Adding studs to ease installation of insulation?

So, I have an older A-Frame that I am trying to upgrade and part of the process includes replacing the insulation in exterior walls. One of the problems that I have is that the studs are unevenly spaced but they generally trend between 20 - 22.5 inches. I am having a hard time finding 23" wide insulation for 2x4 walls unless I want to drop a lot more money then I need to fill the insulation in the wall space available. I have thought of two options to avoid said expense:

1. Buy 15" wide insulation which is plentiful and install them next to each other. I understand that this is not ideal given the risk that it might create a void that would not otherwise be there, but is it really an insulation killer?

2. Given that the rooms are not really big, would it be nuts to add faux-studs in between the existing studs to make the width for insulation less, thus making it easier to use the 15" width insulation? As noted, as an A frame most of the external walls are not super tall so it would not take a ton of 2x4's to do the trick (particularly in the main room where most of the problems are, which is cathedral style). Setting aside the time to do this, which would be minimal given that I am doing it over the next few months, are there notable problems with such an approach?

Thanks for any thoughts

PS. I understand that the best option is to pay the extra money, get the proper fitting insulation, and install it. I am just looking for feedback on options 1 and 2.

 

I find it hard to believe you can't find R13 for 24" centers. But it could be due to yet another Covid shortage. This is what's in stock locally, and is an example of what you should use. With the price of lumber it would be asinine to add studs and/or have to cut 15" insulation to fit. You would have more waste than you can imagine. So I dont quite get where you think the savings is coming from.

What's in the link would be ready to staple up, no cutting other than cross cuts for lengths.

There is no question what you should do... find the insulation in the link above. And I don't see how you think it is "extra money" to get something that fits exactly... and you would only need to cut down if the bays are more narrow than 22.5.

 

If your adding studs then the walls must be open, have foam or cellulose installed and now you have the best.

 

I get the point that fitting the insulation to the existing studs is the preferable approach. Just trying to explore other alternatives, none of which might work well. As far as I can find, all of the 2x4 23 inch wide insulation is back ordered to mid-late August in Western VA, where the work is being done. Not available in the DC area either, where I live. In the meantime all orders for that time frame require "bulk" which would give me much more than I need for the wall space.

Correct me if I am wrong, but adding foam or cellulose is not diy, right? The place needs some work, and money will be spent on new doors and windows and etc., but I am trying to do as much as possible myself.

 

Ok, I appreciate the feedback. Looks like some might be currently available at a not too dreadfully far away Home Depot. But, am still curious about the foam and or cellulose option. Not diy assuming?

 

A DIY option is to use solid foam insulation board. It may cost more but you get higher R values for the same thickness. You could use 2 inch sheathing foam board for R-13 or standard for R-10. Or you could fill the 3.5 inch cavity with 2 inch and 1.5 inch (stagger any seams) for a total of R-21.75 or R-17.5. (Fiberglas 3.5 inches is R-15.)

Foam board comes in 4 X 8 foot sheets so you can cut to the needed widths. (Some also come in 2 X 8 foot size.)