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New HomeWrap helps keep wind, cold out, while keeping heat in

When you think of a warm house, the first thing you think about is the inside and the last thing would be the outside, especially when the winds and snow are blowing about.

But, it's what's on the outside that helps keep the inside warm.Such things as seams, joints and cracks can let in cold air, which makes keeping the interior warm a lot harder.

Which is why a number of quality builders are providing a secondary weather-resistant membrane, called Tyvek HomeWrap, for a more energy-efficient and comfortable home.

During tests on a typical wall hit by an average wind pressure of only 9 miles per hour, the installed R-value of the wall system went from R-14 to R-5 without HouseWrap. The systems with the housewrap maintained an R-13 installed R-value.

"Here in Utah we see Tyvek used behind all siding materials - stucco, masonry, vinyl and aluminum siding, and all wood sidings. It is important to remember that both air and water do penetrate all of these surfaces, and if water gets into the wall system, it can damage the wood and reduce the effectiveness of the insulation.

"If air gets into the wall cavity, and it does in conventional building practices, then the effective R-value can be reduced from an R-14 to an R-5. Fact is, R-5 is very common for homes built here in Utah. By adding Tyvek to that wall system we can achieve an R-13 wall system. Air infiltration accounts for as much as 40 percent of our energy bills," says Jim Jenson, Tyvek weatherization specialist.

What does a HouseWrap do for your home?

First, it acts as a barrier to significantly cut the flow of air and wind through the walls and inside the wall cavities.

Second, it must minimize penetration of bulk water, since the exterior wood, vinyl or masonry siding will not provide a 100-percent barrier.

Third, the membrane allows potentially damaging moisture vapor to escape from inside the wall cavity, so the membrane must be breathable.

DuPont Tyvek HomeWrap is a non-perforated, spunbonded sheeting that has been proven, in both field and lab tests, to have the best combination of air resistance, bulk water holdout and breathability.

Why use an air barrier?

The simple answer is to protect a home's installed R-value. Tests show that housewrap is just as important as insulation for keeping a home comfortable. Up to 40 percent of a home's energy loss can come from air infiltration through seams or cracks in exterior walls.

"We've found that in a typical 2,000-square-foot home a homeowner could probably save as much as $200 per year on their fuel bill with Tyvek. Typically, the payback period for a home being wrapped in Tyvek is 2 to 2.6 years," says Jenson.

Vinyl siding is flexible, so air naturally finds its way under the siding. Wood siding has many seams and can shrink, again leaving gaps for air to enter. Air moving inside walls can reduce the installed R-value of a wall system by as much as 63 percent.

Tyvek HomeWrap over the sheathing and under siding, stucco or brick preserves both the heating and cooling performance of a home's insulation.

Why use a breathable membrane?

Trapped moisture vapor can damage walls. Up to 70 gallons of moisture vapor can be generated daily inside a home from sources such as humidifiers, dryers, bathrooms, recirculating-type kitchen range hoods and more.

Even with proper ventilation, moisture vapor will still be present. If moisture vapor builds up inside a wall cavity, mold, mildew and rotting can occur.

Tyvek, a breathable membrane, lets moisture vapor pass through and dissipate through the cracks and crevices of the exterior siding.

An important feature in a breathable membrane is how it is made to breathe.

"The idea, here in Utah, can be compared to a sweater and a windbreaker in the winter. If it's cold outside but the air is still, then you can feel comfortable wearing a sweater. When the wind starts to blow, then a sweater won't do and you need a windbreaker to be comfortable. In a home, the sweater is the insulation and the windbreaker is the Tyvek," says Jenson.

A tight wall construction is crucial to building a comfortable, energy-efficient home. Proper ventilation, effective heating and cooling, properly installed insulation systems and a secondary weatherization protection like Tyvek HomeWrap, all work together to make a home work as it should.

"Everyone who builds a home pays somewhere along the line, it's just how much and for how long. Pay for Tyvek now and enjoy savings over the years to come. Or, pay for higher fuel bills over the longterm," Jenson notes.