Slab insulation – do I understand the code requirements?
Question about slab insulation. The current slab has zero insulation on each side. That was no issue until now because it always an unheated garage. The slab is just that, a slab. No footing, no drainage.
Living in zone 5A and using the table Martin gave me in another thread I conclude I need:
– R-10 on the edge. –> 2.38″ EPS or XPS*
– R-30 on top of the floor indoor. –> 7.14″ EPS or XPS*
*= I use R4.2 for both EPS and XPS because I will use reclaimed foam. From what’s I’ve understood XPS outgasses and it’s R-value drops to that of EPS over time.
Polyiso can’t be used under grade. The floor is likely to cold to put polyiso on top of it. Because it’s old reclaimed material I use an R-value of 5.
I’m aware the exact R-value are a big debate. Often a flame war it seem. I’m not looking for that. I just want to know I really need those values. Do I understand the code correctly?
Do I really need R-10 slab edge AND R-30 floor?
Or is it a bit similar to wall where I need R-20 in the stud bays OR R-13 in the stud bays and R5 continues sheeting?
When reading various sources, including this forum, there seems to be agreement that the edge insulation gives most bang for a buck. And some advise R15 for my zone – 5A.
My problems are:
– R-30 would be a very thick insulation, but I think it’s effective.
– The slab may be hard to insulate?
Attached the dimensions of my slab. Red is concrete. Blue is grade. Ground doesn’t, and can’t slope.