What is a Housewrap and Why is it Important?

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Housewrap is a synthetic material used to wrap the exterior of a building to protect the wall frames from external moisture penetration. A housewrap is technically referred to as a water-resistant barrier (WRB), a lightweight sheet installed behind the siding and sheathing of the house. 

Housewraps are expansive, quick to apply and improve the efficiency of the building envelope.

This article discusses the features and importance of housewraps for buildings.

Features of Housewraps

• The main objective of housewraps is to prevent the entry of moisture into the building wall cavity from the outside environment. 
• Housewraps, unlike most WRBs, housewraps are not impermeable. This allows moisture-laden air to enter the house, preventing it from being trapped within the wall cavity. Hence, all housewraps are WRBs, but all WRBs are not housewraps.
• The major types of housewraps available in the market are:
  • Synthetic or woven plastic housewraps: These wraps employ long threads running in length and width.
  • Nonwoven housewraps: These wraps employ shorter fibers in a random pattern.
• Housewraps are designed to resist air and water and allow the passage of water vapor. The woven or nonwoven fabric provides strengths to the housewrap. The fiber-spun technology imparts water and air resistance. The fiber pore size contributes to the vapor breathability properties of the housewrap.
• Housewraps should be installed over the sheathing and behind the siding. It can be used with wood, fiber, vinyl, brick, stucco, cement, or other sidings. Certain housewraps work best with specific types of siding materials, usually specified by the siding manufacturers.
• Figure-2 shows the location of the housewrap in a typical wall panel of a building.

1. Drywall panels
2. Wall framing and insulation
3. Exterior sheathing
4. Housewrap
5. Siding or cladding

• Housewraps are accompanied by the sliding or cladding process. Usually, housewraps, once installed, must be covered within 120 days because their exposure to UV rays can result in damage and leaks. Immediate covering of housewraps helps to increase their durability. 

Importance of Housewraps

Housewraps are a secondary defense against air and water penetration to keep water off from building framing and sheathing. It creates a high-performing home and helps to meet the International Building Code’s (IBC) minimum requirement for exterior walls.

1. Housewraps prevent air and water intrusions inside the home.
2. It prevents the accumulation of water within the wall assembly.
3. It creates a weather-resistant exterior wall envelope. 
4. It provides an energy-efficient, healthy and comfortable home.
5. Efficient installation of housewraps helps to reduce air leaks that, in turn, improve the thermal performance of the building.

Requirements of a Housewrap

Housewraps are available in different varieties in the market, and a suitable type is selected based on their performance. The performance criteria of housewraps are understood by studying certain key characteristics. This includes:

1. Water resistance of housewraps
2. Durability of housewraps
3. Vapor permeability of housewraps
4. Air resistance of housewraps
5. Drainage provided by the housewraps
6. Resistance of housewraps towards surfactants

The acceptance criteria as per ICC-ES (International Code Council Evaluation Service) are given in Table-1 below.

In addition to the characteristics of the housewrap, other factors that govern the performance of the housewrap are the type of cladding, the climatic conditions, the tightness of the wall assembly, and the exposure of the building. 

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