I'm replacing my siding and find lots of gaps in the fiberglass inulation
(in-wall). I am thinking of adding foam boards to the exterior walls to
better seal them and add little insulation. Going by R-value, this doesn't
add much (1/2" R4) but maybe this would protect better against winds etc. I
am installing hardie plank siding. Will this home 'breath' ?
ventilation? Anyone has experience with this type of insulation?

Luke