Less efficient was poor choice on my part for words, it’s still efficient, just not a high r value to allow for some heat transfer that inevitably happens anyway. My air barrier is beyond what most do, so even though my r value isn’t really high overall, it’s enough to keep us toasty warm without being expensive - it is technically lower than 2x6 construction, but it’s more energy efficient because of sealing and no thermal breaks. The house originally relied on just fir strips, plaster and paint as the barrier and insulation. What most contractors wanted to do was either go with more r value and get there with sprayfoam pretty much, which was the worst thing we could do for the brick. So our method goes like this from outside to inside — regular brick, air pocket, 9x9 structural clay tiles with webbing and air pockets within, render, air pocket, 1” foam board with foil barrier and finally rockwool insulation and then drywall. The foam board doubles as a reverse barrier in the summer when the house is cooler than outside. The fear of over insulation was a concern because lots of new data suggests that allowing that inner brick to be ‘warmer’ in the winter is how it’s meant to work and why it lasts so long, the same research is showing that allowing the masonry house to breathe is another reason it will last so long. Anyway, in the end, there was way more insulation talk and planning than anyone one of us would of liked but it did save us from spray-foaming everything.