# Sheetrock on the *exterior* of a house?



## rosethornva (Aug 15, 2010)

I'm an old house gal, and know precious little about 1980s/90s construction. I'm helping a friend with a problem she's having at her 30-year-old house in California.

They've found excessive wood rot due to moisture, and she's telling me that her house has sheetrock used as an exterior sheathing (in place of plywood/osb) on her California tract house. 

Has anyone heard of this before? 

And any ideas when this practice was in vogue?

It's on a not-so-nice two-story tract house in a San Francisco suburb. 

Thanks for any insight.


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## rselectric1 (Sep 20, 2009)

Rose, I haven't heard of this practice anywhere around here. But I've been humbled here many times before with geographic differences. 

Is she sure it's actually drywall used as exterior sheathing?

Our California guys will surely be here on this thread to advise.


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## overanalyze (Dec 28, 2010)

Was the sheet rock paper black? I have seen it. Very limited in my area (Ohio), but I think the black paper was a very early moisture coating.


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## Diamond D. (Nov 12, 2009)

My house has it, late 50's. SE Pa.
Water restant, fire retardant gypsum board, that is.

Still used today, although not so much around these parts anymore.
The trend now is more toward insulation board.

D.


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## Dan_Watson (Mar 1, 2008)

We have a lot of that here. Black paper faced.


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## griz (Nov 26, 2009)

Quite possibly part of a fire rated assembly.

Especially in SF.

Bob, weigh in here.......it is after all your backyard:thumbsup:


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## Seven-Delta-FortyOne (Mar 5, 2011)

griz said:


> Quite possibly part of a fire rated assembly.
> 
> Especially in SF.
> 
> Bob, weigh in here.......it is after all your backyard:thumbsup:


I've seen it more in commercial. It's to limit fire spread. I redid the siding on a 4-story commercial building in oldtown, and we installed exterior-rated type-x under the siding.

I live in the boonies, though, so I could certainly see it being used for the same thing in denser, urban areas.





Delta


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## Randy Bush (Mar 7, 2011)

Have resided a couple of houses with it on here. Real pain to deal with when it is rotten. Stuff I have seen was only 2'X8' sheets, wrapped with a black paper. Normally have cut the bad stuff out and replaced with 1/2 osb.

Although I have not run into it yet have even hear of the stuff being used on roofs. guys would step though it when reroofing.


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## jlsconstruction (Apr 26, 2011)

Is it Sheetrock or blue board?


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## Seven-Delta-FortyOne (Mar 5, 2011)

jlsconstruction said:


> Is it Sheetrock or blue board?


Type-X is what we used.

It had a "Exterior Rating", though. Definitely not blue (or green or purple :laughing board.


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## smalpierre (Jan 19, 2011)

How does that work? Wouldn't think it'd give any support to keep the wall from going out of square - diagonal support, isn't that one of the jobs of wall sheathing? Even blackboard is structural if you nail it enough.


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## Randy Bush (Mar 7, 2011)

smalpierre said:


> How does that work? Wouldn't think it'd give any support to keep the wall from going out of square - diagonal support, isn't that one of the jobs of wall sheathing? Even blackboard is structural if you nail it enough.


Lots of time the cornors had ply on them to keep things square.


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## Seven-Delta-FortyOne (Mar 5, 2011)

smalpierre said:


> How does that work? Wouldn't think it'd give any support to keep the wall from going out of square - diagonal support, isn't that one of the jobs of wall sheathing? Even blackboard is structural if you nail it enough.


Missed that in the original post.

The one's I've worked on had sheetrock over plywood.


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## rosethornva (Aug 15, 2010)

Randy Bush said:


> Lots of time the cornors had ply on them to keep things square.


Here are some photos. 

This house was allegedly built in the early 1990s, and repair estimates have soared into the tens of thousands.

And yes, this was used in place of plywood - even at the corners. Strikes me as bizarre, but then again, this *is* Californie... 

Does anyone know what this product was called? And was it in use for very long?


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## rustyjames (Aug 28, 2008)

Exterior gypsum: http://www.americangypsum.com/products/detail/?p_id=137


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## Diamond D. (Nov 12, 2009)

Randy Bush said:


> Lots of time the cornors had ply on them to keep things square.


Or individual 2x4's cut on the angle and placed between the studs as a racking brace.
Or, as I mentioned earlier, with the advent of the insulation board, a metal T strap fitted into a saw kerf cut on the 45* and nailed to the studs.

D.


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## totes (Oct 17, 2013)

Gypsum sheathing is very unfortunate when you are not expecting it. 
I found that on a 70's apartment complex I did a Siding/window replacement for. Same white paper as in your pictures. I have seen the black also..and black that began white...

