looking for creative way to repair/replace rotted floor sheathing at exterior wall 1

[gte447f]

I have a building envelope rehab job where exterior stone/stucco veneer is being removed and replaced because it has been leaking. My role as structural engineer is to diagnose and specify repairs for any wood framing that is uncovered that has been damaged by wood rot (fungal decay) as a result of the leaking veneer. Vertical wall elements like studs are fairly straight forward to deal with, but horizontal members can get tricky, especially members that are part of the floor system at each floor level (this is a 3 story building) and extend well inside the building envelope. They really get tricky when the construction team wants to make all repairs from outside the building without going inside the units. OK, I had worked out what I thought was a reasonable detail to repair rotted OSB floor sheathing at the exterior wall (detail attached), but my detail requires doing work from inside the building. Now I am brainstorming possible solutions that could be installed without having to work inside the building. Anyone care to take a look at the attached detail and offer constructive criticism (go easy please) or offer creative alternatives that could be installed without going inside the building?

 

[msquared48]

I have seen floor ply deterioration extend in from the floor plate with mold present.

How can the contractor assure no mold is present without going inside the unit?

This is a health safety issue, not a financial one.

Mike McCann, PE, SE (WA, HI)

 

[gte447f]

Mike, don't say the 4 letter dirty "M" word. Just kidding. I know it's a concern, but luckily its not my concern.

 

[jayrod12]

I also feel it's fairly unlikely that a single floor joists space will be the only affected area. It's quite likely that the extent horizontally will span multiple bays.

 

[gte447f]

jayrod12, you are right about that. The affected area(s) are often larger than a single joist space, but the idea was to provide a modular solution that could be installed in piecemeal fashion, because one of the issues that becomes a limiting factor if you try to repair a large area all at once is the need to shore the wall above to prevent vertical settlement/deflection while you remove any of the horizontal elements in the plane of the wall, like the floor sheathing, sill plate, etc. The original repair detail as drawn (attached to the OP) could be applied to multiple joist bays side by side, don't you think?

 

[dhengr]

Gte447f:
That’s a real head scratcher. Number 1, that horiz. offset is sure to collect moisture, even if no leaks, just from the potential moisture vapor collection in the vert. void spa. And, you’re right at the latitude here nobody know where to put the vapor barrier. I would say that there may be some damage, not too bad in nature, which can be fixed from the outside only. Is the wood still good, clean and solid, it can be wetted a few times in its life But, a good share of any serious moisture damage will involve interior work and refinishing also. And, the contractor and owner had better adjust their thinking to realize this. The real trick is to make this all as clean and simple as possible, since it must be done, and inconveniences a lot of people who didn’t cause the problem. Unfortunately, this is another one of those cases where the original Arch., builder, specialties contractors, owner, etc., the original geniuses who designed and built this edifice to architectural wonder, should be paying for the mess they made.

For starters, and since they are going to be removing (have removed) the ext. veneer, you should be looking for ways to pretty easily identify the extent of the damage from outside. This is, so you can define the extent and type of damage at each location, and the fix needed at that location. Study, understand and draw the bldg. detail at each location, for further understanding and fix study. Is it a bearing or nonbearing wall, jst. size and orientation, blocking, fl. and clg. conditions, etc. How does lateral load transfer take place at that current joint and your fix? Is there any consistency, so you can literally pick the spots from the outside veneer detail? I’ll bet that cant strip and offset at that fl. level is a big one. You should develop good clean new details for moisture and air movement barriers, flashings, etc. at all these various locations and on the bldg. in general. A veneer system made up of several different materials, different movements, flexibilities, stiffnesses, is just that much tougher to deal with, and flash/caulk at every material change or direction change.

At this stage of the game, you’re in a tough predicament, you didn’t make the mess, you are not a miracle worker, you are trying to make things as clean and simple, consistent with bldg. and health codes, as possible. And, your clients must determine to what level they wish to take the repair. I’m not suggesting leaving moldy sht. rock and carpet in place. Nor can you structurally tolerate spongy 2x’s or wall and fl. sheathing, but, if you stop the water and moisture condensation, you will pretty well solve the lesser problems. If you have significant mold issues, maybe it would be wise to talk with a mold abatement specialist to see what they can solve without total destruction.

