What is the r-value of a wall section made of 2x4's, 1/2" drywall, 1/2" OSB, and 3 1/2" fiberglass insulation?
Question:This is for a construction materials class. I need to compair the r-factor of this wall to the r-factor of a 3 1/2" ridgid foam insulation wall.
Answers:
Couple of comments on previous answers...
Drywall and OSB do factor into the R value.
There is 3 1/2" fiberglass insulation rated at R-13 as well as R-11. I've used both. Check your local building supply store.
Your wall section:
1/2" drywall R-value = 0.45
1/2" OSB - using plywood value here - R-value = 0.62
3 1/2" fiberglass R-value = 11
Total R-value for wall = 12.07
For your rigid foam insulation wall:
1/2" drywall R-value = 0.45
1/2" OSB - using plywood value here - R-value = 0.62
3 1/2" rigid foam (depending on material R-value ranges from 4 to 6 per inch, so let's use 5 per inch) R-value = 17.5
Total R-value for wall = 18.57
In both cases you can also add R-values of 0.68 and 0.17 for interior and exterior air film, respectively.
To see if this is a worthwhile improvement you need to consider all the heat loss in the house, not just conduction through the walls. If you do this you will usually find that windows and infiltration are the major sources of heat loss and that your money would be better spent in replacing old windows with energy efficient ones and sealing up as many air leaks in the house as you can.
Here is a good link for insulation and energy savings:
http://www.coloradoenergy.org
The insulation alone is between 11-13. the sheathing and drywall might give you one more but is not rated.
The r-value is based on the insulation. Drywall and OSB do not factor in the R rating. The R-value can be found on the packaging of the insulation, and there are more than one type. The only way that I know of that you can change the actual R value is by using a vapor barrier.
Total R-value of the wall you described is about 15.
3 1/2 fiberglass has an R value of 13
3 1/2 fiberglass insulation has an R value of 11, not 13.
R-11
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