DensGlass gypsum sheathing by GP is the norm on new commercial around here.


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## TNTRenovate (Aug 19, 2010)

I have seen it around here. Never made sense to me, but seemed like it was an okay method, so I just chalked it up to something that I knew nothing about.


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## skillman (Sep 23, 2011)

Mostly a fire rating thing I would think . Its done a lot on tight lots , fire breaks in zones , subdivisions residential .


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## smalpierre (Jan 19, 2011)

Diamond D. said:


> Or individual 2x4's cut on the angle and placed between the studs as a racking brace.
> Or, as I mentioned earlier, with the advent of the insulation board, a metal T strap fitted into a saw kerf cut on the 45* and nailed to the studs.
> 
> D.


The other guy mentioned plywood corners. Durrr!!! I've seen that done before with blackboard between without being nailed off to where it's structural. I've seen racking braces, but usually 1x and in old houses - inset into the studs.

What I HAVEN'T seen is these t straps fitted in to a saw kerf nailed to studs. What's that look like and how does it work?


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## jlsconstruction (Apr 26, 2011)

smalpierre said:


> The other guy mentioned plywood corners. Durrr!!! I've seen that done before with blackboard between without being nailed off to where it's structural. I've seen racking braces, but usually 1x and in old houses - inset into the studs. What I HAVEN'T seen is these t straps fitted in to a saw kerf nailed to studs. What's that look like and how does it work?


My best way to describe it would be. It looks like the t's from drop ceiling. You snap a line at a 45° and cut the studs so it can slip in. Then pop an 8d nail in through the top of the t into the studs


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## smalpierre (Jan 19, 2011)

jlsconstruction said:


> My best way to describe it would be. It looks like the t's from drop ceiling. You snap a line at a 45° and cut the studs so it can slip in. Then pop an 8d nail in through the top of the t into the studs


link or pic? I think I've got the idea but I could be way off.

Ok This???


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## jlsconstruction (Apr 26, 2011)




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## loneframer (Feb 13, 2009)

We used to use a ton of it along the shore. It has a good flame spread rating. The buildings we used it on were 4' off the property line. http://www.ebuild.com/product-detail/structural-products--systems/gypsum-panels-exterior/223132.hwx


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## mk5065 (May 25, 2009)

rosethornva said:


> I'm an old house gal, and know precious little about 1980s/90s construction. I'm helping a friend with a problem she's having at her 30-year-old house in California. They've found excessive wood rot due to moisture, and she's telling me that her house has sheetrock used as an exterior sheathing (in place of plywood/osb) on her California tract house. Has anyone heard of this before? And any ideas when this practice was in vogue? It's on a not-so-nice two-story tract house in a San Francisco suburb. Thanks for any insight.


A lot of it in South Jersey. 2x8 sheets wrapped in black paper. We call it Gyplap. Don't know if that's the proper term. I've seen people install foam panels over top of it and then install the vinyl siding. I guess that's ok since there are houses that are foam right on the studs then sided over around here. If you remove all the exterior to install plywood then plan on installing new insulation too. I've done it before on a few houses and we always reinsulated. Good luck!


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## mako1 (Sep 1, 2013)

I used it here in IL once on a commercial building built 1' from the property line for fire rating.Code called for 2 layers of 5/8 on the exterior and 1 layer of 5/8 on the interior for a 2 hour fire rating.The wall was 64' X10'H and turned into a $5000 wall for materials.This was around 15-20 years ago.


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## rosethornva (Aug 15, 2010)

Thanks for the many replies and good responses. 

I learned something about new construction today!!!

And frankly, I'm not too dazzled! LOL. I can't imagine putting this exterior gypsum on a house in lieu of sheathing. 

Yikes!

Thanks again.


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## Kent Whitten (Mar 24, 2006)

Rose, while this is not perfectly normal sheathing, it is definitely a common sheathing out west on buildings like multi unit apartments. We called it gyp board. At the time, they said it was a requirement for the prevention of spreading fires. 

It looks like from the pictures that it's not the gyp board that is the issue, but rather the leaking from the siding. Protected from the elements, this product is no worse than anything else that is put up. I've put up tons of it.


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## Eaglei (Aug 1, 2012)

Used 5/8 green board for fire rated sheeting on these semi attached homes today. It's used for code here and sometimes over 1/2'' ply . If not sided soon it will begin to break down . Great when used in a flood or coastal area .

These homes replaced homes damaged or destroyed by Sandy on Staten Island . They are on raised foundations as per new flood elevation maps . Neighbor hood very slowly coming back .


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## aptpupil (Jun 12, 2010)

Yup, seen it before on a 1961 house in Santa Cruz. Did a stucco patch and was surprised to see it used as sheathing. Effing sucked trying to get the stucco off without destroying the gypsum sheathing behind it.


