Rigid Underlay 'Over-Fixed' with Building Wrap or Proprietary Rigid Air Barrier System?

The main advantage of over-fixing with Tyvek is the building enclosure is sealed by a system of Tyvek weather tightness products that have been engineered by DuPont to work together.

This means the contractor, architect, territorial authority and/or building owner can worry less about 'incompatibility and/or durability issues.'

Although still in its infancy in New Zealand, plywood and/or oriented strand board (OSB) over-fixed with Tyvek has been installed on millions of buildings in North America for decades.

Rigid air barrier systems have the advantages of a solid substrate, durability, a bracing element, and some territorial authorities are allowing interior pre-finishing before cladding.

However, there are installation risks and technical properties that need to be thought through.

For drying of construction moisture or wall cavity leaks, high vapour permeability is necessary within the rigid air barrier system.

Questions to consider when specifying a Rigid Air Barrier System?

Do you know the vapour permeability of all products that make up the system?
How much water will the sheet absorb, and how long will it take to dry out? Will this affect structurally sensitive building elements and insulation?
Can you rely on the tapes and flashing to keep the wall weathertight for the life of the building?
Can the window cavities and penetrations be effectively sealed against water and air penetration?
Will the fixings create water entry points?
Is it airtight?

NZBC E2/AS 1 9.1.7.2 addresses rigid wall underlay requirements in New Zealand.

There are benefits and challenges to consider when specifying a Rigid Air Barrier System.

DuPont Tyvek HomeWrap Wall Underlay

Tyvek

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DuPont Tyvek HomeWrap is a breathable, fire retardant, synthetic wall underlay.

Cavity:
- All cladding types with both timber and steel framing
- Rigid Air Barriers, (over-sheathed)
Direct fixed:
- With absorbent claddings such as timber, polyymeric cladding, plywood, gypsum fibre cement, brick wood, and stucco plaster on timber framing, or over thermal break on steel framing
- Rigid Air Barriers, (over-sheathed)

All cladding types with both timber and steel framing
Rigid Air Barriers, (over-sheathed)

With absorbent claddings such as timber, polyymeric cladding, plywood, gypsum fibre cement, brick wood, and stucco plaster on timber framing, or over thermal break on steel framing
Rigid Air Barriers, (over-sheathed)

DuPont Tyvek HomeWrap Wall Underlay:

Can be installed in all Wind Zones up to and including Very High, or Extra High if over a rigid air barrier
A non-directional wall underlay meaning the wrap can be installed upside down or inside out and performance will not be compromised
Resistant to most surfactants meaning it is suitable for use behind Cedar Cladding (endorsed by the Western Red Cedar Association)
Can be used in all New Zealand climate zones
Can be used in all seismic and corrosion zones

As per CodeMark Certification, DuPont Tyvek HomeWrap, when installed in accordance with the recommended guidelines will meet or contribute to meet the following provisions of NZBC:

NZBC Clause B2: Durability. Meets the requirement of NZBC B2.3.1 a) 50 years and b) 15 years
NZBC Clause E2: External Moisture. Contributes to meet these requirements
NZBC Clause F2: Hazardous Building Materials. Meets this requirement and will not present a health hazard to people

DuPont Tyvek HomeWrap is an Acceptable Solution to NZBC E2/AS1

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