GENERAL PASSIVE HOUSE RETROFIT INFORMATION
Retrofitting a house to become a Passive House is a challenge. It is not impossible, but you are often limited with conditions that you are either unable or unwilling to change or are too expensive to change. Does this mean a retrofit is out of the question? Of course not. The same care and planning that goes into a New Construction project will be brought to a retrofit project with a few exceptions. Your house is already sited. Chances are you are not going to want it jacked up and turned 10degrees so that it makes better use of the sun. It may be sitting on an uninsulated slab foundation. Your consultant will take all these factors and more into consideration as the retrofit plan of your home takes place. Some projects may be a simple energy upgrade without changes to the shape of the house. Other homeowners may decide now is the time for that addition. In either case, the existing home will be measured and a plan will be developed so that the changes will take advantage of the natural environmental benefits that are available, and minimize the detriments (that north facing single pane picture window has got to go!)
The easiest type of retrofit will entail placing insulation on the outside of the building and then cladding over the top of that. Some buildings may not be able to have their outside facade changed (such as historical buildings). This will require an even more stringent type of retrofit since adding insulation to the interior walls of a house means moving electrical boxes, working around a myriad of internal corners, and having to be extra diligent not to introduce conditions that could lead to mold. This type of retrofit has been achieved in Europe and can be done here, but it will mean extra planning and diligence.
I have visited two Passive House retrofits, one a full Passive House project, one that was working towards being a phased project (only part was completed now with plans to complete the rest at another time. This is not an officially recognized practice in the US, though it is in Europe.) Both projects added insulation to the outside, the completed project added insulation over an uninsulated slab and then placed a floating floor above that. The roof of that house was raised to meet the physics necessary to be a passive house, but it did manage to pull off one of the most remarkable Passive House feats – a 16foot wide North facing sliding glass door. That architect definitely did not settle for a 2 story box!
Your project may have other things to consider, but you will understand what the issues are and how they will be addressed prior to the project beginning. Your house will be modeled and the Consultant will know that it is expected to operate at the Passive House standard. What will remain is to make sure the changes are made in accordance with the plan and that any issues that arise during the process are dealt with immediately.