Helping Your Home Stand the Test of Time: Weather Resistant Barriers


All forms of exterior cladding leak - siding, masonry and stucco all leak. Whether it is caused by some sort of wind driven water entry, or by a cladding that has reservoir characteristics like a sponge, they all leak. This isn't a bad thing. In a properly constructed home, the water infiltration hits the drainage plane and runs down and out, not a big deal. The big deal is in making sure this drainage plane exists.

If we want to look back at how things were done in “the good ole days”, leaky cladding wasn’t much of a concern. You see, prior to the energy crisis a couple decades ago and the increasingly stricter codes on insulation and air tightness in homebuilding, walls could continually receive large amounts of water and be relatively safe in terms of durability. Those “good ole" walls had the ability to consistently dry out and wood will last a long time if it can continually dry. Think about those old wooden barns out on a farm somewhere, a hundred years old and still standing tall, for the most part.

That all changed when we realized that comfort inside the home could be drastically improved with insulation and air tightness. And who doesn't like a comfortable home? I like air conditioning in the summer and heat in the winter. I also like to keep as much of it inside as possible. So what's the problem? We simply added insulation and removed the draftiness, why do we have to change anything else? Well...now those “good ole" wall assemblies do not have the ability to dry and that is a big deal. We have now created a wall assembly that will not only hold moisture, but lots of it before the problem ever shows its ugly face. So, we have to find a way to keep the water out. We do this by detailing a drainage plane using a weather resistant barrier.

The weather resistant barrier or water resistant barrier, whichever one you want to call it, is there to keep the water out of your wall assembly. You can use house wrap, building paper, tar paper, or Zip wall sheathing (what we at Buraski Builders prefer). Whatever you use, it is second in importance only to the roof to the long-term durability of your home. This isn’t a place I’d choose to save a dollar on, it’s too critical and it's code.

We at Buraski Builders like to use two products specifically for our WRB. Dupont Tyvek HomeWrap has a proven track record with its ability to shed rain water. Really, that is its sole purpose, in my opinion, it is not an air barrier. Not only does it allow water vapor from the inside to escape out, all water vapor has the ability to pass through it in either direction. It's important to understand how a product can both shed bulk liquid water, while at the same time allowing water vapor to transfer through it and why we want this. Seems a little far-fetched, doesn't it? A product that is waterproof yet allows water vapor to migrate through it. However it's actually very simple. You see water vapor differs from liquid water in the size of its molecules. Water in the liquid state is a large cluster of water molecules, in the vapor state there is space in between each molecule, thus allowing it to pass through the house wrap freely. You have to pick your poison here, if you want water vapor to pass through this amazing material that can also shed liquid water, you have to allow for the passage in either direction.

So don't buy into the hype that it only allows passage in one direction. It's not a miracle material. If detailed and flashed correctly over most residential cladding it will perform well. But it's important to know and understand its limitations. We usually want water vapor to be able to pass through our walls freely. This gives our wall assembly the ability to dry. You just need to know when such a product will perform well and when it won't. I don't recommend a wall assembly built with a highly vapor permeable sheathing, such as fiberboard, Tyvek as the WRB, and a masonry type cladding such as brick on the exterior. That's a disaster waiting to happen. Tyvek Home Wrap works really well over a lower permeable sheathing such as OSB or CDX plywood, especially when detailed correctly.

We also like to use Huber Zip System wall sheathing and tape, especially on our new construction projects. This is a really good product. Zip sheathing is a dense OSB product with a resin coating applied to the face at the factory. Once the sheathing is installed in the field, you then tape all the joints with a high adhesion acrylic tape and roll the tape to make the wall assembly water and airtight. It is very simple. Zip sheathing puts the air barrier at the sheathing layer, and this is where I prefer it. You see, unlike Tyvek, a wall assembly with a properly installed Zip system WRB is essentially airtight. There is no extra step, no details to mess up in the field or have a guy forget to do. You just install it per manufacturer’s recommendations, and presto, the water and air barrier is complete. Pretty awesome stuff. Now we have a wall assembly that actually performs the way it should because insulation actually has the R-value advertised and drafts disappear.

Your home becomes more comfortable without going through a difficult process of detailing the air barrier. We don't need to install a layer of closed cell spray foam as a miracle cure for air infiltration, which only putting one inch of that stuff concerns me in our climate anyway, I want two inches, but I digress. Our goal is to build an airtight and water tight wall assembly and Zip System wall sheathing has given us a cost effective way to achieve this. Now once we have this airtight home, other things have to change with it. More on that to come in future posts.

By

Joseph Betz

Construction Manager

Buraski Builders, Inc.