ROI and comfort gain of deeper walls when using ZIP R6
Retrofitting a porch, 23’x15’, sloped roof, to create a four-season room. Three exterior walls, lots of glass (continuous rows of windows and patio door, with knee wall and wall spaces at the two gables). The house is from the 1970s, with 2×4 walls filled with fiberglass; the roof is R49. Yet, the new four-season room has its own roof, which will have either a nominal R38 closed-cell spray foam or exterior plus interior insulation (for an R value yet to be determined). The windows will be good dual pane, but nothing crazy in terms of U factor (unfortunately).
The new room will be connected to the rest of the house with a 6’ open door. It will have, however, its own heating and air conditioning, with a dedicated one-zone mini split.
The current structure is built with 4”x4” posts and double 2”x4” top and bottom plates. My initial plan was to reframe for 6” walls, using Zip R6 sheathing on the outside. A couple of contractors have said that the added costs for materials and labor would not be worth it, and that I should stay with the 4×4 and 2×4 framing. It’s not that I will be able to use much of the existing, but, for example, the top plate on the longest side could remain; the job would be a bit easier. And every 2×6 is more expensive than every 2×4; etc.
I wonder whether, in my situation, there is a noticeable ROI from the extra expenses of having 6” walls (plus the R6, 1.5” sheathing). AND I wonder if staying with 4” walls (plus the R6) would mean a loss in COMFORT. Under either scenario, my plan is to work on air sealing personally, using excellent tapes and the like. The insulation in the walls and in the floor, also, is a part of the job I would like to take care of myself, so as to detail things very carefully.
Comfort is a major consideration for me. If I have nothing to gain in that respect, I’m tempted to stay with the 2×4 framing. Unfortunately, the township wants to know such details at this time; otherwise, I’d be giving myself more time to think about this, and calculate costs.
Any thoughts? Thanks!
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