huangyhg

damaged shear wall, or lack thereof
ok this is kind of complicated so bare with me as i attempt to communicate this as technical as i can.

the south wall line of this residential home has cracking indicative of wind or seismic damage. around all opening are considerate cracking larger than what would be called "serviceable".

in particular is a 20-ft section of wall that is 15-ft in height from bottom plate to top plate. this 22-ft wall section is composed of two 8080 sliding doors with a 3-ft plywood shear wall on either side. the header above these two 8080 sliders appears to be out of plane, at least 10 or so degrees. around these openings are what i would think are severe cracking (1/8" -3/8", sometimes even 1/4" wide) extending out diagonally from all corners of the openings, as well as cracks horizontal and vertical. there is spalling in areas. the wall also deflects/vibrates a fair amount when pressured by my hand.

the roof above this wall is a cathedral type. there are no ties at all - roof or otherwise. the 4x10 rafters simply land on the top plate.

now, aside from the obvious lack of shear walls, and possible lack of ties anywhere on the 15-ft high wall, my question is thus; the interior of this wall (drywall) shows no evidence of cracking at all. the drywall interior side of this wall looks smooth with no cracking - i can't even see visual cracking. i asked if the interior drywall has been repaired or repaired recently, and i was told no.

is it possible to have one side of a wall damaged considerably and the other side in perfect shape?

what is the cracked material?
this does occur sometimes but usually with more minor cracking.
more common explanations:
1. interior wall is more ductile than outer wall (i.e. timber interior wall and masonry outer wall)
2. interior wall is more free to expand/contract due to joints at openings e.t.c. and lack of restraint at ends.
3. the exterior wall being stiffer is taking much more load than the inner wall.
i am sure there are other possible causes.
wall is typical residential construction. stucco w/ 1/2" plywood, 2x4 studs at 16"o.c., and 1/2" drywall interior.
this is a potential insurance project as the client is claiming that this damage was caused by a mini-tornado event.
but upon my inspection i can't tell if this cracking was the sum of multiple extreme events over the course of the structure's life, or from that single mini-tornado event. at first i was convinced when observing the exterior, but upon inspecting the interior drywall i have become somewhat dubious of the cause - not to mention the client's intentions.
cracks radiating out from windows and openings at diagonals, in my mind, is indicative of some type of torsional event....it sounds like the entire structure tried to "rack". what csd72 said on his no. 3 sounds like a very viable possibility. the relative stiffness of the external finish is much greater than the internal, therefore could be carrying the bulk of the load. out of curiosity, is the general shape of the house more square or is it more rectangular??
you have checked the foundations for any evidence of settlement? which would affect both sides of the wall, but they could have redone the interior....
ashleyassociates, the portion of the house in question is more square than rectangular.
i unstersatnd the relative stiffness possibility. i will communicate that to the engineer i bring to the structure.
i do some forensic consulting and most of the time, it is settlement of the foundation. take a look at the slope of the grade. if it is level or sloping towards the foundation, then taking elevation readings at the permiter will confirm the settlement.
i saw a house in louisiana that had some minor looking cracking and the foundation along the perimeter was about 2" lower, and in one corner you could feel and see the 3" drop.
don phillips
mjaret....
the square shape was what i expected you to say. houses that are essentially square are more prone to rack in a wind, seismic, or settlement (as donphillips said) event....and the greater the height to the footprint ratio of the said structure makes an even greater possibility of the racking (especially in residential construction). donphillips suggestion of settlement is definitely the first choice to check as you can get a tangible number from this, and if it has occurred would pretty much close your case other than the reason for the settlement. if settlement is not the primary reason, then your forensics job will probably become more difficult.....i could believe a seismic or a settlement problem....i think that a mini tornado causing a house to rack/deform without catastrophic failure and then rebounding to the previous shape is probably a stretch. good luck
is the cathedral roof applying a horizontal force on the wall in question?
i have recently inspected a couple of cases where the cathedral roof framing is "flatting" out pushing the side wall out. in one case all the movement was on one side, the other side being a little stiffer due to stairs, closets etc.
a substantial ridge beam or collar ties are needed to keep the roof frame from pusing on the side walls. also the top plate of the wall can provide for some horizontal bending if it is so designed.
let me know if this is the possible situation.

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