how much difference in price and quality between R19 and R20 per square feet ??0 y/ {& w: b& Q5 p/ h$ ]. a9 b( u
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who can explain why use R30 for attic. + \+ ]- k3 s" }- F! L
1#KochFord " N0 y9 O: T, i# Q$ X: Y) x/ tThe higher R value, The better insulation performance.5 e# _* f5 u6 s
In winter, the hot air always floats up due to thermal buoyancy, so R value for the roof is normally higher than that for exterior wall.5 w. d" L, r* U) }; M. a* Y7 C8 v2 S- _
Hope my answer helps.