Air and Vapor Control Membranes

1. What are building-envelope control layers?

Control layers manage the flow of water, air, vapour and heat through the envelope. The water-control layer (the water-resistive barrier) sheds liquid water, the air-control layer limits air leakage, the vapour-control layer limits diffusion and the thermal-control layer is the insulation (S4). One membrane may serve more than one role, but each role must be designed and shown to work. Water control is covered on Water-resistive barriers; the guide Construction membranes for the building envelope covers the family, and the comparison Water-resistive barrier versus air barrier sets the roles side by side.

2. How is an air barrier different from a vapour retarder?

Source basis: S1, S2, S4; qualitative summary.

3. Where are these membranes used?

In walls, roofs and floors of residential, commercial and industrial buildings, including cold-storage and controlled-humidity spaces. Each assembly needs its own analysis of where moisture can come from and where it can dry. Roofing carriers are covered on PET spunbond roofing carriers.

4. When is a membrane suitable, and when not?

Reasonable candidates: products with air-permeance and vapour-permeance data under stated methods, tested assembly details and clear accessory systems for laps, penetrations and transitions.

Weak candidates: a vapour-impermeable layer placed where it traps moisture in the assembly, a membrane with no continuity detail at windows and penetrations, or one chosen from permeance alone without assembly analysis.

5. Which terms will I meet?

Air barrier, air permeance, air leakage rate, perm, permeance, vapour retarder, Class I/II/III, dry cup, wet cup, condensation, wetting and drying potential, climate zone, control layer, continuity, ABAA, ASTM E2178, ASTM E2357, ASTM E96. Glossary: density.

6. What air-permeance figures are cited?

The Air Barrier Association of America (ABAA) approval-process document for mechanically fastened commercial building wraps states a maximum air permeance of 0.004 cfm/ft² (0.02 L/(s·m²)) at a pressure difference of 1.57 psf (75 Pa), for specimens as received, tested to ASTM E2178-11, with no minimum listed (S5). For assemblies, a manufacturer technical note (S6) states that the maximum allowable rate required by most codes is 0.2 L/(s·m²) (0.04 cfm/ft²) at 75 Pa, tested to ASTM E2357, which is ten times the material limit, using 2.4 m × 2.4 m (8 ft × 8 ft) specimens and a loading protocol with sustained pressures of ±600 Pa, cyclic pressures of ±800 Pa and gust loads of ±1200 Pa; a second manufacturer page gives the same assembly figure (S1). The ABAA document did not state an assembly limit, so the assembly figure rests on manufacturer statements and the code text must be checked. ASTM E2178 tests a material; ASTM E2357 tests an assembly that includes joints, penetrations and transitions, which is why assembly limits are less strict per unit area than the limit on the material alone. Passing E2178 shows a material can serve as an air barrier, not how it and its accessories perform as a system (S6).

7. How are vapour retarders classified?

The International Code Council’s technical note TN06, citing the 2015 International Residential Code (R202, R702.7), defines Class I as 0.1 perm or less, Class II as above 0.1 and up to 1.0 perm and Class III as above 1.0 and up to 10 perms, with classes for typical materials determined by ASTM E96 dry-cup testing (S3); a control-layer handout repeats the classes (S4). The note gives sheet polyethylene and unperforated aluminium foil as Class I examples, kraft-faced fibreglass batts as Class II and latex or enamel paint as Class III, and warns that standard painted drywall is often over 10 perms and should not be counted as a Class III retarder unless the paint is rated at 10 perms or less; a given product’s class must come from its own test data (S3). Class requirements vary by climate zone and wall type in the code, and some assemblies allow or require none. The edition and local amendments must be checked.

8. How does climate zone change the choice?

For the 2015 IRC, TN06 reports that in cold climates (Marine 4 and zones 5 to 8) a Class I or II vapour retarder is required on the interior side of frame walls, but a Class III retarder is permitted where the listed vented cladding or continuous insulation is used; warm-humid, mixed-humid and other zones carry no IRC vapour-retarder requirement in that document, which does not list requirements for zones 1 to 4 except 4C (S3). Continuous insulation counted for this purpose must meet the minimum R-values in the table, and spray foam applied to the interior side of exterior sheathing qualifies if it is 1.5 perm or less at the stated R-value. Edition changes and local amendments alter these rules, and Canadian practice differs, so the code table in force and, where warranted, a hygrothermal analysis decide.

