Awall with wood studs has fiberglass insulation between the studs. the insulation has r = 21.1 and the wood r = 9.7 (usual units). the studs occupy 18% of the wall area. what is the overall r for the wall and studs? wall studs are usually placed 16 or 24 inches apart in a woodframed home. these wood pieces are called “two by fours” or 2” thick and 4” width. they are actually 1.5” by 3.5”. for the wall considered here with 18% stud coverage is the spacing 16 or 24 inches apart?