 

[gte447f]

dhengr, where to begin?... this building is a mess. For starters, 100% of the veneer, which is either cultured stone or stucco is being removed and replaced. Additionally, most of the exterior OSB sheathing will also be removed and replaced. All of the wood framing that is exposed after removal of the exterior OSB sheathing gets visually observed and probed (by me) for evaluation for decay. Framing members determined to have significant damage from decay are marked for replacement or repair. I have already issued bid drawings that identify the anticipated typical conditions that will be encountered, including the typical members that will have to be replaced or repaired. These drawings were based on a review of the original construction drawings and a preliminary exploratory investigation, where portions of the exterior veneer and sheathing were removed to see some of the existing framing. Where a repair is permitted, my drawings include construction details for the repairs. That is where the detail attached to the OP came from. I am confident that the detail re-establishes the load path, particularly the lateral load path between the floor sheathing and the exterior wall. I am also confident that the detail is constructable, although not easy, but this type of work is never easy. The problem is the detail, as drawn, requires access to the building interior, and although that should have been anticipated by the construction team and building management, there is now push back to construct all repairs from the exterior.

Regarding the existing conditions and load path, the section as drawn pretty accurately represents the existing construction. It is a load bearing wall. 2x4 walls, 2x10 floor joists, 3/4 OSB floor sheathing, 1/2" OSB exterior wall sheathing. For now, assume that the sill plate and other members are good wood, although I assure you that is not the case throughout the entire building, and focus just on the floor sheathing. The floor sheathing is rotted to approximately the interior side of the sill plate, therefore the connection of the floor diaphragm to the exterior wall at the rim board no longer exists. With this particular detail, I am most concerned with re-establishing that connection between the floor sheathing and the exterior wall.

Regarding the water migration and the exterior envelope, you raise many good points. The prime consultant, and my client, on the job is a building envelope consultant, and there scope includes detailing and specifying the replacement building envelope components and materials, so that is not in my purview.

 

[dhengr]

Gte447f:
You might consider using all screws for framing and blocking details, nobody wants to try to drive nails or toenails in that jst. space unless they have access from above or below. If you can cut and renail fl. sheathing from inside, it sure would be easier, faster and many contractor $$ cheaper. That they didn’t see this isn’t all your fault, and if they assumed it could all be done from outside, their thinking may be somewhat suspect. Could you make the cut 16” inside the sill pl. and parallel to it, then jack that old piece out, using the remaining fl. diaphragm as your jacking reaction? It could be your sheathing pulling point too, with a double acting jack. I can help you find and design the jacking system. Contact me at rwhaiatcomcastdotnet so we can talk further. You can’t nail half your blocking and fl. sheathing except from inside. If you can work in 4’ modules (sheet sizes) it would be easier. As a vert. shoring/jacking frame system, consider the following (very sketchy at the moment) and maybe only for that detail. Remove the rim board over the lower wall, use a 6x6x8 or 10’ bearing pc. in its place, atop the double top pl. below, with a 1” chamfer on the 6x6 to miss the sht. rk., maybe. At the next level up, your rim jst., wall sheathing, double top pl. and stud detail should look essential the same as your current sketch, right, although inset 5” or so? You need a ledger/header at this upper rim jst./dbl. top pl. detail, it has a few 3 or 4” long, light 2x3 angles, with the 3” leg horiz. on top and pointing in, and pushing up under the double top pl., maybe screw or two into the bot. top pl. to hold things in place. The ledger might be an LVL or better a light 8” stl. channel, 10’ long, and it gets a few lag screws through its web and into the rim jst. You may need a couple of these ledgers so another crew can be installing the next one, while crew #1 is working on a pc. of fl. sheathing. Now, you need a couple light 3” stl. pipes about 8 or 9’ long and a couple more jacks, and a whole bunch of detailing, planning and implementation notes for the workmen. Red this twist so you get the gist of where I’m going. I think we can flesh it out though. Most times, you can feel the wall sill pl. starting to lift off the fl. sheathing before you can actually see it, then just a little more lift and you should free the fl. sheathing pinching. The contractor is going to go through a whole bunch of recip saw blades.