9. How does condensation control work?

Condensation occurs when moist air meets a surface below its dew point. Air leakage can carry far more moisture into an assembly than diffusion, which is why air-barrier continuity is often the more important first step (S4). The vapour retarder limits diffusion into the assembly, and the assembly must be able to dry in at least one direction. TN06 notes that where continuous exterior insulation meets the minimum R-value a Class I or II retarder is generally not required, and that Class I is not recommended there to avoid a double vapour barrier (S3). A second low-permeance layer on the other side can trap moisture; the “double Class II” situation (two low-permeance layers enclosing the wall) is a known caution in the handout and must be avoided unless analysis supports it (S4).

10. Does a retarder go on the interior or the exterior?

It depends. The location of the air barrier is flexible if it is continuous and supports wind loads; the vapour retarder’s location depends on climate and the temperature profile of the assembly (S4). Exterior insulation can keep the sheathing warm and change the answer. Use the code’s assembly options or an analysis, not a rule of thumb.

11. Why do continuity and penetrations matter?

An air barrier is only as good as its weakest joint. The handout stresses continuity at laps, corners, transitions between wall and roof, windows, doors and penetrations for pipes and wires, and notes taped housewrap or sealed membranes are used where the air-barrier role is assigned to them (S4). Assembly tests under ASTM E2357 include these details. The vapour retarder tolerates lapped seams better.

12. Which mechanical properties matter?

Tensile and tear strength for handling, puncture resistance, adhesion for self-adhered products, resistance to wind-load deflection and creep, and compatibility with tapes and sealants. For an air barrier supporting wind loads, deflection under pressure is a design question. Ask for data and methods; this page gives no numbers.

13. Which standards are named in the sources?

• ASTM E2178: air permeance of building materials (S1, S2).
• ASTM E2357: air leakage of air-barrier assemblies (S1, S2).
• ASTM E96: water-vapour transmission of materials; dry-cup and wet-cup procedures (S3).
• ICC-ES evaluation reports and acceptance criteria (referenced generally).

The standards themselves were not read; the editions and any withdrawn status must be checked.

14. How should different membrane types be compared?

Source basis: S1 to S4; qualitative and not a ranking.

15. How are these membranes made?

Polymer sheets are extruded, laminated or coated; nonwoven housewraps are spunbond or flash-spun; self-adhered membranes combine a carrier film with a bitumen or polymer adhesive and a release liner; fluid-applied membranes are mixed products cured on site. Details are proprietary; ask for a product description and test data. See also Silicone release liners for the liner of self-adhered products.

16. What installation points commonly decide performance?

• Surface preparation and priming for adhesion; temperature limits for self-adhered products.
• Lap widths, sealing and detailing at transitions and penetrations.
• Compatible tapes, sealants and flashings only.
• Protection from UV and damage before closing in.
• Inspection and testing, such as a blower-door test, after installation.

Source basis: S4 and general practice; follow the product’s installation guide.

17. What failures appear and how are they diagnosed?

Source basis: S4 for the double low-permeance caution; the remaining items are general practice.

18. How should a membrane be selected?

Define the assembly (wall or roof build-up), climate zone, interior conditions (for example high-humidity or cold-storage spaces), the control layers required by the code and design, the role assigned to each layer, and the penetrations and transitions. Then shortlist products with the data and accessories for those roles and check them in the assembly, not on a permeance number alone.

19. How should a membrane be qualified?

1. Obtain air-permeance data (material and, where relevant, assembly) with methods and conditions.
2. Obtain vapour-permeance data and the class by dry-cup and wet-cup methods as relevant.
3. Have the design professional review placement, climate and drying potential.
4. Define the tapes, sealants, flashings and details as a system.
5. Build a mock-up; test assembly air leakage where required.
6. Check the whole-building result after installation, for example with a blower-door test.

Source basis: S1 to S4; the sequence is general practice.

20. Which documents should be requested?

Technical data sheet with test methods, air-permeance and vapour-permeance reports, class statement, evaluation report or code listing where applicable, installation guide with transition and penetration details, accessory compatibility list, and warranty conditions.

21. What acceptance criteria are sensible?

Criteria belong to the project specification and code basis: material and assembly air-permeance limits, vapour-class requirements, mock-up pass and whole-building test limits where required. This page gives no project limits.

22. How should rolls be stored and handled?

Follow the manufacturer’s instructions: dry, covered, within temperature limits, rolls kept on end or as directed, and self-adhered products kept cool enough to avoid blocking. General practice statements only.

