Tyvek® HomeWrap® - House Wrap
"As important to a home as insulation."

Products Typical Use: as an underlayment used prior to new siding installation or a siding renovation.

Manufacturer Web site: Tyvek HomeWrap's Web Site

Tyvek Explained (from Tyvek's web site):

Tyvek® HomeWrap®
as important to a home as insulation

With more than 30 years of residential performance on millions of homes, Tyvek® HomeWrap® is the world's leading house wrap. Wrapping a home in a protective envelope is a good building practice that helps combat a home's worst enemies: water, moisture and air infiltration. Tyvek® behind a home's siding is an excellent secondary defense against the weather.

What is HomeWrap®?
Tyvek® HomeWrap® is a weatherization membrane that provides a protective layer under a home's siding and over the sheathing. It is literally wrapped around a home over the wood or foam sheathing, cut out around windows and doors and taped at the seams.

The unique, nonwoven-fiber structure of Tyvek® HomeWrap® resists air infiltration and water intrusion, yet is engineered to readily allow moisture vapor to diffuse through the sheet, helping prevent mold and mildew buildup and wood rot. The fibrous structure is engineered with microscopic pores that readily allow moisture vapor to evaporate but are so small that bulk water and air cannot penetrate. Siding, whether it's vinyl, wood, stucco, brick, or composite, does not completely prevent air and water penetration. Tyvek® is designed as a secondary defense to help manage a home's wall systems.

How Tyvek® Improves Wall Performance
Tyvek® Protects Insulation R-Value -- R-Value ratings for insulation are only maintained as long as the air within the insulation stays still and dry. The Department of Energy estimates that nearly 40% of a home's energy loss is the result of air infiltration caused by wind driven pressures from the outside. The opposing forces of pressure between inside and outside walls cause heat and air conditioning to be virtually sucked from a home-- through walls, ceilings, sill plates, sheathing joints, top plates, electrical outlets and every inch of the estimated half-mile of cracks in newly constructed homes. As air infiltrates, it causes changes in temperature that require heaters or air conditioners to work harder. Constant temperature fluctuations also reduce comfort levels. Occupants feel too cold or too warm. Reducing air infiltration, increases a home's comfort factor.

Insulation can help increase the R-value, but it is only marginally effective in reducing air infiltration. When air infiltrates, the R-value itself can be reduced up to 60%. Adding thicker insulation won't solve the problem. Stopping air from getting in will.

Properly applied, Tyvek® HomeWrap® helps reduce air infiltration, preserving R-values, conserving energy, reducing heating costs and creating a more comfortable interior.

Tyvek® Helps Manage Moisture in Walls
The tighter a home, the more comfortable and efficient. Unfortunately, the tighter a home, the more susceptible to moisture problems that can cause mold, mildew and rot. So all systems need to be in balance--designed to manage water and moisture effectively.

There are two main ways water and moisture get into wall systems:

1. Bulk Water Intrusion from the exterior (rain and snow) can enter the wall and, if not allowed to dry in a reasonable amount of time, can raise the moisture content of the wood above 30% and cause rotting or mold and mildew. Tyvek® HomeWrap® has the highest water holdout of any secondary weather membrane.
2. Air Transported Moisture occurs when air leaks from the warm side of the wall to the cool side. Warm air will hold higher amounts of moisture than cold air. As warm air travels through a wall heading to the cold side, it will begin to cool and be forced to release moisture. This is called the dew point where condensation will occur. When there is a significant temperature drop across the wall, the dew point will occur somewhere within the wall. In the winter months the point of condensation is usually on the inside surface of the exterior sheathing. Moisture carried by air flow through the wall is deposited at the back side of the sheathing and accumulates. In hot and humid climates where air flow is traveling from the outside to the inside, warm moist air from the outside will be cooled on the way to the air conditioned inside, releasing moisture within the wall cavity. Tyvek® HomeWrap® is a breathable membrane with microscopic pores that allow the moisture vapor to dissipate, helping to dry out a wall system to avoid damage.

Tyvek® Breathes -- A critical feature for a home's walls
Moisture Vapor Transmission Rate or perm rate of a material determines the ability for water vapor to diffuse or evaporate through the wall. The higher the perm rate, the more "breathable" the material is and the easier it is for water vapor to pass through. Materials with Perms below 1 are considered vapor retarders since the rate of moisture vapor flow through a 1 Perm material is so low there is essentially no flow. Tyvek® has a Perm rate of at least 58 Perms which is very open to allow moisture vapor to flow through.

Tyvek® HomeWrap® has the best combination of air and water resistance, plus breathability of any secondary weather membrane available