I am building a new house in St. Paul MN area. I have question about above grade wall design. I am swaying towards Exterior Foam board +(OSB) W/ cellulose inside wall cavity, yet I want to know if a built rite or similar product (Exterior) w/ cc spray foam between stud wall cavities would cut down on thermal bridging and simplify the building process and be a better ROI. Trying not to overbuild and find the best wall system for my investment. I will not build a system that does not have a realized return on my initial investment. Thank You

CCspray foam in cavities does nothing to prevent or minimize thermal bridging. Thermal bridging occurs through the framing, not through the cavity. Foamboard is a poor conductor of heat, so putting it outisde the framing minimizes heat transfer. your first assembly ( Exterior Foam board +(OSB) W/ cellulose inside wall cavity) will work well, provided the foam is thick enough. 1/4" or 1/2" won't do it; 1" is better, 2" will work well and (if air sealed) will help reduce your heating cost and improve comfort. this is part of a complete system so you're best bet is to buy and read Builder's Guide to Cold Climates by Joe Lstiburek.

hi hank ..please let us(me) know which way you decide to go. I'm probably in the same county as you and are looking at the same question. It seems the builders would prefer the spray foam but even that they see as over kill, on the other extreme some(many) web sites say we need ~6" of exterior to be "safe" on the extra insulation which most builders think is a crazy idea and don't really want to talk about.
thanks

Thanks for the replies. Pouring footings Friday!! I am leaning towards 1.5 - 2 inches of Exterior foam board w/nailers for steel siding and cellulose inside of wall studs. Foam, Housewrap, OSB, Framing, Cellulose, Sheetrock. Not sure about Net and blow or damp spray cellulose; I would have to see about the pricepoint of the rental equipment.

Hank
I do not have the formula in front of me but depending on the climate zone there is a balance for the foam and insulation ratio inside the wall and outside foam to give you the thermal break.
Also the spray foam in the cavity gives better insulation but even more importantly it is to block air movement, even a bigger energy drain than the thermal break.
So the way I see it if I was using wood I would spray a layer of foam to seal the interior air movement, then finish the cavity fill with fiberglass (fiberglass with air movement is just a air filter) I would put foam sheets on the out side of the OSB sheeting giving you the thermal break.

As you are looking to build a new home I would consider the SCIP system (Structural Concrete Insulated Panel system) The home I built last winter maintained and minimum temperature of 60 degrees.
With the thermostat set at 55 and the daily solar gain the house was incredibly warm. With a lot larger than 25' and a house designed for passive solar with passive solar and smart glass would preform even better.
No matter what system you use thermal mass should be considered.
Check out Oak Ridge National Labs thermal mass/ conclusions

Thermal Mass - Energy Savings Potential in Residential Buildings
Comparative analysis of sixteen different material configurations showed that the most effective wall assembly was the wall with thermal mass (concrete) applied in good contact with the interior of the building. Walls where the insulation material was concentrated on the interior side, performed much worse. Wall configurations with the concrete wall core and insulation placed on both sides of the wall performed slightly better, however, their performance was significantly worse than walls containing foam core and concrete shells on both sides.

Hank
What house wrap are you considering? Most are breathable.

SCIP Panel, I found some information based on my location (Building Science & Fine Homebuilding I think) pertaining to above ground exterior walls. I am going to put 2" foam on the outside of my wall sheating & fill the inside wall cavity with cellulose or fiberglass (Spray fill), I have information stating that I should not put foam on the inside wall cavity because it will not allow for proper drying to the inside. As for house wrap, I am not sure what kind of product would best work with my wall design. Hank