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Installling Hardieover T1-11 - Any issues I need to know about

Installling Hardieover T1-11 - Any issues I need to know about


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Old 08-25-07, 08:15 PM
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Installling Hardieover T1-11 - Any issues I need to know about

My current set up is the following: A 1 year old addition has studs, OSB, Tyvex and stained T1-11. The original 30 year old house has studs, plywood, black paper and stained T1-11.

I am going to install hardie over the t1-11 (actually hire someone to do it). 3 contractors who have looked at the job and bid it said to keep the t1-11 on the house and that they would just apply hardie directly over the t1-11. I am going to use the prepainted hardie so I know the butt joints will not get caulked and where it hits the trim boards it will get caulked.

Is it not necessary to reinstall Tyvex or some other barrier over the t1-11 prior to the hardie install. Since the butt joints won't get caulked I know water will get behind the hardie. Since T1-11 is an exterior sheating will this be okay as long as it has a place to escape. I will have a trim board running horizontantal at the base of the hardie and then it will be stick on stone under the trim board. I guess I should not caulk the last hardie board that rests on top the horizontal trim board. Thanks
 
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Old 08-26-07, 04:14 AM
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All the advice you have been given and what you suggest is right on. I see no problem in installing the Hardie over the T1-11, and there may be different schools on the Tyvek, but since it is a good vapor barrier, and breathes, I would apply it prior to installing the Hardie. You don't want the possibility of moisture deteriorating the wood underneath the Hardie.
 
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Old 08-26-07, 06:28 AM
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In addition to the recommended building paper substrate (Tyvek) when joints are left uncaulked, you MUST put an additional flashing behind every joint. See figure 2 in their online instructions.

If you have a horizontal board above your cultured stone, it would have a drip cap flashing, a 1/4" gap between the flashing and the first row of siding, and you are right that the 1/4" gap would be left uncaulked.
 
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Old 08-26-07, 12:07 PM
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Why don't you think any of the 3 contractors thought it necessary to add Tyvex over the t1-11 before installing Hardie? I figured they would want to do for the fact they would get paid more. Is Tyvex a wind barrier or a water proof barrier. Some have said having the dual barriers (2 layers of Tyvex) would be bad b/c if moisture got behind the first layer it would never be able to escape. At least that is why I think they say not to do it. I feel it should be done and when I called James Hardie they concurred and if I did not do it I would void the warranty. With that said, I am not going to rely on a contractor who gives me a 1 year warranty void my 50 year warranty with Hardie. I guess I'm just confused why contractors wouldn't think this was necessary in the first place. Thank goodness for sites like this.
 
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Old 08-26-07, 12:27 PM
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they probably feel that since the house already has Tyvek (spelled with a K), adding more would be redundant. But Hardie recommends the Tyvek be the substrate immediately behind the siding... so the safe course would be to follow their recommendation to a T.

Removing the existing siding would be one way to accomplish this. All the nail holes would need to be sealed with Tyvek tape. Or another layer of Tyvek should be installed.

Tyvek can be both an air barrier (meaning when all it's edges have been sealed, it slows air pressure, decreasing air exchange due to wind) and a water barrier (meaning it prevents liquid water from penetrating) but it is vapor permiable (meaning it allows water vapor to pass through it.) Since it is vapor permiable, there is NO chance that it would trap moisture between layers.
 
 

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