Weather-proofing issue, how to proceed?

[Miranda Crown]

I have a friend who is renting an apartment with what sounds like either serious weather-proofing issues or burst pipes and she is not sure (nor am I) how to proceed. Before they moved in, they were told that someone broke into the apartment and deliberately flooded the toilets/sinks, etc. but were told all was fine. Since they have lived there, corners of their walls ice up and now have mold, the laminate flooring is buckling and shifting. They have asked their landlord to address and been dismissed. Is their next step a lawyer? Any other ideas? Thanks, in advance!