21 Alderney House, Ferry Court, Cardiff, CF11 0JT

21 Alderney House is a mid-terrace house in Cardiff (CF11 0JT). It has a recorded floor area of 42 m² (around 452 sq ft), construction records dating it to 2003-2006 and council tax band C. The latest certificate (March 2019) returns a B (score 84), comfortably above the UK average. When first surveyed in March 2009 the rating was C, the property has climbed 1 band since. Between certificates, lighting went from Very Poor to Average and main heating went from Very Poor to Average; while window efficiency dropped from Good to Average. Main heating runs on electricity. At 42 m² this is the 4th smallest of 57 units on EPC record in the building, where floor areas span 40–92 m². The building's EPC ratings span D to B, with this unit at the top.

It hasn't traded since July 2007, a hold of 19 years that's notably long for the area. That sale landed at the peak of the pre-credit-crunch market, which is a useful reference point when interpreting the price. At 42 m² it's 25% smaller than the typical home in the postcode (56 m² median across 56 EPCs). Its energy rating outperforms most of the postcode (better than 73% of similar EPCs).