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Discussion Starter · #1 · (Edited)
When our 2-story garage was built in 2006, we didn't have plywood placed outside the joists, and then the Tyvek on the outside of plywood, then Hardy plank siding on the Tyvek. A friend who came by after the garage was built visibly noticed the Tyvek through the joists, and said you "have no support." Thus, I installed R19 insulation between the joists and then 1/2 plywood all the way around the first floor and 2nd floor on the inside -- using deck screws fastened into the joists every 16 inches. The thinking was that, later, if we want sheet rock, we could use 3/8" over the plywood. (for now, don't worry about electrical work, assuming the original electrical works doesn't change).

The garage measures 20' x 30' so the 2nd floor is a large area.

Our new contractor who is finishing the upstairs pulled the plywood off (only on the 2nd floor) because he stated that:

"plywood doesn't breath like sheet-rock, and with a large 10-30 degree temperature differential between the Tyvek/Hardy surface and the plywood during AC usage in summer and heating in the winter, the risk of condensation and hence mildew is very high. Therefore, we should just use 5/8" sheet-rock to act as the support."

Please note that in the attic, all of the weight of the center of the roof bears down on the center of the attic floor, based on vertical joists. There are no vertical joists at 1/4 and 3/4 the width of the attic to distribute the weight.

After removing the plywood that provided structure, we have noticed that some surfaces are not level on attic floor joists (beams).

So the contractor said today that all of the weight of the roof, which is only supported by center vertical joists, is causing the attic floor joists to rotate slightly resulting in bowing/sagging. He then said what really needs to be done is to build a temporary false wall running down the center of the first floor (90 degrees to the 2nd floor joists), and jack that up. Then, on the second floor, build another temporary wall 90 degrees to the attic floor joists, and then in the attic add vertical runner joists at the 1/4 and 3/4 attic-width locations in order to more evenly distribute the weight of the roof. Then, once that is done, nail in short alternating 2"x6" cross boards positioned like "X" between the attic floor joists -- essentially to prevent the joists from rolling and rotating -- which is what will allow them to bow. The cross-members once nailed in when the false walls are in place with everything level will provide tremendous support and minimize bowing of the entire structure.

While this sounds good, I do think a large reason why the garage is shifting is because the plywood I screwed in all the way around the 2nd floor was removed, and the weight of the roof is now coming down harder causing more bowing. Interestingly, if the contractor assumed that 5/8" sheet-rock could take the place of the plywood for support, I think the sheet-rock would eventually split open and the weight of the roof would eventually tear it all apart.

Do you recommend going the route of building false temporary walls on the first and second floors, jacking up the first to level out bowing upstairs and in the attic, and then fasten vertical joists to the roof joists at 1/4 and 3/4 attic-width locations, add alternating cross members to the attic floor joists (looking up from the second floor), and then use 5/8" sheet-rock on the interior walls on the second floor?
 

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Civil Engineer
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I had a lot of trouble understanding what you are trying to describe. Part of the trouble is your terminology, which is not standard. For example, you use the term vertical joist. I have no idea what you mean. A joist is by definition a horizontal structural element typically designed to support a floor. A "vertical joist" may be a post or a column, or could be a truss member, but I don't really know what you mean.

Perhaps if you include some photographs, and maybe a sketch of the framing with some arrows pointing out where you think there is a problem, that would make more sense.
 

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I'm really worried that no plywood was used on the exterior. At LEAST on the corners with some sort of foam board sheeting. As usual, cutting corners trying to save $$$ in the beginning, is going to leave you spending even more $$$ to correct everything.

I'm not sure 5/8" rock will correct the structural problems.
 

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Just a quick few points. Hardiplank can be installed directly over studs with a vapor barrier - and without plywood or OSB sheathing. Hardi provides installation instructions for such conditions.

However, the structure itself would need some sort of shear restraint, like shear panels or let-in bracing. If no shear panels or let-in bracing is present, I question whether the structure ever received a framing inspection.

Your wallet is already open, and you have a contractor. My advice to you is to spring for an extra couple hundred bucks and get an engineer in there to tell you exactly what's going on, and whether the contractor is on the right track. To me, something seems fishy.
 

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JOATMON
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I think I have a pretty good idea of what is going on.

If you are getting bowing of the attic joists due to weight of the roof, I think you have some real serious issues. I'm guessing your 'attic joists' which should also be rafter ties are not properly attached to your walls and letting the walls start to spread out. If this happens, that that 'center' stud going to the peak of your roof that is causing the bowing is having to carry more weight than it should.

To be honest, your garage scares me. Lack of shear wall on the outside. Improper rafter ties, etc.

I'm guessing no permit was obtained or inspections done?
 

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Not sure either what's happening but sheathing is just that, sheathing, it should not be part of the structural integrity of the roof or a wall. The roof and wall should stand properly woot sheathing. Dry wall is no way structural. Please submit pictures of the interior of your roof support system so the experts can weigh in. There are some guys on this discussion group who seem to have considerable expertise in roof systems. Wait for on of them. I am not one of them but I know some of the suggestions from your contractor are sort of suspect.
 

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Not sure either what's happening but sheathing is just that, sheathing, it should not be part of the structural integrity of the roof or a wall. The roof and wall should stand properly woot sheathing.
Sheathing in a wood framed structure built without bracing is a critical element in the stability of the building. It resists the lateral forces brought on by wind and seismic movement. Also, properly installed plywood or OSB sheathing can have 3 or 4 times the shear resistance of gypsum, depending on fastener density. We can't simply write off the lack of sheathing in a wood framed structure, and say it doesn't contribute anything to integrity. Shear resistance has to be baked into the framing, somehow. Whether it be sheathing or bracing, it must be part of the structure. If it's not there, a problem exists.
 

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I just flat out refuse to install any siding without real sheathing under it.
I've seen some with just plywood in the corners and foam board or Cellotex for the rest.
One kick to the wall and you can get in the house.
The sheet rock will be far more likely to have nail pops and cracks.
 
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