tyvek on new house?

I'm building a new home . The builder offers house wrap for 750$ (1800 sq. foot ranch) But claims it is not nescessary. He installs r-13 unfaced fiberglass in all walls and covers inside exterior walls with heavy vinyl. All outlets have foam insulation behind them. He seems to pay attention to details and builds a tight house. Is the wrap nescessary or not.

 

I would say it depends on how fast your siding is going up, if right away I guess it would be OK without it, if it's going to be even a couple rain storms in between, then I would wrap it, 750 worth of wrap could save 2 or 3 thousand worth of plywood. Personally I always wrap a house, just another line of defense against elements, closes off any small gaps in plywood etc., less air infiltration.

 

Tyvec and similar products are sometimes called air barriers. In reality Tyvec and builders felt are drainage planes and all siding materials are counter flashing. In other words, siding materials are the first defense against water penetration and drainage planes are the last defense.

Builders felt is installed by applying a row at the bottom of the sides of the house and then applying another row above it making sure the top row overlaps the lower row. The seams between the rows are not sealed deliberately to allow moisture generated inside the house to escape the structure.

Tyvec and similar products are applied in large sheets and the seams are deliberately taped. This is because this type of product is designed to repel water and at the same time allow mosture generated inside to escape easily through it. This product was developed because of the problem with wind driven rain and hot humid air during the summer.

Though rare, it was found that rain during a severe storm with high winds managed to push water past the siding and up the builders felt. Which cause damage to the wood underneath the builders felt. But in most cases the builders felt was either ripped when installed or when the siding was being installed that caused the wood damage.

The real advantage to Tyvec and similar products is that it is an air infiltration barrier. This is especially good if the house uses air conditioning a lot. This is because warm air condenses on cooler surfaces. It has been found that the builders felt allow hot humid air to enter the wall cavity when there is sufficient wind. The Air/Vapor barrier on the interior wall prohibits this warm moist air from entering the home. But the air conditioning inside the home, cools the wall, making the inside cavity of the wall a cool surface for the warm moist air to condense.

I don't know any new house built today that doesn't come with central air conditioning and even if it didn't, you would probably use window units. Of course it does depend upon the area you live in and your own personal habits and preferences, but for $750. as a preventive measure, in my opinion, is well worth it.