How much is too much insulation?

[ShellbackBill]

SO, let's say the recommended R value for my walls is 14.

What's the downside to making it 20 or 28?

Seems that would just mean lower utility bills.

And if I feel like cranking the thermostat up to 75 in the winter, I'd still use less energy than a normally insulated house at 72.

 

[Snoonyb]

The value of the insulation is the encapsulated air, so when you compress the insulation you reduce it's ability to contain air, thereby defeating the purpose.

 

[Steve123]

There is no "too much". Just a cost vs payback question.

If you have 2 x 6 studs, you can fit R16-R-17 of fiberglass batts in there. If you want R28, you need XPS or closed cell spray foam --- quite a bit more expensive.

 

[oldognewtrick]

Where you encounter problems is when you create a double vapor barrier and moisture is trapped in the insulation. Weather sealing is just as important as insulation.

 

[ShellbackBill]

Thanks!

Looking at 2x4 with fiberglass, then 1 or 2 inches foam board, then sheathing.

I think that would give me 21R

 

[WindowsonWashington]

If you are looking at rigid board, the foam should, ideally, be to the outside of the home and would serve to help thermally uncouple the framing from the home. Where is the home located?

 

[ShellbackBill]

It's located in SouthEast Texas, about 60 miles east of Houston.

I'm nearing retirement. My monthly income will obviously be reduced soon.

I expect to live the remainder of my life in this house, hoping for 30 years or so.

Low utility bills during those years would be welcome. I am putting on a version of the Texas Cool roof, as the house needs a new roof anyway.

Google "The Texas Smart Roof The Coolest Roof in Texas", there are pictures there. A local roof contractor does something similar, but not similar enough to be a copyright violation. (I hope. )

Our main energy cost down here is air conditioning.

 

[Brian Famous]

Adding the rigid board would absolutely provide a benefit to help better insulate the home if applied to the outside.
I'm assuming this means you'll also be doing new siding of some sort since I can't imagine how you would add rigid board on the outside without doing new siding... Keep in mind that adding even 1" of rigid board is also going to change the depth of sills needed for all of your windows, as well as reducing the depth of overhang of eaves, etc...
All of that extra effort and expense may cost more than your projected savings over time.