Replace styrofoam insulation?


I’m replacing a 30 year old metal roof laid on 1/2 inch sheathing. This a gambrell roof with two dormers on one side and one larger dormer on the other.

The area I just stripped is a portion of the living room roof. While replacing the sheathing I’m looking at 3.5 inches of what I’d call blocks of styrofoam. These are laid on 24 inch centers. The beads making up the block are the size of bb’s. It takes a bit of effort, not much, to make the material crumble into individual bb’s. The material appears to be in good shape.

My question is:
Should I replace this styrofoam? Is there a more energy efficient material I could use?

I’m hoping for some replys tonight as I must keep working on the roof before the weather shuts me down.

Thanks your help!


We call the white stuff either Beadboard, EPS, or Elastoplystyrene. It is an okay insulation. The R-Value of your 3.5 inch is about 8-10 .

You could leave it on, or you could upgrade the insulation to an ISO board or the yellow foam board which will double your R-Value…but it is expensive.

A good rule of thumb is ISO is half the thickness of EPS with double the R-Value.


Thanks for your input. I’ll look into pricing of the ISO board. The effected roof area is about 1/3 of the total living space. With fuel oil at $3+ per gallon there may be a reasonable payback.


g-tapes right,i say go to iso same thickness as your styrafoam(double the r value)another problem w/styrafoam is it loses the r-value over time,so i doubt the r is as high as g-tape said because its old(= crap now :wink: )