Resheathing an outside wall

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  #1  
Old 09-17-16, 05:51 PM
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Resheathing an outside wall

Residing a wall of our house. 7ft high, 40ft long. 7ft is living while the other 33 is garage. One window in the garage (only one on the whole wall) that is being replaced due to age and needs reframed due to a rotted out sill and no jack stud. The interior of the garage is osb - wanting to go drywall and 'finish' it.

The 33 ft exterior is two layers of 1/2 poly-something (polyisocyanurate maybe) foam. I originally just thought it was 1 sheet and was surprised to find two. I had assumed they used osb interior as the structural support so my plan was to remove all of the exterior foam and replace it with osb (picked up the zip system osb this afternoon). Since, as I mentioned I wanting to remove the interior osb and replace it with drywall.

Now that I just found two layers I am wondering if I should continue with my plan and remove it all or if I should leave the bottom layer and put the osb over that.

The second photo is siding, foam, foam, [missing] bottom sill.

There are some water trails on the inside cavities (removed the R-11 fiberglass).
I was going to use roxul R-15 to replace the batts.

SW MO.

Thoughts?

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  #2  
Old 09-18-16, 05:37 AM
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Yes, OSB on the exterior is more common especially when doing vinyl siding as it provides a continuous nailing surface. In your case I think someone was trying to get smart and put the OSB on the inside to "finish" the garage and get more insulation by putting it on the outside. These days that would not pass code especially since the garage is attached to your house.

The streaking on the back side of the insulation may have been there from construction. Or, it may be from condensation since that foam sheeting is acting like a vapor barrier and trapping moisture trying to leave the home. It condenses on the sheet and runs down.

I would remove the siding and foam sheeting from the exterior. Completely sheet the exterior in OSB. Wrap the wall with a breathable house wrap like Tyvek. Then re-install your siding.

After the exterior is done I'd remove every bit of the OSB in the garage. It's a fire hazard. Insulate the walls. Then hang your sheetrock and at the minimum do the first layer of mud to seal the joints.
 
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Old 09-18-16, 07:35 AM
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There are many innovative ways to build a wall assembly, but when they try something new they often fail to follow established science, as pilot says, and they lack the test of time. You do have a mess there and it raises the question as to what else they did. Are all of the walls in the house like that??

Installing rigid on the exterior of the house is common, but I usually see it going over plywood or osb, related link below. But proper framing and air sealing are also required.
Musings of an Energy Nerd | GreenBuildingAdvisor.com

Hard to determine, but the small soffit and what looks like the bottom of a header in the first picture look out of place. I'm thinking moisture (leak or condensation) ran down the bottom of the roof deck and then down the inside of that wall creating those streaks. Does the foam insulation extend up tight to the bottom of the roof? With no venting moisture from vehicles will condense on that roof as it has no other place to go.

Bud
 
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Old 09-18-16, 08:56 AM
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Thanks guys.
Fortunately it's just the garage addition that was done like that (it's horrible as a whole). The rest of the house is done right.

I'll crawl up into storage and see if I can see where the foam extends to.

Pilot - glad you confirmed most of my plans.

Bud - what is striking you odd about the soffit and header? The header is for the window. Although to me I think it's too high being right against the soffit so I am planning to lower it a couple of inches to actually get some siding above it. Should I do something different with the soffit? I want to do this right the first [second] time


One tricky part will be placing osb behind the soffit without removing the soffit. I just had new gutters installed so not really wanting to have to remove them.
 
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Old 09-18-16, 10:44 AM
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In this link: http://www.dos.ny.gov/DCEA/pdf/Energ...insulation.pdf
You can see some of the traditional ways to frame an overhang. If you look at 12.4 or 12.6 and cut the overhang in half or less the bottom of the soffit rests against the top plate and a decent size header would extend well below. Your picture shows the bottom of the header flush with the bottom of the soffit. Not sure what they did to accomplish that, very small header, very steep roof, deep cut for rafter (bird's mouth) or what.

Since you know the sill plate rotted out and you can see the stains from water flowing down, the conclusion is that water came from above. A leaky roof would typically leak in just one area, but condensation would/could be the entire roof. I've actually seen a half inch of ice form and later melt.

What is there for other venting in the garage, ridge vents, gable vents, or other soffit vents? Since they went to the effort to insulate as they did, I suspect zero ventilation and that is a huge problem in a cold climate if there is a source of moisture.

Bud
 
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Old 09-18-16, 12:33 PM
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"Not sure what they did to accomplish that, very small header, very steep roof, deep cut for rafter (bird's mouth) or what. "

My thought is they ignored their true life calling.
But... It's a very steep roof and they only used a 2x4 header over a 42" opening with NO jack studs.
I will be bracing the ceiling and replacing it with a 2x6 with jack studs. So that will lower the header plus I may nail a 2x4 flat on the bottom of it and lower the window even more.
Will that make the soffit attaching less unusual? It will from my understanding of 12.4 and 12.6 diagrams.

I did some more looking and I am thinking they used 2 layers of foam to get the addition on the same depth as the house. The house has old pressed siding under the vinyl but since I will be removing it also, I should be good with just one layer of sheathing across the whole length. It should all line up and be level/flush.

Venting. About that. So the roof has a ridge vent but I never understood why since there are no soffits vents.

