Massachusetts. It had a more conventional appearance than the "Saskatchewan House", and also received extensive publicity. Publicity from the "Saskatchewan House" and the "Leger House" influenced other builders, and many superinsulated houses were built over the next few years. These houses also influenced Wolfgang Feist when he developed the Passivhaus standard. Retrofits It is possible, and increasingly desirable, to retrofit superinsulation to existing houses or buildings. The easiest way is often to add layers of continuous rigid exterior insulation, and sometimes by building new exterior walls that allow more space for insulation. A vapor barrier can be installed on the outside of the original framing but may not be needed. An improved continuous air barrier is almost always worth adding, as older homes tend to be drafty, and such an air barrier can be important for energy savings and durability. Care should be exercised when adding a vapor barrier as it can reduce drying of incidental moisture or even cause summer (in climates with humid summers) interstitial condensation and consequent mold and mildew. This may cause health problems for the occupants and may damage the structure. Many builders in northern Canada use a simple 1/3 to 2/3 approach, placing the vapor barrier no further out than 1/3 of the R-value of the insulated portion of the wall. This method is generally valid for interior walls that have little or no vapor resistance (e.g., they use fibrous insulation) and controls air leakage condensation as well as vapor diffusion condensation. This approach will ensure that condensation does not occur on or to the inside of the vapor barrier during cold weather. The 1/3:2/3 rule will ensure that the vapor barrier temperature will not fall below the dew point temperature of the interior air and will minimize the possibility of cold-weather condensation problems. For example, with an internal room temperature of 20 °C (68 °F), the vapor barrier will then only reach 7.3 °C (45 °F) when the outside temperature is at −18 °C (−1 °F). Indoor air dew point temperatures are more likely to be in the order of around 0 °C (32 °F) when it is that cold outdoors, much lower than the predicted vapor barrier temperature, and hence the 1/3:2/3 rules is quite conservative. For climates that do not often experience −18 °C, the 1/3:2/3 rule should be amended to 40:60 or 50:50. As the interior air dewpoint temperature is