Thread: Vapor barrier not required w/ Hardi Plank?

I'm trying to help out a friend. He has a 1994 home with Hardi plank siding. On a recent door replacement job, the crew informed him that the builder did not install moisture barrier behind the Hardi Plank. He called me for an opinion, and I referred him to the Hardi web site, where it said that the barrier is required. The builder did an investigation, and said that a certain kind of OSB was used that does not require vapor barrier. What say ye?

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Ask the builder to produce the documentation on the OSB that doesn't require a vapor barrier. I have a feeling he won't be able to. He probably just tried to cut the corners and skip a step. There may be a type of OSB out there that doesn't require a vapor barrier, but I am not aware of it.

The Product generally requires a vapor barrier.

http://www.jameshardie.com/pdf/hardiplankinstall.pdf

Originally Posted by Eric Laney

....The builder did an investigation, and said that a certain kind of OSB was used that does not require vapor barrier. What say ye?

Did he also use a "certain kind" of sealant at all the joints between the sheets of OSB? Sounds like BS to me. As Jim said...document!

Eric,
Welcome to the board. Will you please finish filling out your personal information so that we know where you are? Sometimes it makes a difference in how your questions are answered.

With respect to this question, I think the answer as to whether the builder has violated the manufacturer instructions or voided the warranty is answered in the link you provided. That is, the local AHJ will determine if the OSB is enough of a weather barrier. Of course, this assumes that there is OSB at the sites you mentioned.

Hardiplank can be installed directly to the studs, with no OSB behind it when appropriately braced studs are on 24" centers or less IF THE AHJ PERMITS IT AND IF ANOTHER WEATHER BARRIER in compliance with local code is present.

Likewise, Hardieplank can be installed over OSB in the absence of any "additional" weather barrier (TYVEK, etc) IF THE AHJ APPROVES IT.

What cannot happen is for Hardieplank to be installed without approved weather barrier.

Have you tried contacting the local AHJ and asking about your particular house? How about calling Hardie and asking one of the engineers?

What I'm getting at is that it is not an issue of if ADDITIONAL weather barrier is a good idea. I see it as two questions.

• Is the builder required to put addition weather barrier? The AHJ can answer that.
• Would the addition of what you are thinking of as weather barrier be a significant improvement ovr how the builder installed it? I can't answer that. Maybe the folks at Hardie can.

Thom is also addressing one requirement more correctly than the others are.

Hardieplank *does not* require a "vapor barrier", it requires a "weather-resisting barrier" (WRB).

A WRB is more of a water and moisture resisting barrier than a vapor resisting barrier, and it also serves, when installed correctly, as a drainage plane for water and moisture get behind the siding, as will happen.

A WRB is, to varying extents, a "vapor retarder", but not a "vapor barrier".

When addressing problems to builders, it helps to use the correct terminology, otherwise, the builder can simply way you are wrong, wait while you defend yourself and stand your ground, then pull out the installation instructions and show your client, the inspector, whomever, that, no, a "vapor barrier" *is not required*.

It is then up to you to change gears and say 'what I meant was', and right there is where you will likely lose your case to the builder, inspector, client, etc.

"What I meant was ... " should be exactly what you said, having said it correctly.

According to the 95 CABO 1 & 2 Family Dwelling Code, a water resistive barrier (WRB) is not required behind hard board horizontal lap siding. The same is stated in the 2000 International Residential Code (IRC). A WRB is required in the 2006 IRC.

So...Is Hardi-Plank considered to be hard board horizontal lap siding?

Travis

Originally Posted by Travis Grubbs

So...Is Hardi-Plank considered to be hard board horizontal lap siding?

No, Hardieplank is a cement board product.

Hardboard is ... well ... like Masonite/LP/whatever else "hardboard" (pressed paper product).