So what do you think of this plan:

1. Reframe window with correct size header
2. Remove ALL exterior foam sheathing
3. Remove the back soffit 'bracket' and remove the soffit by sliding it down
4. Install OSB right against the studs all the way top to bottom
5. Replace the solid soffit with perforated
6. Fasten the soffit bracket back (may get creative but I've got some ideas)



Would #5 help with the condensation? In the long run I need to install baffles up in storage to go all of the way to the ridge but would the perforated be a step in the right direction in the meantime? I'd say within a couple of years I'll do the baffles.
 
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Old 09-18-16, 01:03 PM
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First we don't know the original source of the moisture. If the original occupants were parking cars in there to allow the snow to melt or worse added some heat to melt it faster, then as long as you don't do that the major moisture issue is gone.

The perforated soffits sounds good.

Baffles all the way up may not help as they will fill with cold air and slow the air flow. Plus, you want the incoming air to mix with inside air and get pushed out the top.

Is the garage heated in any way, other than solar gain?

Make sure the ridge vent is open. Sometime the roofers cover it with underlayment and forget to cut it open.

Are garage doors well sealed or are they providing some air flow?

Bud
 
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Old 09-18-16, 01:15 PM
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I don't believe the previous owners did anything unusual but it's possible.
No heat aside aside from some poor insulation between house and garage which will also get some roxul.
Thanks for all of your help, I'll proceed with that plan.

Hopefully last question that I know is asked a million times -

2x4 walls. Roxul r15. This will be in the garage exterior wall, the stretch that has living space behind it, and the wall between garage and living space.
Add 6mil vapor towars living space or not? Same for the garage exterior?
I seem to read as many for it as against it.
 
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Old 09-18-16, 01:35 PM
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Old thinking was vapor barrier to the warm side in all climate zones. new thinking is they are only needed in the far north and deep south. Everywhere inbetween they can be omitted. The catch is, the house should be well air sealed and when retrofitting an existing home that is difficult to determine. I see no harm using a vb on the warm side for the living space but no need for one in the garage.

As for the previous owner doing something unusual, parking ones can covered with snow inside is normal, but bad in a poorly vented garage. Solar gain plus the insulation would produce humid air and result in condensation and frost on the bottom of the roof deck.

One visual indicator would be looking at any nails that protrude through the roof. If they have been getting frosty the area around them will be discolored. Of course, if the entire roof has been suffering from condensation it may also be discolored, blackish.

Bud
 
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Old 09-18-16, 08:22 PM
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Not quite done

I failed to answer your other question - the garage doors are pretty well sealed I'd say but they do have 1-2 inches on either side at the bottom where the bottom seal doesn't extend all the way to either end.

I crawled behind the short kneewall in the storage part (the part over the garage addition) to take a look at the roof sheating.

There is r11 all the way from the top (I can't see past the kneewall but safe to say it goes all the way) to the bottom where it's bunched up a little. I pulled back on the bunched up part and was able to stick my hand down to feel the soffit.
The sheathing/deck looks like new. No discoloration on the five or so cavities I checked out - focusing on the ones above the problem window. I wasn't really able to see any nails sticking through but I did see a couple staples ends (tar paper I assume) and they looked shiny. All of the nails connecting the rafters to the ceiling joist are looking really good also.
I can also see the bottom layer of foam coming all the way up to the rafters (second layer starts under the soffit as seen in the photo).

So what I am wondering is: should I mess with something that seems to be working?
Granted, I don't know what caused the water stains on the back of the foam.
The window had absolutely no flashing on the sill and the exterior flashing didn't have any sealing so I have no doubt that and what looks like old termite 'crusty stuff' is what caused the bottom sill to rot away.

So would it make sense to leave the solid soffit, cut the first layer of foam about an inch below the soffit, attach the osb beneath that and then tap the gap between the foam and osb - again, using the zip system and the must-be-made-of-gold zip tape.

My reasons for doing this are 1) again, the roof deck looks great so afraid changing the soffit might affect this; 2) starting the osb an inch beneath the soffit shouldn't have any affect on the current soffit/roof deck relationship; 3) naturally, it's the easiest as it doesn't require removing and reinstalling the soffit

#3 isn't a strong reason either way but it's a reason none the less.

Also for what it's worth I will be foam sealing (the foam gun) all along the inside cavities against the studs. Not sure how much this matters but I will be doing it.
 
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Old 09-20-16, 10:42 AM
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Hey Bud,
Any thoughts on leaving the solid soffit after finding the roof deck looking new?

Hate to bump the thread but hoping to get started on this tomorrow.

Thanks
 
  #12  
Old 09-20-16, 11:20 AM
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With the source of the moisture still unknown it is difficult to say. But any location that gets well below freezing and has a moisture issue will get frost on those nails and discoloration around them, which you are not seeing. Your call, but sounds like the lack of soffit venting isn't part of the issue. If more low venting is determined to be necessary in the future, it can be installed almost anywhere in a garage.

Bud
 
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Old 09-20-16, 12:12 PM
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Thanks. Yeah, I know it's tough to make a call given the limited picture I've painted.
I have to run a network cable the entire length of the garage behind the kneewall I was in so I'll do a more extensive check. If it all looks like new then I'll leave the solid soffit otherwise I'll replace it with perforated.

Appreciate all of the help!
 
 

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