I'm currently doing a complete renovation to a 1940s double brick bungalow in Toronto. This includes adding a second story addition which is vertically flush with the existing exterior brick facade. The current plan is to spray foam the interior and then clad the exterior with hardie board. I'm considering adding 1" of rigid EPS or GPS insulation under the cladding.
I'm trying to decide if this is a good idea and if the pros outweighs the cons. For instance, adding this will further narrow the space between houses and require the windows to be set back. There will also be some space behind the studs on the existing double wythe walls to allow a continuous insulation application.
Does it make sense to add the exterior insulation even though the interior insulation will be more then sufficient? If so, are there any tips or things to consider when applying the rigid insulation over the existing brick facade?