Hardie Siding/Vapor Barrier


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Old 10-03-09, 01:22 PM
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Hardie Siding/Vapor Barrier

Hi all - I am about to begin a project where I will be removing masonite lap board siding and replacing with Hardie lap board. The Hardie lap board matches the masonite. In some areas of the home I will be replacing some, not all of the board and on one side of my house I will replace all boards. My questions are:

1 - building code says I do not need a vapor barrier (I live in North Carolina). Hardie best practices documents say I should use a vapor barrier. Since I do not have an exterior vapor barrier in place now and it seems to not have done any damage in the 15 years I have lived here, is it really necessary to install a vapor barrier?

2 - If answer to question 1 is yes, then in the situation where I am replacing 6 or 7 boards on one wall, would I also use the vapor barrier? Would not having a vapor barrier on the rest of the wall cause a problem in this situation?

I want to do the job right, but with one week off from work and renting an aerial lift to complete the job (will also be painting the house), I would like to eliminate any task that is not absolutely necessary since time may become an issue.

Thanks for your help.
 
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Old 10-03-09, 02:24 PM
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The 2007 IRC, section 703.1 states that a WRB is required. A water resistive barrier is not a vapor barrier. It is a liquid barrier (such as #15 felt or housewrap). This is required so that if one piece of siding blows off during a hurricane or thunderstorm, the integrity of the building envelope will not be completely compromised, causing more damage to the home than there should have been had a WRB been installed. Windows must also be incorporated (flashed) into this WRB.

The caveat is that James Hardie says a WRB must be installed in accord with "local" building codes. In some cases, local standards are years behind the rest of the country. While there may be many rural areas that have no standards, someone has to set the bar at a certain level or substandard building practices would become the norm. So while a certain set of standards may not be "enforced" in your area, they would properly be called "best practices". The question then becomes, "what standards do you have for your home?" While you may not be doing the entire house at this time, it only makes sense to put the WRB on now behind the siding that you ARE installing.

If time is an issue, Tyvek, Typar and similar materials come in 9' rolls and therefore goes on 3x as fast as felt.
 
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Old 10-03-09, 06:24 PM
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Not sure which part of NC you are from (not in your profile), but Clay and Cherokee counties, near us definitely require vapor barrier on all structures, whether new or remodeling. Not too sure how your mixture of Masonite and Hardie is going to look.
 
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Old 10-04-09, 07:01 AM
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Thank you both for your replies

I am in Cabarrus county, just north of Charlotte. I should have said "it was not code when my house was built" in 1995. As of now, I am not sure what the code is.

Based on your answers I think it will be wise to install the barrier.

As far as looks when mixed in with the masonite, I nailed up a test piece about 4 feet long and painted it. It loooks quite good actually and is difficult to detect unless you knew it was there. (at least that is what my neighbors tell me).

The key thing after getting done with this project will be to keep up with maintainin the masonite.
 
 

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