[qc_riderfan87]

I'm planning to insulate the ext. walls in my old house and the house is framed with 16'' oc 2x4s, tell me if you think this plan would work.

Flash spf wall cavities for air sealing using home kit
attach 1"-1.5" polyisocyanurate to the studs using plasti-cap nails or screws
blow in cellulose insulation behind the foam board
tuck tape foam board joints
attach 1x furring strips vertically at 16" oc
1/2" drywall
cold climate

[Windows on Wash]

You planning on the foam to the outside or inside?

If you have the walls open, just use batts or wet spray cellulose. Dense packing is great for an air barrier but if you are going to seal up the walls with SPF, it isn't necessary.

No need for the air space either.

[qc_riderfan87]

can i use batts after the 1 inch of cc spf ill only have 2.5 inches of the cavity left before i put the foam board up. its a big house and i want it tight and insulated, very cold winters here and strong winds. open cell spf i dont know is that as expensive as the cc??

[Windows on Wash]

There is no reason that you could not.

Make sure with all these combinations of foam and foam board that you don't created a vapor trap.

[Gary in WA]

What is the finish siding?

Any plywood, OSB?

Gary

[qc_riderfan87]

to fit wouldn't the batt have to be compressed thereby reducing r-value

[qc_riderfan87]

Originally Posted by GBR in WA

What is the finish siding?

Any plywood, OSB?

Gary

shiplap sheathing on the outside and stucco. (all insulating to be done on inside)

[Windows on Wash]

I would put XPS or non-foil faced ISO against the ship lap, spray foam all the seams and the connections to the framing.

Fill the rest of the cavity with a high density batt or roxul.

Air tight drywall.

[Gary in WA]

Originally Posted by qc_riderfan87

can i use batts after the 1 inch of cc spf ill only have 2.5 inches of the cavity left before i put the foam board up. its a big house and i want it tight and insulated, very cold winters here and strong winds. open cell spf i dont know is that as expensive as the cc??

----------------

Not a good idea for R-value loss: https://docs.google.com/viewer?a=v&q...SFjptmqEXxrdKQ

With all the foam board in the cavity, the first condensing surface will be inside the f.b., though you will still get a whole-wall thermal loss due to the conducting studs (thermal bridging). This leaves the exterior sheathing colder without the house heat going through the cavity to prevent mold with an exterior water leak or moisture wicking from the stucco (moisture reservoir).

Where are you located?

Gary