Foam Insulation

1. What is the R-value per inch of Johns Manville's AP Foil Faced foam sheathing product?
2. Why is the R-value per inch of polyisocyanurate foam so much greater than fiber glass?
3. Which way does the foil face (reflective side) on the AP foil faced insulation need to face?
4. How can I get a higher R-value in a 2x4 or 2x6 cathedral ceiling cavity space?
5. Can I place two foil faced AP sheathing boards one on top of the other to achieve a greater thickness and R-value?
6. What kinds of nails are used to attach foam sheathing?
7. What fastening pattern (spacing for the nails) should be used when installing the foam sheathing product?
8. Can Johns Manville's polyisocyanurate foam sheathing products be used as structural sheathings?
9. I just purchased some Johns Manville polyisocyanurate foam and want to know why are the edges yellow? Will this have an adverse effect on the product performance?
10. When installing the polyisocyanurate foam sheathing product, do the seams need to be taped? If so, what kind of tape should be used?
11. Do I need to use a housewrap over the polyisocyanurate foam sheathing product?
12. How do I cut the polyisocyanurate foam product?
13. Can I leave Johns Manville AP foil exposed?
14. What are the acoustical properties of Johns Manville AP foil faced foam?
15. Your product literature states that this product can be used under a concrete slab, but not below grade. What is the correct application?