Is there any way to flatten 1/2 in OSB sheathing that has warped due to getting wet? My contractor left the sheathing without house wrap on for several weeks and consequently, all the sheathing is bowing out between the furring strips. The renovation included adding exterior insulation to the house so the contractor added 2×4 members every 24 inches to minimize thermal bridging. Each bow is perfectly centered at that 24-inch spacing. Any help would be much appreciated as the contractor has asked me how to fix it, not a great sign I know.
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Maybe. If I understand this discription.
Adjust depth to run cuts up the 2x4, pull nails as necessary (maybe 1 side of the cut only). Allow to flatten, re- nail.
The furring strips has me confused?
Interesting. So leave one side attached and trim the other end to fit when it’s flat?
Sorry for the confusion, the furring strips are the 2x4s
Not exactly sure of this situation when I posted earlier.
If the osb was bowed it was because it was installed tight to each other.
Admittedly I don’t know of many installers gap it on install .
So the solution I suggested might help flatten it out.
Maybe.
So you’re building exterior walls outside of this brick house?
How thick is your insulation? Are you doing rain screen siding? Is the insulation under the 2x4s or between them? 1" insulation on warped OSB, between 2x4s might leave enough clearance to provide the ventilation needed to qualify as rain screen. Kind klunky, but...
2x4s are pretty heavy for furring- most people use 1x3 or 1x4, but 2x4 might work in your favor in this case.
The insulation is 3" thick Closed Cell Spray Foam. Initially, it was not going to be a rainscreen installation as the contractor was unfamiliar with it. It looks like it will now be a rainscreen to use the stand-off battens to compensate for the irregularity of the OSB. I attached an image to clarify the assembly a bit. The house has some brick facing, and the bottom story is CMU with stucco rendered over it. The plan was to apply external insulation over the entire assembly. The contractor wanted to use spray foam over other vapor-open insulation, and wanted to use only dimensional lumber for speed and simplicity. The insulation is ~3in thick. Then the OSB was hung over that. That is where the bowing is occurring due to the OSB getting wet multiple times. There is currently a house wrap over the OSB, I left it out for clarity.
Nice pic- it helps make sense of everything. 1x3 furring and "rain-screen" siding installation seems to be a reasonably good resolution to the bowed OSB (and rain-screen is a good idea anyway.)
There are several issues it would be good to work out with your contractor before proceeding, in the hope of avoiding more surprises. Search the FH site for good siding practices.
1) Insect proofing the top and bottom of the rain-screen cavities- Cor-a-vent is one good option.
2) Dealing with the transitions from 1st to 2nd floor.
3) Dealing with installing, flashing and trimming doors and windows, while maintaining air circulation.
4) Trimming inside and outside corners
5) Trimming and flashing hose bibs, dryer and fan vents, receptacles, lights, DHWH & HVAC vents. Discuss how to maintain good air circulation above & below trim.
6) Help the contractor understand it's standard practice to prime all 6 sides of each piece of siding. Discuss good caulking practice.
Remember that since you have closed cell foam on the outside, your walls will have to dry to the inside, so there can't be any vapor barriers inboard of the foam. Make sure the brick and CMUs can dry if they accumulate condensation.
Thanks for the feedback. Unfortunately, I don't know how open to discussions the contractor will be, but I will give it a go. Am I right in assuming that 1-6 applies to the trim and siding in regards to the rain screen function?
The siding is LP Smartside. On examination, it looks as though the back is not covered in primer. I could be wrong. It might just not be readily obvious. Is that something that LP would stipulate? Or is that something extra?
I checked the LP site and found they DON'T recommend priming the back side of SmartSide, ref https://lpcorp.com/blog/all-about-exterior-paint-for-lp-engineered-wood-siding
This varies from standard recommendations, but in general, the Prime Directive is "Follow the manufacturer's instructions." They're usually not going to be too far wrong AND, you at least won't void the warranty.
Ref discussions with the contractor, between the power of the purse and the contractor's previous screw-ups, I'd say you have the upper hand, and that you should feel comfortable using that power judiciously. It's your house and you'll be living in it for a while.
Ref issues 1-6, these are all places vulnerable to water intrusion and the devil is in the details. You and your contractor need to think like a drop of windblown water. Search the FH & JLC websites for a rain screen and flashing education.