In Wales, no this isn't likely a problem. However, due to temperatures staying near-zero it can be worse on a structure if it's regularly cycling below freezing at night.
I wouldn't trust the retaining wall if it wasn't at least 20" of masonry when it's laterally unsupported. Flagstone walls here with lime mortar, laterally supported on floor and ceiling cope at around 14" thick, at which point they can support 6' 11" (by the municipal bylaw) of earth, his walls are laterally unsupported, and by law here can't support more than 3' 11" (if built with a strength equivalent to 8" of 15 Mpa poured concrete, locally about a 14" flagstone wall). Well drained soil will help, but when you're building a wall into the face of a hill, you're being stupid and putting your house below-grade.
I seriously expect this house to fail in a bad winter. I would trust this house in warmer climates, but definitely not in anything colder. I'd also like to know if this guy got approval by a structural engineer, because I certainly didn't read it when I glanced over.
I wouldn't trust the retaining wall if it wasn't at least 20" of masonry when it's laterally unsupported. Flagstone walls here with lime mortar, laterally supported on floor and ceiling cope at around 14" thick, at which point they can support 6' 11" (by the municipal bylaw) of earth, his walls are laterally unsupported, and by law here can't support more than 3' 11" (if built with a strength equivalent to 8" of 15 Mpa poured concrete, locally about a 14" flagstone wall). Well drained soil will help, but when you're building a wall into the face of a hill, you're being stupid and putting your house below-grade.
I seriously expect this house to fail in a bad winter. I would trust this house in warmer climates, but definitely not in anything colder. I'd also like to know if this guy got approval by a structural engineer, because I certainly didn't read it when I glanced over.