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Re: T1-11 siding

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Well, most of the T1-11 I see likes to delaminate as it's biggest failure. Straying from the structural issues already discussed, I would suggest great care in placing a rigid, thin cementitious product over a (presumably) failing wood product on a structure which may have only been designed for a flexible covering (L/120, as allowed by residential codes).  Even synthetic stucco (dryvit) requires minimum L/240 deflection limits.

Gerard Madden, SE wrote:

I just received plans to do some minor upgrades to an existing home. The contractor who sent me the plans indicates that they are going to place stucco over existing T1-11 exterior siding on the upper level two levels of the residence as one part of the modifications. I know there are some drawbacks with T1-11 that are escaping me at this point, but IIRC, they are likely due to exposure to the weather. I realize that the increased weight of the stucco (10 psf) to the walls will increase the seismic load, but I don’t think by that much. The home was built to the 1973 UBC.


I’m hoping someone can direct me to some information or can share their thoughts on:

  • Shear values for T1-11
  • Summary of the historic problems with T1-11
  • How to visually observe if these problems are present
  • Suitability of placing stucco over the T1-11


I’m just in the proposal phase at this point, and don’t have much except a few pictures and the original plans. It was 5/8” T1-11, can’t seem to find any nail spacings on the drawings.




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