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Community and Q&A

Preventing wall rot – new construction

lw7 | Posted in GBA Pro Help on

In PA I’ve undertaken a renovation project on a 110-year-old home. The original structure is stone/brick and stucco and the kitchen/bath addition (constructed 50-70 years ago?) was built from lumber.

The kitchen and bath existed on a rotting wood beam foundation and severe water and termite damage was present in the foundation and walls, which buckled. I demo’ed these two structures and the underlying foundation.

A new concrete block foundation was constructed and framers rebuilt the the kitchen (on the first floor) and bath (on the second floor.) The problem is that this new two story structure, in the back of the house, sits adjacent to the original structure without being tied in with joists or bolts. Two of the additions walls are exposed to the outside; one wall sits adjacent to the old structure; one wall borders a neighboring twin property.

My first question is: How best to connect the two structures (original home and new construction) to prevent racking?

In addition, since the property is a twin, the new kitchen wall that sits adjacent to the neighboring property was framed approx. 1/2″ from the neighboring concrete block and brick wall (the size of the gap varies from top to bottom.) The gap that exists isn’t covered by the roof, which followed the framing lines. So, I’m left with a gap that can’t be sheathed with Tyvek (the framers used 2X4’s covered with plywood) because it’s inaccessible, yet water, snow, etc. can enter this gap between the two homes and rot my new structure. How can I reconnect the twin properties and close this gap?

Is it necessary to tear down this wall (difficult, since the second story structure sits on it) and rebuild with other materials or can the gap be sealed via another method that provides a water barrier? Can the roof line be adjusted to cover this gap on the second floor? I have limited time (with bad weather approaching) and don’t know how to proceed.

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  1. GBA Editor
    Martin Holladay | | #1

    It's hard to visualize this issue from your description. Perhaps you can take a photo and post it.

    At the time that your new addition was built, it would have been a relatively simple matter for the framers to attach studs to the existing masonry wall of the older section of the house, thereby tying the two structures together. It sounds like they failed to do that.

    It should be possible to install screws to attach the stud closest to your old house to the existing masonry, without tearing down the addition. You may need to open up access by removing some drywall on the inside or plywood on the outside. It may be necessary to install a few shims between the closest stud and the old house when these masonry screws are installed.

    If you have a crack on the exterior of your house between the old building and the new addition, the crack can be covered with spray foam, high-quality caulk, metal flashing, or siding, depending on the size and location of the crack.

  2. heinblod | | #2

    Expanding gaps are to be filled with expanding material, the standard material is NOT spray foam or caulk but " expanding foam strips " or " expanding foam tapes ".

    Here a few samples:

    Since they might be off-gassing use a product designed for interior use and exterior use.

    Bolting a new extension onto an old brick wall will lead to structural problems, the bolts and/or the bricks will crack.
    Contact a civil engineer.

  3. lw7 | | #3

    Thank you Martin and Hein for your interest in my question. I've attached two photos that attempt to show the issue. First, the framers didn't make any attempt to attach the one wall where the new lumber construction meets the original portion of the house (which was built from rock and brick and covered with plaster.) I haven't proceeded with drywall yet, so the framed structure is open and clearly visible. I'm not sure whether I need to bring a structural or civil engineer to the site to review how to best "join" the two structures. I've been told that spray foam and other insulating materials will absorb moisture over time and rot the plywood exterior (especially since the exterior will eventually have a stucco finish.) Picture 0506 shows this wall from the exterior. My pressing concern is the framed wall the sits against the neighboring property (pic. 0615 and 0612- in close up.) The neighbors wall is cement block and the broken brick wall is what remains of the original kitchen side wall. The framers built two stories adjacent to this wall. As you can see, the plywood exterior sits close to the brick and can't be covered with Tyvek or rigid foam exterior insulation (since it can't be accessed.) Obviously, the plywood can't remain unprotected and rain and snow can and will readily enter this gap from above. I'm stunned at the incompetence of the framers that were hired and the architect that failed to address these matters, in advance.

  4. lw7 | | #4

    apologies...the pic. above of the side kitchen wall (adjacent to the neighboring property) loaded sideways and the other two photo file sizes exceeded the allowable upload size on this site.