Jerry:

I know the difference between Hardi-Plank and Composition Board Siding. My question: "So...Is Hardi-Plank considered to be hard board horizontal lap siding?", was directed toward the IRC's use of the term Hard Boad Horizontal Lap Siding.

Travis

Originally Posted by Travis Grubbs

Jerry:

I know the difference between Hardi-Plank and Composition Board Siding. My question: "So...Is Hardi-Plank considered to be hard board horizontal lap siding?", was directed toward the IRC's use of the term Hard Boad Horizontal Lap Siding.

Travis

Travis,

Again, no. Based on your question.

Hardieplank is not a 'hardboard' siding. That's like asking is Hardieplank is considered to be wood horizontal siding.

I think what you are meaning to ask is, correct me if I am wrong, 'Is Hardieplank considered to be a horizontal lap siding?', without using the modifier for 'what type of horizontal lap siding', i.e., hardboard, wood, etc.

I think you are referring to 'is it included here?': (underlining is mine)
- R703.3 Wood, hardboard and wood structural panel siding.

- - R703.3.1 Panel siding.

Joints in wood, hardboard or wood structural panel siding shall be made as follows unless otherwise approved.Vertical joints in panel siding shall occur over framing members, unless wood or wood structural panel sheathing is used, and shall be shiplapped or covered with a batten. Horizontal joints in panel siding shall be lapped a minimum of 1 inch (25 mm) or shall be shiplapped or shall be flashed with Z-flashing and occur over solid blocking, wood or wood structural panel sheathing.

- - R703.3.2 Horizontal siding.

Horizontal lap siding shall be lapped a minimum of 1 inch (25 mm), or 0.5 inch (13 mm) if rabbeted, and shall have the ends caulked, covered with a batten, or sealed and installed over a strip of flashing.

If that is the question you are asking, the answer is 'No, it is not included there.'

With a follow up of 'It is included here:'
- R703.10 Fiber cement siding.

- - R703.10.1 Panel siding.

Panels shall be installed with the long dimension parallel to framing. Vertical joints shall occur over framing members and shall be sealed with caulking or covered with battens. Horizontal joints shall be flashed with Z-flashing and blocked with solid wood framing.

- - R703.10.2 Horizontal lap siding.

Lap siding shall be lapped a minimum of 1-1/4 inches (32 mm) and shall have the ends sealed with caulking, covered with an H-section joint cover, or located over a strip of flashing. Lap siding courses may be installed with the fastener heads exposed or concealed, according to approved manufacturers’ installation instructions.

That puts a different spin on the installation of Hardieplank as the joint treatment IS specified in the code as 'one of' the following: "shall have the ends sealed with caulking, covered with an H-section joint cover, or located over a strip of flashing.

Hardi Plank is in a general catagory called fiber cement. Fiber Cement may not have been listed as a general siding type in building codes in effect back in 1994. I'd have to check but it is found in the 2006 IRC so installation details today may be as Jerry Peck quoted.

In 1994 I think that OSB was still listed as a "weather resistive" panel and therefore a "weather resistive barrier. " WRB, the code language now days is Water Resistive Barrier and a WRB was not required by codes to be installed over OSB at back then. APA has changed their code reports and installation recommendations since then and now recommends that a WRB be installed over plywood and OSB sheathing and also, behind plywood shiplap joint siding. So now, if sheathing was used under the Hardi (lap or panel) APA would recommend a WRB.

So, in 1994 the builder was probably complying with code and allowable installation details of the manufacturers of the siding and OSB sheathing. Today, building codes require and OSB (or plywood) sheathing manufacturers would recommend a WRB.

Hope this helps

Mike,

It does help, and it also shows the continual growth and changing of the codes as new materials come along, and an new data and knowledge learned from past installations come along.

The codes are always outdated in that aspect as the new materials and knowledge learned from past installations. In this respect, the egg (the new material and information) must come before the chicken, as the chicken then decides which eggs to keep and which to throw out for the benefit of the next generation.

