Adding rigid insulation to inside of solid masonry walls–electrical box details?
We have bougt a house (1950s Cape Cod style) with solid msonry walls (4″ CMU inside, 3.5″ concrete brick for the exterior wythe). We’re planning to add 2 1/4″ of XPS to the inside of the exterior walls, and I’m looking for the most practical way to get the receptacles to the new interior surface.
Walls will be 1.5″ XPS adhered to plaster, 3/4″T x 3″ furring strips 24″ OC, 3/4″ XPS between the furring strips, 1/2″ drywall, so a total of 2 3/4″ added to the inside of the wall.
My initial plan was to just use extension rings onthe existing receptacle boxes, but:
1) I can’t find 2 3/4″ extension rings
2) It’s probaby not great to have a metal thermal bridge all the way to the cold masonry (and resultant condensation in the electrical box/wiring).
Would you just mount a new, fresh box to the new furring strip, displaced a few inches from the existing box, connect a short length of Romex to the wires in the old box and running through a cover/knockout on the old box to the new box? (the old box and cover gets covered with XPS)?
Thanks for any tips/ideas.