  5. GBA Editor
    Martin Holladay | | #5

    I have reloaded your photo, right side up.

  6. GBA Editor
    Martin Holladay | | #6

    If the crack is open to the weather from above, then someone needs to call a roofer. What type of roofing is planned for the area above the crack? If the ledge is narrow, it needs to be covered by metal flashing, sloped to drain.

    Concerning the vertical areas that will be covered with stucco: when a plywood-sheathed wall is covered with stucco, you need (at a minimum) two layers of WRB (for example, asphalt felt) between the plywood and the stucco. Better yet, you need an air gap as well as two layers of WRB. (For more information on this issue, see To Install Stucco Right, Include an Air Gap.)

    You wrote, "I've been told that spray foam and other insulating materials will absorb moisture over time and rot the plywood exterior." Whoever told you that must not understand basic moisture management principles. It is certainly possible to apply stucco to a wall in a way that keeps the spray foam and insulating materials dry. However, many contractors get these details wrong. If your contractors are in over their heads -- and they may be -- you need to hire a competent engineer or architect who understands these issues.

  7. lw7 | | #7

    What can I do about the exposed plywood wall that sits adjacent to the neighboring property? Will it have to be torn down to sheath the plywood? The roofing was already completed and followed the framing on the second floor. The photo here shows the cracked brick wall (that extends to the length of the first story)...there isn't any roofing surface here.

  8. GBA Editor
    Martin Holladay | | #8

    Please explain what you mean by "the exposed plywood wall that sits adjacent to the neighboring property." Is your house attached to the neighboring property? Or is there a gap between your house and the neighbor's house?

    If there is a gap, how wide is the gap?

    Assuming there is a gap between the two houses, I would say that the plywood wall sheathing shouldn't be exposed. Every wall needs an air barrier, a water-resistant barrier (WRB), and a layer of siding to protect the sheathing.

    You wrote, "The photo here shows the cracked brick wall (that extends to the length of the first story)...there isn't any roofing surface here." If the top of the brick wall is exposed to the weather, it still needs to be capped. A roofer should be able to install metal flashing to cap the brick wall. The flashing should be watertight, and should drain to a location away from the building.

  9. lw7 | | #9

    Hi, Yes, there is a gap between the unprotected plywood wall and the neighboring property. The picture shows this gap. Due to the brick being cracked along the length of the wall, the gap is as small as 1/4" in some areas and approx. 2" in other areas. I'm aware of the correct air barrier and the double layer requirements for stucco but, since this wall won't be visible it won't have stucco. It will require a WRB and I'm not sure what else. My primary question is, since the wall can't be accessed, is there any other way to protect the plywood, since placing a WRB would require tearing down the structure?

  10. GBA Editor
    Martin Holladay | | #10

    OK, I think I understand now. Your house is touching the neighbor's house. It's either a duplex or one unit in a row house. The photo shows the gap between your house (sheathed with plywood) and the neighbor's house (the brick house). Is that right?

  11. lw7 | | #11

    Hi, The house is a three story twin. The new construction (an addition in the back of the property) is within 1/4" to 2" from a portion of the neighboring property. The plywood can't be accessed because it's 1/4" to 2" from a cement and brick wall. The only way to WRB the plywood would be to tear down this part of the structure, which also supports the framing for the bathroom (on the second story) to apply the water/vapor barrier. I was looking for alternatives to tearing down what I just had framed.

  12. lw7 | | #12

    What I was trying to say is that the exterior of the plywood can't be accessed due to only having 1/4"-2" of space to work in...the wall would need to be torn down to be able to wrap the plywood with Tyvek.

  13. GBA Editor
    Martin Holladay | | #13

    You need to negotiate with your neighbor. Ideally, your neighbor will allow you to install flashing to cover the crack between the two buildings. The flashing will be tied into your WRB (above your neighbor's house) and will continue onto the roof of your neighbor's house (to waterproof the crack from above).

    To be sure that you have a good air barrier, you'll need to work from the interior of your newly framed wall, using sprayable caulk or spray polyurethane foam.

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