wall energy code compliance in a major renovation

Hi Ramana, Depending on how much insulation is needed, a 3.5” stud wall can be built 2” to 6” from inside face of the outside mass wall, leaving room for continuous insulation between it and the existing mass wall. Additional batt can be placed in the stud wall as well as electrical. Interior partitions can then butt up against the stud wall leaving the continuous insulation as continuous. The location of the vapor barrier would need to be calculated to avoid condensation. -Kjell From:

Hi Ramana, Your approach sounds good for prescriptive compliance. In MA we have energy code amendments that can alter some of the prescriptive baselines and approaches, so I would check the state code to make sure that your assumption is sound. We come up against this construction type alot in the Boston region on existing buildings that have brick or stone mass facades. For a museum project, and for a lab building renovation in a historic brick building, we conducted WUFI analysis on a lot of different interior wall scenarios. I recommend doing this for the climate your in and the anticipated interior RH so you can see which assembly is the best choice for thinness, condensation risk, etc. That is probably what Kjell had in mind, but a spreadsheet calc for cooling and heating seasons may not give you the full picture of condensation risk if your use type is high humidity like multi-family or a museum use. Good luck! - Alison  

Ramana, You should tread lightly. Depending on climate/code it may not be possible to meet the prescriptive requirements without putting the wall at danger, but it depends on a lot of things –material and condition of the wall, exterior details, roof conditions, window to wall conditions, interior environment (humidity/mechanical), etc. I would not use batts or try to make something up. This article from Dr. Joe outlines the big issues and some successful strategies: https://www.buildingscience.com/documents/digests/bsd-114-interior-insulation-retrofits-of-load-bearing-masonry-walls-in-cold-climates Duane Carter F

I second Duane on this topic & highly recommend to have somebody (insulation vendor would love to do it for you) run WUFI or run it yourself (approach with caution!). We recently completed one particularly challenging retrofit project and the modeling helped to navigate & choose the best options for the project. Lessons learned, bringing the wall assembly up to the current code may do more harm than good in some cases. Good Luck & we need more knowledge & confidence on this topic if we are to successfully retrofit the existing building stocks to capitalize embodied carbon within those buildings! SK