23. Which commercial formats are common?

Rolls in set widths and lengths, sheets, tapes and accessories, and fluid-applied products in pails or drums. Specify product, roll size, liner and accessory list.

24. What information is needed to request a quotation?

• Project location, code edition and climate zone.
• Assembly build-up and the role (air, vapour, water) assigned to the membrane.
• Interior conditions and any special humidity or temperature.
• Air-permeance and vapour-class data required.
• Accessories, details and quantities; roll sizes and destination.

Use the RFQ brief tool to assemble this in the browser.

25. What do purchasing teams usually ask?

Which data and test methods support the claims; whether tapes and details come as a tested system; what the warranty covers; minimum order and lead time; and who makes the membrane. Compare installed system cost, not only the roll price.

26. How should cost and performance be compared?

Compare installed cost per square metre including accessories and labour, the leakage risk of complex details and the cost of a failed blower-door test. A cheap membrane with poor accessories can cost more.

27. What regulatory and sustainability questions arise?

Energy codes increasingly require air-barrier continuity and testing; fire and flame-spread requirements may apply; substance declarations and recyclability depend on the product. This page makes no compliance declaration for any product.

28. What supplier qualification questions should be asked?

Who manufactures the membrane and accessories; what quality systems exist; how changes are notified; what training and site support are offered. See the supplier qualification checklist. PAXOMER does not confirm any supplier’s approvals or capacity on this page.

29. Which related pages should I read next?

• Guide: Construction membranes for the building envelope
• Comparison: Water-resistive barrier versus air barrier
• Related page: Water-resistive barriers
• Related page: PET spunbond roofing carriers
• Tool: Solution Finder

Engineering and purchasing FAQs

Each answer is general technical information, not a specification or a quotation.

Is an air barrier the same as a vapour barrier?

What air permeance is acceptable?

What are vapour retarder classes?

Should the vapour retarder go inside or outside?

Why does continuity matter so much for air barriers?

Can two vapour-retarding layers cause problems?

Is a housewrap an air barrier?

What information is needed for a quotation?

Does PAXOMER supply specific air or vapour control membranes?

Technical References

References below were opened on the access date shown. A source supports only the statement it is cited for. Standards are cited by number and title from public catalogue entries; their full text was not read unless stated.

1. S1. ASTM E2357: air leakage of air barrier assemblies. Henry Company (ASTM E2357 page). www.henry.com/resources/astm-e2357 (opens in a new tab) manufacturer literature · accessed 2026-10-27
   Manufacturer page; secondary summary of the standard (assembly limit).
2. S2. ASTM E2178: air permeance of building materials. ANSI Webstore (ASTM E2178-21 listing), 2021. webstore.ansi.org/standards/astm/astme217821 (opens in a new tab) standard catalogue · accessed 2026-10-27
   Catalogue listing of the material test method; the 0.02 figure was not confirmed from this listing.
3. S3. ICC Technical Note 06: vapour retarder classes. International Code Council (Technical Note TN06, vapor retarders). www.iccsafe.org/wp-content/uploads/proclamations/TN06-Vapor-Retarders_pdf.pdf (opens in a new tab) industry body · accessed 2026-10-27
   Technical note citing the 2015 IRC; current edition not checked.
4. S4. Control layers: vapor barriers and retarders (handout). Penn State PHRC (webinar handout). www.phrc.psu.edu/assets/docs/Webinars/PHRCWebinar_Control-Layers-Vapor-Barriers- (opens in a new tab) technical literature · accessed 2026-10-27
   Handout citing the 2015 IRC; undated.
5. S5. ABAA process for approval of air barrier materials: mechanically fastened commercial building wraps. Air Barrier Association of America (D-115-010 Rev 14 Part 3, mechanically fastened wraps), 2024. airbarrier.org/wp-content/uploads/2024/08/D-115-010-Rev-14-Part-3-Mech-fastened- (opens in a new tab) industry body · accessed 2026-10-27
   Primary approval-criteria document for one product category; upload path dated August 2024; revision currency not checked.
6. S6. Air barrier materials and assemblies testing. Sto Corp (technical hotline TH 0910, air barrier materials and assemblies testing), 2009. www.stocorp.com/wp-content/content/Systems_TechService/Air%20and%20Moisture%20Ba (opens in a new tab) manufacturer literature · accessed 2026-10-27
   Manufacturer technical note (the 0910 in the file name suggests September 2009; undated in the extract); describes E2178 and E2357 and one maker's results.