There's a closely related discussion of this on the APA blog:

APA Blog for Professional Associates: Help Desk Question: Is Building Paper Required by Code?

We are seeing a new type of OSB that has a coating on it to make it a WRB. What I have seen is Green and the joints are all sealed with a 4" wide mastic like tape. It is called ZIP System. I have a whole subdivision that is built like this with brick veneer. Seems to be working.

I took a couple of pictures of a home that was built with it.

I wonder how long that tape will be in place?
Looks like it is already loose in places.

Scott,

Why on earth didn't they install that OSB horizontally instead of vertically?

I know it's OSB and not plywood, but still ...

Originally Posted by Mike Drorbaugh

There's a closely related discussion of this on the APA blog:

APA Blog for Professional Associates: Help Desk Question: Is Building Paper Required by Code?

Thanks, Mike.

Originally Posted by Jerry Peck

Scott,

Why on earth didn't they install that OSB horizontally instead of vertically?

I know it's OSB and not plywood, but still ...

I don't have a clue. My guess was that it was to save on the amount that they used or so that the joint seams would match. I even asked the AHJ if he had a issue with it and he said, "Nope". I'll be marketing new home warranty inspections in a few months in this area. I'm betting on wet walls in several of the homes.

Originally Posted by Scott Patterson

I even asked the AHJ if he had a issue with it and he said, "Nope". I'll be marketing new home warranty inspections in a few months in this area. I'm betting on wet walls in several of the homes.

Structurally, with OSB, it can be installed in either direction, unlike plywood, which should be installed face grain perpendicular to the supports. That is, structurally for the OSB.

However, structurally (for the structure) there is more shear value (I would think, I'm not an engineer) to the wall with the panels installed horizontally (long dimension horizontal).

I'm not an engineer, but I did stay at Holiday Inn ...

Both OSB and Plywood are stiffer/stronger when applied with the strength axis perpendicular to supports. Generally, OSB is stronger than plywood and plywood is stiffer than OSB, except for 5-ply plywood that is both stiff and strong.

Generally, wall sheathing is applied with strength axis parallel to supports (the wall studs). In this manner, the panel is blocked on all 4 sides so it gives the best racking resistance for wall bracing. Usually, the ability to withstand loads normal to the walls are not an issue with plywood and OSB so this works. The advantage of applying horizontally from a practical standpoint is the panel will resist buckling if edges get tight. Engineered shear walls always have blocking on all sides unlike diaphragms which can sometimes be engineered as "unblocked diaphragms," roof sheathing and floors are good examples of unblocked diaphragms.

As bracing panels, the horizontal application gives about 1/2 the racking resistance of panels installed vertically. If you block the horizontal joints then the racking value is the same.

According to the IRC (R602.10.7 exception) in Seismic Desin Catagories A-C for single family homes it is no necessary to block the horizontal joints of Method 3 bracing panels (plywood, OSB). But, as mentioned, this gives them about 1/2 the bracing resistance as panels with blocked joints.

Mike,

Thanks, that's the reason I typically see the panels installed horizontally with the edges blocked. The same racking strength as if installed vertically, but more resistance to buckling. (If I understand you correctly.)

I've also seen, while I was down in South Florida, plywood installed vertically (parallel with its supports) with blocking at the mid point. That would (if I am reasoning this out correctly) make the plywood equally as resistant to buckling as if installed horizontally (perpendicular to its supports). Thus, if blocked at the edges (horizontally installed) or at the mid-point (vertically installed), both would have the same strength, stiffness and resistance to buckling, if I understand you correctly.

Also, I've always been told (apparently erroneously) that OSB was equally strong whether laid parallel or perpendicular to the supports.

Thank you for your information.

I've had Building Officials try to explain why installing it the way it was installed was okay, but they could not, probably because they did not know the reason either, just that 'this is what I learned in class'. At least now I understand why (or think I understand why) that is okay.