Can I add foil backed foam board to old house?

[luckey]

I want to reside a 1960 era house. It has insulation in the 2X4 walls. I want to add a 3/4" foil backed foam board to the out side prior to installing vinyl siding. Will this cause a moisture problem? Is this recommended? I am also replacing the windows so I know I will have to make the jam extensions.

[Tom7227]

When I had my house sided with steel siding about 15 years ago I had them put in an inch of the pink polystyrene or whatever it is called. We had taken off all the old siding and were down to the builtright material that was on the house. There was maybe 3 inches of kraft faced fiberglass in the wall caveties. They had to shim out the windows and doors before they put on the trim. It added an incredible amount of insulation and it is over the entire surface. I think the area with 2x4's only has an effective insulation of R3 or something like that and so I got an R11 or 12 on the whole thing. I would highly recommend it to you. I'm not sure you would have to pay the premium price they get for the foil faced cause I don't know what that adds to you.

[luckey]

Tom, I plan to replace all the windows so there is no issue with shimming. I will just cut the proper jam extension inside. The main reason to use foil backed is then you don't have to use house wrap. Just tape the seams and your good. I guess if wrap is required, then it doesn't really matter because I either use foil backed, or wrap which have the same effect.

[RoosterR]

Extruded polystyrene works just as fine. Cheaper then thermax/foil faced, but more r value with thermax. Extruded has r 5 per one inch. The main thing is to check what siding manufactor wants to see behind siding. We use 1 inch extruded for sheating and use to tape the seams as you said and worked just fine, but siding manufactures want to see house wrap behind siding. I would suggest a house wrap that way if problem in future u did what the siding manufactor wanted.