House was built in the late 70's. Not sure what the R value is. I will have to go up in the attic and crawl space to see insulation. Will be replacing the Andersen double pain windows and Sliders this summer. Other wise house is good. My back of the house faces south east,so I have the same amount of sun in the winter as in summer. I will probably redo the insulation underneath the house while I'm running gas pipe and removing the old well system.