[CCMC 13253-R] CCMC Canadian code compliance evaluation

The assessment of the product’s durability is covered under CCMC 13119-R.

An air barrier material as part of an air barrier system

The CCMC has not evaluated the performance of the Tyvek^® CommercialWrap^® air barrier system as to its conformance with Article 9.25.3.2., Air Barrier System Properties, of Division B of the NBC 2015. However, the CCMC’s opinion is that an air barrier system using this material and installed in conformance with the details outlined below, as well as in conformance with DuPont™ Tyvek® Sheathing Membranes and DuPont Self-Adhered Flashing Products Installation Guidelines, should satisfy the requirements for continuity of the air barrier system in Articles 9.25.3.1., Required Barrier to Air Leakage, and 9.25.3.3., Continuity of the Air Barrier System, of Division B of the NBC 2015.

Discussion

Authorities having jurisdiction (AHJ) should be aware that this system differs from the typical air barrier approach, which uses a flexible membrane as the principal plane of airtightness. In the typical approach, the membrane (i.e., polyethylene sheet) is normally sandwiched between two other materials so that it is not required to resist, on its own, the full force of indoor/outdoor pressure differences induced by stack effect, mechanical systems and, most importantly, wind.

In a system in which the membrane is applied to the outer surface of the wall sheathing, as it is in the Tyvek^® CommercialWrap^® air barrier system, that membrane does not have continuous support against outward air pressure. The membrane must, therefore, have adequate strength to resist that pressure by spanning between points of support, such as its own fastening points or the points where strapping or cladding is fastened to the wall. The CCMC’s evaluation of the Tyvek^® CommercialWrap^® material does not include the evaluation of this strength or the strength of the continuity details. The AHJ must, therefore, determine whether the product’s air barrier system, described herein, meets the intent of Sentence 9.25.3.2.(1) of Division B of the NBC 2015, as being an effective barrier for the proposed construction in the proposed geographical/climate area. For example, the AHJ may deem the proposed air barrier system adequate for buildings in urban areas, sheltered sites or areas of low wind, based on their experience, but inadequate in areas of high wind and exposed sites in rural or coastal areas.

An air barrier system checklist for the AHJ to consider is below.

An air barrier system must:

1. have an acceptable low air leakage rate;
2. be continuous;
3. be durable;
4. have sufficient strength to resist the anticipated air pressure load; and
5. be buildable in the field.

Installation details

The product’s material is applied over exterior wood-based wall sheathing material complying with the NBC 2015. It does not contribute to an air barrier system until it is joined to the other components that make up the air barrier system of the building. DuPont™ Tyvek® Sheathing Membranes and DuPont Self-Adhered Flashing Products Installation Guidelines  outlines how the product’s material must be joined to the foundation wall, to windows and doors, to penetrations in the wall, and to the ceiling air barrier, thus forming the system.

A successful air barrier system installation is predicated on sequencing during construction. Coordination is required during erection of framing and after completion of the air barrier system to ensure that no other trade breaches the integrity of the installed air barrier system.

The proposed air barrier system is defined as possessing the following features:

1. Tyvek^® CommercialWrap^® material as the principal plane of airtightness;
2. accessories, including sealants and CCMC-evaluated sheathing tape (that has adhesion strength with Tyvek® CommercialWrap®  approved by DuPont) to maintain continuity at junctions with penetrations in the wall assembly (i.e., windows, doors, pipes, ducts, electrical outlets, etc.) and in accordance with continuity details in the DuPont™ Tyvek® Sheathing Membranes and DuPont Self-Adhered Flashing Products Installation Guidelines;
3. durability, meeting UV- and heat-aging requirements; and
4. exterior sheathing with specified fasteners and fastening schedule of the Tyvek^® CommercialWrap^® for structural support against anticipated pressure loads.

The air barrier system is to be built in the field by informed builders and reviewed by building officials. DuPont Canada has established a field monitoring program to ensure the proper installation of the air barrier system.

The figures below outline typical construction details on the installation of the Tyvek^® CommercialWrap^® – Air Barrier Material™ air barrier system in the field. See DuPont™ Tyvek® Sheathing Membranes and DuPont Self-Adhered Flashing Products Installation Guidelines for additional details.

All horizontal joints in the material must be overlapped by at least 100 mm and taped with CCMC-evaluated sheathing tape (that has adhesion strength with Tyvek® CommercialWrap® approved by Dupont). To maintain continuity of the plane of airtightness, the material must be sealed to the roof by using an appropriate transition membrane. The material should be secured underneath the transition membrane to ensure proper shingling.

Wood-based sheathing, glass-fibre-faced exterior gypsum board, or exterior gypsum board having a water vapour permeance of less than 60 ng/(Pa·s·m²) must be installed in accordance with Article 9.25.5.2., Position of Low Permeance Materials, of Division B of the NBC 2015.

For wood-based sheathing, a gap of not less than 2 mm must be left between sheets in accordance with Article 9.23.16.4., Joints in Panel-Type Sheathing, of Division B of the NBC 2015.

Since the foundation wall is part of the air barrier system, the product must be sealed to the foundation wall to maintain the continuity of the plane of airtightness. The sealant used must be compatible with the product. For example, silicone-based sealants must not be used. To maintain watertightness, Tyvek^® CommercialWrap^® – Air Barrier Material™ sheathing membrane must be installed over the flashing and taped to properly drain any rain penetration breaching the cladding.

When installed as the principal plane of airtightness, the product must be structurally attached with nails with plastic washers, screws with plastic washers, or appropriate brick tie anchors.

For wood-frame construction where the sheathing is plywood, insulated board, glass-fibre-faced exterior gypsum, or exterior gypsum board, use nails with plastic washers and brick tie anchors.

For steel-framed construction where the sheathing is glass-fibre-faced exterior gypsum or exterior gypsum, use screws with washers and brick tie fasteners.

All seams require a 100-mm minimum overlap, and both vertical and horizontal seams should be secured with a CCMC-evaluated sheathing tape.

The material must be cut and wrapped around framing at openings (see Figure 4). Cut ends should then be taped or caulked to the inside frame. To ensure continuity at this junction, a seal must be established with the window or door element (see Figure 5).

The plane of airtightness of the material must be made continuous with windows and doors that are part of the air barrier system for the building envelope. The material must be sealed to the window or door frames with either sealant/backer rod or filled with sealant foam. Sealants must be compatible with the material and adhere to the framing material.

All exterior electrical boxes or other penetrations through the material must be rendered airtight to maintain the plane of airtightness of the air barrier system. All electrical boxes must be wrapped and taped to the product’s membrane, or airtight electrical boxes can be used.

Where pipes and ducts may breach the Tyvek^® CommercialWrap^® – Air Barrier Material™ membrane, they must be sealed to the membrane. A sealant bead compatible with the product and the pipe or duct material or CCMC-evaluated sheathing tape is recommended.