When you are insulating 2x4 and 2x6 framed exterior walls and want to use fiberglass insulation, what thickness should you use?
In most applications, you will use R-13 kraft-faced fiberglass insulation rolls for 2x4 stud walls and R-19 for 2x6 walls:
|Insulation Type||Thickness of Insulation Itself||Appropriate For Wall Type:|
|R-13||3.50"||2 x 4 stud walls|
|R-15||3.50"||2 x 4 stud walls|
|R-19||6.25"||2 x 6 stud walls|
|R-21||5.50"||2 x 6 stud walls|
When Too Much Becomes Too Little
Insulation works partly by trapping air pockets within the insulation. If you cram too much insulation into a too-thin wall, you reduce the insulation's air pockets.
Thus, it is pointless or even counter-productive to put R-19 into a 2x4 wall, for example.
What to Do If Your Walls Are Too Thin
You run into problems if you live in a cold climate where your R-value needs exceed the space you have available in your wall cavity.
As noted above, R-19 insulation only works when it is an appropriately sized wall; that is, one that allows the insulation to expand enough to create air pockets that trap warm air.
Because you cannot rebuild your walls with 2x6 studs, you need to look in other directions:
- Add thick insulation batts to the attic.
- Seal up door and window cracks with caulk.
- If you plan to re-side your house, add exterior wall sheathing beneath the new siding. Sheathing can help boost your walls as much as an extra R-6.