I have a lath and plaster house (as far as I know there is no vapor barrier in it). The house has rough stucco on the outside. I'd like to remove the stucco, then put on sheets of blue rigid foam insulation and vinyl siding. I'm hesitant to do the other three outside walls in the same fashion because the inside wall of the wall that's already been done sometimes feels moist during the winter months. Do you think the blue insulation is not breathing and that condensation is forming inside the wall? Do you think I'll get rot inside the wall? Do you think I should use sheets of white (rather than blue) foam insulation to finish the? Is the R-factor with white as good as with blue?
Answer:
The blue rigid foam appears to be acting as a vapour barrier and its on the wrong side of the wall. On the other walls, try rigid fibre of the same thickness. The wall you've already insulated this way will probably rot out eventually unless you move the vapour barrier to the heated side of it.
