What is the best insulation for a 2×4 wall?

Insulation for 2×4 Walls

In most wall applications, you will use R-13 or R-15 kraft-faced fiberglass insulation rolls for these two-by-four stud walls. While rated differently, these two types of insulation are close enough in thickness that they can both fit into modern two-by-four wall systems.

Can you put rigid foam insulation between studs?

Rigid foam board pieces are difficult to fit snugly between studs so you would have to spray foam to fill any gaps. Unlike loose-fill or batt, foam board insulation can’t easily be cut to perfectly contour around pipes or wires.

Can you put foam board over studs?

Now as far as your plan to use XPS – high density foam – on top of the studs before the drywall should be fine. The XPS is a vapor barrier but you’d need to tape the seams or have poly in front of it. Boarding will be more of a challenge though as you can’t see the studs.

How much R-value does a 2×4 wall have?


They are available in widths suited to standard spacings of wall studs and attic or floor joists: 2×4 walls can hold R-13 or R-15 batts; 2×6 walls can have R-19 or R-21 products.

What is the R-value of 2 rigid foam?

Foam Board Insulation R-Value per inch

Thickness (in Inches) R-value (in I-P/Imperial) RSI (R-value in Metric)
1.5 9.3 1.62
2.0 12.4 2.16
2.5 15.5 2.7
3.0 18.6 3.24