I think you should set the shader to masked rather than translucent. If that broken window is a different material and it shows through I think that indicates a sorting issue with translucency. if that does not solve it you can double check the face normals be setting the shader to two sided. if that looks correct then you…
^^ correct, it is a sorting artefact related to using a translucent material Definitely don't use a translucent material on anything that isn't supposed to be translucent - there is no way to completely eliminate all the possible sorting/lighting artefacts that come with translucency and they are extremely expensive…