# r-21 vs r-19 insulation



## gamebird (Feb 5, 2017)

I'm wondering if anyone has used the r-21 insulation as opposed to standard r-19. Is the difference between the two make up for the price difference?


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## Windows on Wash (Aug 30, 2011)

Probably the difference between low density and high density. 

The higher density stuff is better does resist the convective looping issues that lower density FG batts suffer from.


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## Bud9051 (Nov 11, 2015)

Hi gamebird and welcome to the forum.
Mathematically there is a difference as I can run the energy cost calculations with both numbers and say, it will save you X dollars by using the r-21. But you will never feel the difference, only your check book will be able to tell the difference and that will not be a big number. 

Example, my climate (Maine) and my fuel cost $2.25/gal of oil.
1,500 ft² of exterior wall surface insulated to either R-19 or R-21.
Annual energy cost for R-19 = $255
Annual energy cost for R-21 = $229
Theoretical savings, $26 per year and that is overstating those savings because the wall assembly is only 80% cavity insulation and the rest is thermal bridging. So call it $20 per year, sure wouldn't justify a lot of added expense.

But, I would definitely go with detailed air sealing and the R-21. In fact, newer codes may mandate it.

As an FYI, document all improvements as future regulations will want to have every home tested for energy performance and make those results part of the evaluation. So you will not only save a few bucks every year there may be a return when you sell. Plus, when you add up many improvements they all count.

Bud


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## Gary in WA (Mar 11, 2009)

--------------Welcome to the forums!--------------------------

R-21 has *19% *more R-value than R-19 in your 5-1/2" wall cavity; http://www2.owenscorning.com/litera...nsity (for 2x6 Exterior Walls) Data Sheet.pdf

Because it is High Density, it will stop convective loops that occur in R-19 (low density) insulation (as said), the new "biggest loser"; http://www.diychatroom.com/f98/biggest-loser-fiberglass-insulation-90438/

Even if you do an excellent job of air sealing; caulking all joints at sheathing/studs/plates, -- and ADA the drywall,you could get convective loops due to large temperature differences between interior/exterior, if in a cold climate. This in turn could deposit moisture (room diffusion) at the top of your sheathing, especially with any gap where the vapor retarder paper is not in full contact with the back of drywall (inset stapling, etc.). Replacing that could get expensive, esp. if one had brick veneer...

Gary


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