Studded Wall Insulation 

Week 5 of the One Room Challenge is all about installing studded wall insulation for our garage conversation project. 

This is also the week that delayed our entire projects by nearly 14 days. That’s a whole lot of time, especially when the entire project timeline is 8 weeks!

Our project became delayed once we realized the only option for our ceiling was spray foam insulation. We quickly found that it was cheaper and easier to hire out the spray foam ceiling insulation, rather than DIY the project. Companies were about 2 weeks out, hence the delay for the entire project.

For this post, I will discuss our studded wall insulation and walk you through the process of how to install fiberglass insulation in your walls. 

Studded Wall Insulation

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How to Determine R-Value When Insulating Stud Walls

For the most accurate R-value required for your project, the building department in your county will likely have the answer. 

Our specific R-value requirements came with the permit that we pulled, so we knew exactly what we needed. 

R-values are determined by where you live and sometimes by your specific county/city rules.  General R-value zoning charts can be found by searching online. 

We are located in Zone 5, which means the exterior walls require R13 and the ceiling requires R38.  We do not have an attic space, so we did not need to worry about attic insulation. 

How do You Insulate Stud Walls?

Before insulating your walls with fiberglass insulation, be sure to properly protect yourself.  

This includes covering all skin (face, feet, arms, legs, etc..), wearing a protective mask, closed toed shoes, protective eyewear and gloves. 

The installation process is fairly quick and painless and can be broken down into 6 steps.


6 Easy Steps to Studded Wall Insulation Installation 

  1. Prep Behind Electrical Boxes
  2. Cut Insulation Width
  3. Trim Insulation to fit Cavity Length
  4. Dry fit + Cut Around Electrical 
  5. Staple Insulation to Studs 
  6. Add Vapor Barrier (if required) 

1. Prep Behind Electrical Boxes

The first step is often overlooked when installing insulation. But it is helpful to the overall quality of the result. 

The space behind electrical outlets should be sealed with some kind of insulation. This includes low expanding foam, which fills the gap without applying too much force to the surrounding material. 

If using low expanding foam, be sure it does not get inside of the electrical outlet box and only use what is needed to fill the empty space.  

Another option is placing a piece of insulation board behind the outlet.  be sure to check your specific city or county rules to make sure you are in compliance with what they may require.

Studded Wall Insulation

2. Cut Insulation Width

Once your outlets are prepped, you are ready to cut your insulation pieces.

For all insulation, you want to make sure the piece fits snugly into the cavity, without stuffing it and with no visible gaps around the piece of insulation.

When cutting the width, we found it easiest to measure the cavity, then cut the insulation on the floor using a utility knife. This gave us the most accurate cut to fit the space. 

You will only need to cut the width if the stud cavity is not measured at the traditional 16” on center. 

3. Trim Insulation to fit Cavity Length

Cutting the insulation length is a bit quicker and easier.

Simply place the fitted insulation piece into the cavity, make sure it is snug, and use your utility knife to cut the bottom of the insulation to fit the length. 

4. Dry fit + Cut Around Electrical 

Be sure to cut around all electrical boxes,  without cutting too wide or too narrow of a hole. This should also be a snug fit around the electrical box.

DIY Insulation Install
Pro tip: mark the width of an electrical box on a scrap pieces of wood. Use this as your guide to know how wide to cut the electrical box opening.

Same goes for electric cables. You will want to slice the back of the insulation (not through the paper) so it “hugs” around all electric cables. 

Insulating 2x4 Walls

5. Staple Insulation to Studs 

Once the piece of insulation fits well into the cavity, staple it into the studs. You want a staple about every 8”, avoiding gaps and puckers. 

Woman Stapling Insulation

6. Add Vapor Barrier (if required)

Vapor barriers are typically required in mixed climates – meaning hot and humid with several heating months. 

Our zone does not require us to install a vapor barrier, but it’s important to note that sometimes a vapor barrier is needed. 

Be sure to check your city/county building requirements to see if a vapor barrier is required for your project. 

Vapor Barrier Insulation

What Thickness of Insulation for Stud Walls

When shopping for insulation, keep in mind that different R-values need so much space to fit properly and work effectively.

Simply look at the front of the packaging and it will tell you the measurements required for that specific insulation roll.

For example, the R-13 insulation below is meant for 2×4 walls, requires 3 1/2 inch thickness, and it is 15 in wide.

Since the actual measurement of a 2×4 is actually 3 1/2 inches deep, that will work perfectly for the thickness. 15 inches wide will fit 16 inches on center studs.

Where we ran into the issue with our ceiling is that it is made from 2×4 joists. And we needed to achieve a R-value of 38

The R-30 fiberglass insulation rolls we looked at  for our ceiling required at least 9 1/2 inch thickness.  This could not be achieved with our 2×4 ceiling joists, size it is only 3 1/2 inches deep.

We also did not have the space to lose much ceiling height as the ceiling slopes down to about six feet 10 in (from about 7 feet, 6 inches at the highest point). 

The workaround for us was to attach 2×6 joists onto the 2×4 joists.  This way, we would then have a 5 1/2 inch cavity to fill with insulation. 

We learned that 5 1/2 inches of spray foam would achieve an R-value of 37.5, which the county approved for our project.

What is the Best Insulation for Stud Walls?

If you are DIYing this project, the best insulation for stud walls is fiberglass roll insulation. This is what we used for the walls of our project.

It is simple to install and the most cost-effective insulation available.

What is the Highest R-value for 2×4 Stud Walls?

As mentioned above, fiberglass insulation rolls need a certain amount of space to achieve the R-value advertised.

Since a 2×4 stud is actually 3 1/2 inches deep, this may limit how much R-value you can achieve in a 2×4 stud wall. 

If you cannot achieve the R-value required in your 2 by 4 stud wall, there are other insulation options such as spray foam and blow-in insulation that may help.

Should I Insulate Internal Walls?

Typically, building requirements do not include insulating internal walls.

However, there are benefits to insulating interior walls. The biggest benefit being the sound barrier that insulation provides in-between rooms.

As always, check with your local building department to make sure your city or county does not have any requirements regarding insulating internal walls.

Studded Wall Insulation Conclusion 

Installing studded wall insulation is fairly straightforward and can be done with little effort and few tools.

Our entire master bedroom and two internal walls were done in a few short hours.

So long as you abide by the R-value requirements for your climate zone and follow the basic safety precautions outlined in this post, this is a project you can absolutely do yourself.

How to Install Insulation

Have a question or want to add an additional tip? Drop it in the comment section below!

Check out the other posts related to our DIY garage conversion:

Planning a Garage Conversion

Garage Demolition: The Step by Step Process 

Building a Garage Partition Wall

Wiring the New Garage Bedroom

Insulation Installation (you are here!)

Installing & Finishing the Drywall (coming soon)

Painting and Finishing Touches (coming soon)

Final Reveal! (coming soon)

Until next time,




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