 

[dik]

Have you looked into using penetrating epoxies... they use them for boat hull repair.

Dik

 

[msquared48]

Good idea dik... that is doable.

Mike McCann, PE, SE (WA, HI)

 

[jayrod12]

I wrote a post but must've closed etips before submitting it. My concern is similar to yours about the diaphragm connection. Depending on how much rot is discovered, you may have enough competent connection left to be ok. Or you may not. And if not, I feel shoring and removal of the bottom plate may be necessary to reconstitute the diaphragm connection.

 

[XR250]

Mike, don't say the 4 letter dirty "M" word. Just kidding. I know it's a concern, but luckily its not my concern.

Some Attorney may think differently. Be sure to contract yourself away from Mold.

 

[r13]

Is section A-A drawn correctly? I expected to see 2 out plan joists, not the 2- 2x blockings shown.

Another question, in what way the rotted sheathing can be taken out without touching the wall above? I think the wall panels need to be removed for inspection, and later for ease of repair.

 

[Ron]

If the OSB rot extends to the inside face of the sill plate, then the sill plate is likely affected as well. I deal with issues like this routinely and going inside the unit should not be a big deal. Yes, it is an inconvenience for the occupants, but can be done in a single day, typically, at each unit.

We did a facade replacement on a twelve story building a couple of years ago. We had the contractor build a temporary wall inside the unit so that dust and debris did not affect the occupants. Worked great. No one had to move out and the contractor finished quickly.

This type of repair is common for 2 or 3 story wood framed condos or apartments with stucco facade. dheng is correct that the offset is a problem for waterproofing. There should be a weep screed detail for this location as well.

Remember...your job is do design a proper repair. Leave the means and methods up to the contractor but don't compromise the integrity of the repair for the convenience of the contractor. A 6 to 12 inch strip repair of OSB under the exterior bearing wall is not an appropriate repair. I would take the OSB inside at least 18 inches and with the blocking you proposed. I would also consider furring the exterior wall out to create a flush vertical surface and provide a proper water resistive barrier behind the stucco with proper drainage at each floor.

I understand that you are the structural engineer for the project, but don't be naive to think that your liability will stop there if it goes south again in 5 or 6 years (Georgia's statute of repose is 8 years, I think).

 

[gte447f]

retired13, yes, section A-A is drawn correctly. What you see in section A-A is (2) existing 2x joists 16" apart with (1) new piece of 2x blocking scabbed on to the side of each existing joist inside the joist space. There is a typo in the attached detail section A-A, in that the blocking should be fastened to the existing joists w/ 2-10d@4" instead of 1-10d@4" as printed. Make sense?

Regarding your second question, about how to remove the rotted sheathing, it is rotten as hell and can easily be raked out from under the sill plate. The good sheathing inboard of the sill plate can be cut out from inside the building. To get a new piece of sheathing in place under the existing sill plate will be more challenging, but I think if the fix is installed 1 joist space at a time, then it will be possible to slide the new piece of sheathing under the sill plate or drive it under with a hammer, removing the rim board and existing blocking below the upper wall if necessary to finagle the new piece of sheathing under the sill plate. Clear as mud?

 

[gte447f]

Ron,
Thanks for weighing in. You mention that you would take the OSB at least 18" inside. My thinking was to take the new OSB back 16" from the end of the joist. My logic was that if this repair is installed in a modular fashion, one joist space at a time, then with 16" joist spacing, the new OSB panels installed will be roughly square with a roughly 1:1 ratio of short side to long side. Other than that dimensional distinction, I take it that you agree in principle with the intent of repair detail I have drawn, specifically using blocking to splice the existing floor sheathing to panels of new floor sheathing and attaching the new floor sheathing to the rim board to re-establish the diaphragm to wall connection and load path?

 

[r13]

gte447f,

Thanks for the clarifications on both of my questions. It is clear and makes sense.

 

[Ron]

gte447f....16" is fine to maintain modular dimensions. Your detail showed the joists perpendicular to the wall which is why I suggested 18".

Yes. I agree with the rest of your approach. dhengr's suggestion of using screws instead of nails is good, though nails will work. Is this project in South Georgia or North Georgia (or not in Georgia!)

 

[gte447f]

Ron, N GA.