1 Simple Reason Why R-19 Is Not So Effective In A 2X4 Wall!

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Is It OK to Put R-19 in a 2×4 Wall?

Are you planning to build a new garage? Will you be framing the garage walls using 2X4 studs? Quite possibly, since use of 2X4 is pretty common for garage wall framing. 2X4 walls are just fine for R-13 or R-15 insulation. But is it OK to put R-19 in a 2X4 wall? ,

R-19 insulation crammed in a 2X4 wall will result in effective insulation of less than R-15.

The small air pockets trapped in the insulation fibers, not the fibers themselves, are responsible for the insulation. Compressing them in a smaller place reduces its effectiveness.

Insulation material, batts or rolls are placed in the stud cavity in the garage wall. The stud cavity is the empty space between two adjacent vertical studs, the bottom (aka sole) plate and the top plate.

The actual dimensions of a 2X4 stud is 1 ½” X 3 ½”. It is standard practice that vertical wood studs are spaced 16” on center (OC). The result is that the stud cavity is, in fact, 14 ½” wide and 3 ½” deep.

Brands manufacture insulation batts & rolls to fit snugly into the stud cavity. The batts & rolls are not designed for being compressed. Compression will reduce their effective R-Value.

NOTE: Rockwool and Owens Corning are the two most well known brands in the insulation industry. Their product quality & features are comparable.

What is the Highest R-Value for 2X4 Walls?

The R-Value for a 2X4 wall ranges from R-11 to R-15. The insulation batts & rolls in this range are 15″ wide and 3 ½” thick. They fit snugly into the 2X4 wall stud cavity.

For example the dimensions of Owens Corning R 15 Fiberglass Batt Insulation Fits 2X4 Exterior Walls are R-15 type, 15W x 93L x 3.5 in. thick. The packaging clearly states it is for 2X4 walls.

How Much Insulation Can You Put in a 2×6 Wall?

The R-Value for a 2X6 wall ranges from R-19 to R-23. The insulation batts & rolls in this range are 15″ wide and 5 ½” thick. They fit snugly into the 2X6 wall stud cavity.

The dimensions of Owens Corning R-19 Fiberglass Batt Insulation Fits 2×6 Floor or Walls are R-19 type, 15W x 93L x 6.25 in. thick. The packaging clearly states it is for 2X6 walls.

If you compress it to fit into a 2X4 wall, you are reducing the thickness from 6 ¼” to 3 ½”. A lot of the air will be squeezed out of the air pockets. The R-19 insulation batt will end up being less effective than even R-15 insulation.

The thickness of R-19 insulation batt is 6.25 in., which will work fine with old houses where a 2X6 stud was actually 2″ X 6″. This will be a bit too thick for a modern 2X6 stud wall as the actual stud dimensions are 1 ½” X 5 ½”.

You will be better off opting for Owens Corning R-21 Fiberglass Batt Insulation Fits 2×6 Floor or Walls. The dimensions are R-21 type, 15W x 93L x 5.5 in. thick. The packaging states that it is suitable for 2X6 walls.

The conclusion is clear. You can not exceed R-15 in a standard 2X4 wall using insulation batts or rolls. An excerpt from Owens Corning datasheet

R-Value	Batt Thickness	Suitable For
11	3 ½”	2X4 Wall Framing
13	3 ½”	2X4 Wall Framing
15	3 ½”	2X4 Wall Framing

20	5 ½”	2X6 Wall Framing
21	5 ½”	2X6 Wall Framing
23	5 ½”	2X6 Wall Framing

What Is the R-Value of Closed-Cell Spray Foam in a 2×4 Wall?

What can you do if you want a R-Value higher than R-15 in a 2X4 wall? You will need to use Spray Polyurethane Foam (SPF) instead of Fiberglass Batt or Roll insulation.

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SPF insulation comes in two parts – an iso and a resin in two separate tanks. The two liquids are sprayed together through a spray gun. The two liquids react with each other to form a foam which can be 40X to 100X of original volume.

SPF is very effective as it insulates and air seals wherever it is applied.

Open Cell SPF results in a Low R-Value (3.5 – 3.6 per inch). The maximum R-Value of only R-12.6 can be reached in a 2X4 wall.

Closed Cell SPF results in a High R-Value (4.9 – 7.1 per inch). R-Value of as high as R-24.85 can be reached in a 2X4 wall.

Below is the comparison between Open & Closed Cell SPF.

What Insulation Is Better Than R19?

R-Value is a measure of the “resistance to heat flow”. The higher the R-Value, greater is the “resistance to heat flow”. A material, a door, a wall with higher R-Value is simply better insulation.

R-15 insulation batt will insulate better than R-11 and R-19 insulation batt will insulate better than R-15.

So, what is better than R-19 insulation batt? R-21 or R-23 insulation batt will insulate better than R-19.

R-19, R-21 and R-23 insulation batts are 5 ½” thick and need to be installed in 2X6 stud walls.

However, you do not always need a higher R-Value. The required R-Value really depends on the climate zone of your home’s location. Check it out in the map below from IECC: