I’m working on a deep energy retrofit home in the Chicago suburbs (climate zone 5).

We’re finishing up a front porch that is technically outside the air barrier and thermal layers of the home itself. The porch will be fairly tightly air sealed as WRB (Solitex Mento) goes on sheathing and Intello goes on the ceiling to hold cellulose. The debate is about ceiling and wall insulation.

Even though the front porch space will be used nearly year round, for the vast majority of the time it will be unconditioned space. There will be a fireplace inside the porch (if electric around 4k Btu’s; if gas potentially around 20k Btu capacity), and the stone floor will have a heating mat offering additional Btu’s.

The porch is on the north side of the home. The 3 exterior walls (2×4 framing) are predominantly glass (about 90%). We were going to do R-13 for the walls (likely cellulose), and around R-50 for the ceiling (less out over the double top plate; again, cellulose), and there’s already about R-40 under the slab (used up leftover EPS on site).

It was always assumed that the wall and ceiling R-values would be closer to conventional construction than Passive House for the porch. However, since it’s mostly unconditioned and there’s no ERV do we potentially introduce a moisture problem in winter/spring by combining air tightness with insufficient R-values in the 3 exterior walls? Would it be better to forego ceiling/wall insulation altogether to avoid a potential problem? Or will the ceiling/walls have ample time between uses of the fireplace to dissipate any potential moisture build-up in the walls? The reality is, during winter, the space will likely only be heated 5-10 hours a week (maybe 20 hours occasionally?), otherwise it’s outdoor space in terms of temperature/humidity.

So go ahead and insulate ceiling/walls, or is it safer to skip the insulation? If we insulate, how much risk for moisture build up in the 3 exterior walls?