The Spruce / Madelyn Goodnight
Thetype of insulationand its thickness are the most critical factors when insulating exterior walls.
Adding too little or too much insulation means wasted energy.
Learn the best insulation for exterior walls, whether 2x4 or 2x6 wall systems.
The Spruce / Madelyn Goodnight
Insulation to Use
For 2x4 walls, use R-13 or R-15 insulation.
For 2x6 walls, use R-19 or R-21 insulation.
With either key in of wall, use kraft-faced fiberglass or mineral wool insulation.
The Spruce / Jason Donnelly
Drill in another area and give it another spin.
Wall assemblies, especially those in older homes, are built with two-by-four (2x4) studs.
The wall thickness will be 3-1/2 inches, not 4 inches.
The Spruce / Jason Donnelly
The width of modern 2x4s is 3-1/2 inches.
Older homes may use two-by-fours with a true measurement of 2 inches by 4 inches.
In this case, use R-13 or R-15 fiberglass or mineral wool insulation.
A thick down-filled jacket or sleeping bag works the same way.
When the feathers fluff up and create air pockets, thermal resistance is at its greatest.
Other Ways to Insulate
Insulating the exterior walls is just a start.
Climate, bang out of home, and wall location determine whether exterior walls need vapor barriers.
The most affordable way to insulate 2x4 exterior walls is with R-13 kraft-faced roll fiberglass insulation.
This insulation costs $0.60 to $0.70 per square foot.
U.S. Department of Energy.
