm per square foot at 75 Pa. Material: 0.004, which is 0.02 L/(s per square meter). Assembly: 0.04, which is 0.2. Whole building: 0.40, which is 2.0. A fourth row shows the diagnostic range from over 0.40 up to 0.60 cfm per square foot, which is 2.0 to 3.0, where the 2021 code asks for a smoke tracer or infrared evaluation and a report. Each tier is ten times the one before.Air-leakage limits climb tenfold per tier0.0010.010.11.0MaterialASTM E21780.004 cfm/ft²(0.02 L/(s·m²))AssemblyASTM E23570.04 cfm/ft²(0.2 L/(s·m²))BuildingASTM E7790.40 cfm/ft²(2.0 L/(s·m²))Buildingdiagnostic range0.40 to 0.60(2.0 to 3.0 L/(s·m²))Air leakage, cfm/ft² at 75 Pa(log scale)Over 0.40, up to 0.60: the code asks for asmoke-tracer or infrared check and a report.Source: 2021 IECC C402.5 (ICC excerpt).

Dot plot on a logarithmic axis, cfm per square foot at 75 Pa: material 0.004, assembly 0.04, whole building 0.40, and a diagnostic range from 0.40 to 0.60. Each tier is ten times the one before. Metric equivalents are 0.02, 0.2, 2.0 and 2.0 to 3.0 L/(s per square meter).

Values from the 2021 IECC C402.5 as ICC prints them, all at 75 Pa. The axis is logarithmic, so equal steps are tenfold. Check the edition your jurisdiction enforces.

Sources

Glossary

Perm
The unit of water vapor permeance BSC uses to class vapor retarders: Class I is 0.1 perm or less, Class II is 1.0 perm or less and greater than 0.1, and Class III is 10 perm or less and greater than 1.0.
Air leakage rate (cfm/ft2 at 75 Pa)
How much air passes through each square foot of a material, assembly or building envelope when the pressure difference is 75 Pa (0.3 in. w.g.), the pressure at which the 2021 IECC prints its limits.
Linear transmittance
The BC Hydro bridging guide's term for the additional heat flow caused by details that are linear, such as a parapet or a slab edge.
Guide specification
A federal template such as UFGS 07 27 10 that a project specification can adapt. Its bracketed values are template values, not code limits.