in the process of building a new house and trying to figure what i want to wrap it with. im thinking of using 3/8 fan fold, i think its about r1.8. is it worth using? and if so what sould i tpe the seems with? trying to stay away from foam board(rmax), very expensive. any advise appreciated.
If it is open cell foam(that lets moisture thru), it is probably OK. Every bit helps. But closed cell foam will trap moisture inside the wall cavity, not good. Tyvek is still probably the best housewrap. It lets moisture pass out but not in. It also depends on where you are located. Insulation and moisture barrier requirements vary depending on climate.