Room vs Outdoor Temperature in an NZ Home

The data plotted here was collected in my bedroom using a "weather forecast multi-channel in-out thermometer with cable free sensor and radio controlled clock" (model TTN302). The data is from the winter of 2011 in Christchurch, NZ. We had recently purchased a house after several years living in Europe and were more than a little shocked by how cold our room temperature was, despite having a heat-pump. Consequently we added insulation to the ceiling (Terra Lana), underfloor (Autex) and a moisture vapour barrier was laid on the ground under the house. A week later the single-glazed windows in the house were removed and replaced with double-glazed windows by Thermoglaz (www.thermoglaz.co.nz). Their method allowed us to retain the character of the original wooden frames. Dates: No insulation, single-glazed: 2011-08-08 2011-08-19 Insulation, single-glazed: 2011-08-22 2011-08-28 Insulation, double-glazed: 2011-09-03 2011-09-26