Windows & siding

Old 01-18-06, 05:28 AM
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Windows & siding

Hi again!
We have some windows that are missing vapor barriers and window wrap around them. This may sound like a stupid question, but do all windows (whether they're installed on walls w/ siding or brick veneer) need a vapor barrier & window wrap? We're asking b/c we don't want the builder to tell us that exterior walls w/ siding does not require this. I'm trying to get exact information from the James Hardie website, but I can't seem to verify this.

Thank you.
Old 01-18-06, 02:57 PM
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According to the installation PDF on their website, they say:

"A Weather-resistive barrier is required in accordance with local building code requirements. The weather resistive barrier must be appropriately installed with penetration and junction flashings in accordance with local building code requirements. James Hardie will assume no responsibility for water infiltration."

The only problem is your local code's definition of a "weather resistive barrier". This is defined in the 2003 IRC (International Residential Code), table R703.4. In most cases, I believe that rigid foam (like Dow blueboard) qualifies as a weather resistive barrier, which is why I think most builders don't feel it's necessary to put housewrap over rigid foam.

Housewrap is not a vapor barrier, so you might not want to mention "vapor barriers" to your builder or you'll look like you have no idea what you're talking about. Tyvek, typar, housewrap... use any of those terms instead, because that's what I think you are trying to say when you use the term "vapor barrier". Most housewraps allow water vapor to pass through... what they do is help stop "liquid" water from damaging the underlying substrate.

Rigid foam, on the other hand, is pretty much waterproof, except for the seams. It is a vapor barrier, meaning it will not allow water vapor to pass through it either. As I mentioned, this is probably why the builder feels he doesn't need housewrap. The problem is, if the windows are not sealed to the foam, then water will get into the rough openings, damaging your interior trim, creating a mold problem, and eventually rot the wall and ruin your drywall.

The biggest problem in the window industry is that there are currently no minimum standards in place that control who qualifies to install windows. Currently, any joker with a pickup truck, a ladder and a hammer can do it. The same could be said for window installation guidelines. Mainly, it is the window manufacturer that has a vested interest in whether their windows are being installed properly or not. Contractors SHOULD care how the windows are installed, but many of them only care about which of their subcontractors can do it the cheapest. That usually means that the ones who don't do it correctly- or at least the ones who aren't using the current technology, sealants and window wraps- are the ones who get the job.

As far as building codes go, I believe they are very vague when referring to specific trades. They often refer to "following the manufacturer's instructions" for installation guidelines.

What you would need to do is visit with a local building inspector at your city or county level. Explain the situation and let him know that you'd like to find out if your contractor's building practices are up to code. Specifically, IRC section R703 which deals with exterior wall coverings. Table R703.4 has exceptions which may include the reason why your contractor is able to skip the building paper. City and state authorities have the right to alter or impose additional exceptions to the IRC codes, so you would have to contact your local officials to find out anything for sure. Additionally, you might try contacting the window company, and asking what their "factory certified installation instructions" are for houses sheathed with rigid foam. Then you can see if the contractor followed those window installation instructions or not. I'm just trying to help point you in the right direction.
Old 01-18-06, 03:50 PM
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Some additional research revealed Dow's policy on the installation of their products as a weather-resistant barrier:

In part, a notice at the bottom of that page reads:

The following Dow insulated sheathing products qualify as a weather-resistive barrier (WRB) when installed according to the installation instructions developed for “installation of foam sheathing as a weather-resistive barrier”: STYROFOAM DURAMATE* Plus, STYROFOAM Residential Sheathing, STYROFOAM Tongue & Groove, STYROFOAM Square Edge, STYROFOAM Residing Board, THERMAX*, TUFF-R* and Super TUFF-R* and therefore do not require the use of a building paper or a housewrap as a WRB.

However, to follow the installation instructions, the builder would have had to follow step #6, which reads:

Tape all insulation joints and penetrations using nominal 3” STYROFOAM* All-Purpose Tape (ie. horizontal and vertical seams as well as exterior penetrations from pipes, dryer vents etc.). In the case of exterior penetrations only, seal around opening with an all-weather sealant (ie. silicone caulk, Dow GREAT STUFF™ Gaps & Cracks sealant) prior to taping.

I would almost guarantee that this is where you will find that the builder was lacking. You rarely see the edges of 4x8 styrofoam sheathing taped with an *approved* styrofoam tape, and Dow also specifies that exterior penetrations be sealed with silicone PRIOR to taping.

So according to Dow's instructions, windows (an exterior penetration, as I would read into it) must be caulked AND taped in order to meet the definition of a weather-resistive barrier, in accord with IRC R703. But rather than using Dow's styrofoam tape on your window's nailing flanges, I believe that most self-adhesive window wraps are approved to be used on Dow styrofoam products to seal window penetrations.

So the question would be, does your locality base their code requirements on the IRC, or perhaps codes that essentially have the same requirements as the IRC? I would think that being in a hurricane prone area like Houston that can receive 20" of rain in a short period of time, that they would have some pretty strict codes when it comes to this type of thing.
Old 01-18-06, 05:27 PM
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In addition, you might take a look at the following PDF:

It kind of backs up what I said earlier about checking into the window manufacturer's installation instructions. The window manufacturers have figured out they need to cover their bases... and put it into the hands of the contractor / subcontractor to install their products correctly.

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