When working on the former McKeesport YMCA and Hilltop Community Health Center, despite the benefits of "outsulating", we were limited to insulating from the inside. The buildings' history, character, and detailing were important to their communities and leaving the exterior façade in tact was the most appropriate solution. We paid an energy penalty for thermal bridges and for air-tightness. We tested our brick and that was an additional financial expense. In the end, we were able to drastically reduce energy consumption and retain the building's original character.
There are examples of buildings where the exterior façade is actually a detriment. Although we may loath putting a second skin over masonry because masonry skins equate with low maintenance, there are many buildings that can benefit aesthetically from the facelift that insulating from the outside mandates. Not every problem is solved using this method, there may be some lingering issues in the basement but the vast majority of thermal bridges and infiltration issues are handled thoroughly using this approach. Public housing that was developed in the 1960's comes to mind as a perfect type of building to use the out-sulation approach to reaching Passive House.
At the NAPHN conference Mark Elton [http://sustainablebydesign.co.uk/] presented several really interesting projects in the UK using this technique. The structures were public housing from what many call the "New Brutalist"period in architecture. Those buildings typically have a concrete structural frame that was expressed on the exterior and thermal bridges galore. Those buildings are frequently associated with the failed public housing policies of the sixties and have the same social stigma that they do in the US. In addition, their aesthetics are generally disliked. Elton covered the exterior with a new pre-fabricated wood cladding that sat on a new footer and was craned into place. Elton chose the pre-fab self-supporting exterior skin in wood because of wood's low carbon footprint. Windows were replaced as well as the heating system and all of this was accomplished while the building was occupied without doing a gut rehabilitation project.
At the end of the project the building was totally transformed and the impact of this on the neighborhood was really significant. This presentation changed the way I look at buildings of that era...they all look like candidates for Passive House retrofits to me now.
It also raises the question of when buildings are not good candidates for Passive House. Historic buildings with landmark status and interiors of extraordinary quality are simply not good candidates for the kind of retrofit that Passive House requires. Perhaps we will think about those buildings being served by on-site PV that covers parking areas as a way of mitigating their energy use.