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## CarpenterSFO (Dec 12, 2012)

I've only seen gypsum board used as sheathing in the Bay Area a few times, under stucco, in some less fancy suburban homes from the 60s or 70s. I've never seen it in the City. DensGlass, which is a bit of a different animal, does get used, particularly when fire rating counts, in multi-family projects.

Never in shear walls. Now, many urban and suburban lots in densely packed suburbs are narrow, with few window and door penetrations in the long, side walls. Those long, side walls are sometimes strong enough without being engineered shear walls, or so has been explained to me, and that's where you'd see it, both gyp board and DensGlass these days. That's where I've seen it, now that I think of it.

I'll ask the next S.E. I talk to.


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## CarpenterSFO (Dec 12, 2012)

What do you know, I have a set of plans on my desk right now, for an addition, that specify gypsum board under stucco. Tomorrow I'll ask the engineer why.


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## CarpenterSFO (Dec 12, 2012)

CarpenterSFO said:


> What do you know, I have a set of plans on my desk right now, for an addition, that specify gypsum board under stucco. Tomorrow I'll ask the engineer why.


I asked, and the engineer's response was that the wall needs sheathing, primarily as backer for the stucco, and the wall doesn't require the strength of plywood, and gypsum is cheaper than ply. I can use ply if I want, at about $25/sheet, or gypsum sheathing, at $14/sheet. I'm not sure where score and snap and screw compare in cost to skilsaw and gun nailing.

It was probably mentioned by another post, but gypsum sheathing is very similar to but is not the same as standard gypsum wallboard, which is for interior use only.

One on-line reference mentioned that gypsum sheathing can be used in Type 1 and Type 2 construction, where plywood can't be used.

Rose, I'm glad you started the thread. It's been educational for me.


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## rosethornva (Aug 15, 2010)

CarpenterSFO said:


> Rose, I'm glad you started the thread. It's been educational for me.


Thanks! 

Heaven knows I've certainly learned a *lot* in the last couple days about contemporary construction techniques! 

BTW, this house I posted about is in a San Francisco suburb, and I see you're in that area. I wonder if exterior gypsum board is more prevalent in that area? 

Here in Norfolk, I've never ever never heard of exterior gypsum being used on a house.


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## 91782 (Sep 6, 2012)

smalpierre said:


> The other guy mentioned plywood corners. Durrr!!! I've seen that done before with blackboard between without being nailed off to where it's structural. I've seen racking braces, but usually 1x and in old houses - inset into the studs.
> 
> What I HAVEN'T seen is these t straps fitted in to a saw kerf nailed to studs. What's that look like and how does it work?


Simpson Strong Tie:

http://www.strongtie.com/news/industry/wall-bracing/conventional.html#

http://johnotvos.wordpress.com/2010/07/25/interior-wall-erecting/

Good stuff.:thumbsup:


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## CarpenterSFO (Dec 12, 2012)

rosethornva said:


> Thanks!
> 
> Heaven knows I've certainly learned a *lot* in the last couple days about contemporary construction techniques!
> 
> ...


I don't really know if it's more prevalent; I work primarily in the City, where I've never seen it. I can say that right now, many of the commuting homes built within 75 miles of SF in the 80s, 90s, and early 00s seem to be falling apart, sinking, racking, cracking, peeling, leaking, collapsing, etc.


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## loneframer (Feb 13, 2009)

smalpierre said:


> The other guy mentioned plywood corners. Durrr!!! I've seen that done before with blackboard between without being nailed off to where it's structural. I've seen racking braces, but usually 1x and in old houses - inset into the studs.
> 
> What I HAVEN'T seen is these t straps fitted in to a saw kerf nailed to studs. What's that look like and how does it work?


We've used T braces in the past, as well as coiled strap by Simpson. The coiled straps were installed in an X configuration, wherever we could fit them on a wall. The T straps couldn't be overlapped due to design, so we alternated direction so that a minimum of one would be in tension while another was in compression. We always installed as many as would fit in the wall, which was typically 52 - 56 feet long, depending on the lot size.


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## tedanderson (May 19, 2010)

They have it on this older apartment complex in my area built in the 60's. They have had a lot of fires over there too.


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## Needles (May 18, 2012)

smalpierre said:


> How does that work? Wouldn't think it'd give any support to keep the wall from going out of square - diagonal support, isn't that one of the jobs of wall sheathing? Even blackboard is structural if you nail it enough.



Let in bracing should be used.


In the 90's installed a lot of that ext type x on condo/apts buildings while framing. Would use it in combination with osb.


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## Tom Struble (Mar 2, 2007)

one i've run into recently..notice the fancy wiring


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