Air & Water Barriers

Air and Water Barriers

I am amazed at how certain aspects of building technology seem to die or fade away. A great example of this is an inexpensive yet effective method of paving driveways. It is called tar and chip. This is the way many roadways were built in America prior to the mid-1930's. Hot tar was sprayed onto compacted gravel to a depth of about 3/16 inch. While the tar was still hot and in a liquid state, small angular chips of gravel were scattered into it. The tar cooled and tenaciously adhered to the compacted gravel base and the gravel chips creating a durable slip resistant driving surface. My driveway is paved in this manner.

Centrally mixed and produced blacktop changed this. Road construction crews began to favor blacktop instead of the hot tar method. There are indeed benefits for new blacktop. As the blacktop industry grew, the tar and chip installers began to disappear. It is a dead craft in many parts of the nation. The same thing is happening in the residential construction industry. Certain tried and true methods of construction are being cast to the wayside.

Become a Believer

I have constructed many, many room additions during my building career. If you want to see how effective water barriers are, then this is the place to learn.

Builders have known for hundreds of years that water and wood don't mix. This is why many of the wood framed houses I worked on had felt paper applied to the sides of the wood structures. This felt paper could be found behind cement stucco, wood siding, asbestos shingles, virtually any exterior building material.

When I would make the connection between the room addition and the existing home, I would have to remove all or part of the exterior wall of the house. Often, I would discover that there had indeed been a leak but the tar paper or felt paper installed by the carpenter 70 or 80 years ago had not only done its job but was still working! Yes, the paper would be very brittle, but it still deflected water. You need to follow this same practice. Install a moisture barrier behind your primary weather barrier material.

A Modern Mistake

There are tens of thousands of homeowners across America who are suffering miserably right now. There are thousands more who will begin to suffer once they realize they have a major problem. Who are these people? They are owners of houses that are covered with barrier Exterior Insulating Finishing Systems (EIFS) or synthetic stucco.

These houses are almost exclusively wood frame construction. The barrier EIFS system consists of a foam panel that is glued to the wood sheathing and then covered with a plastic based stucco that is completely impervious to water penetration. That means it blocks water movement in both directions! Water is getting behind the barrier EIFS and cause massive rot failure to the houses.

This could have all been avoided if the manufacturers of the systems had not discarded the use of a water barrier between the foam and the wood sheathing.

Since these problems have been discovered, a new generation of drainable EIFS products has emerged. These products mandate the use of a water barrier.

Expect advancements in building materials technology in the future. If you decide to use a new material, do a quick reality check to see how the material reacts to known physical laws. Gravity is going to be around for a while. Water is going to rot wood that is not moisture resistant. Remember that tar paper works!

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