Hi Sprucie,
Looking at a variety of imagery sources (my ground survey was during construction), I'd suggest the current modelling is fine - two buildings joined together, which is an almost universal way of representing semi-detached homes.

The separate (but joined) ways allow individual addressing to be added.
In fact, looking at Lane Walk, I've added #1 and #2, and split the shared garage.

building=semidetached_house *might* be better for two units, but as the extra work to tag *only* 2x as semi, means it gets used 4x less in the UK than building=residential.

Hope that makes sense! (and please add more addr:housenumber if you're willing)
Happy Mapping,

James