2x8 Ceiling Insulation

2×8 Ceiling Insulation [4 Variety Explained]

It’s very frustrating when your ceiling is just burning up. And you don’t have a clue about what insulation you should use. 

So, What would be best for 2×8 ceiling insulation? 

Well, a 2×8 ceiling insulation needs a 7 ¼ ” depth clearance. To cover that up the best choice can be an R-25 insulation, which has 7 ½ ” depth. But considering facts you can also use R-30 insulation for your 2×8 joists. For cost-cutting, your R-19 or R-21 insulation can also be a great choice. 

You must still be pretty confused about that matter. Don’t worry this whole article is prepared just to clear your head out. Let’s jump to the detailed discussion. 

2×8 Ceiling Insulation – 4 Variety Explained

If you do have the room, more shielding is typically preferable. The cost-benefit of adding more shielding will be determined by how you use the storage. 

I would suppose that the walls have already been or will be sealed.

You’ll probably be just fine. However, excessive compression can lower the insulation’s R-value. With fiberglass, at least. I assume it’s okay if you keep it jutting out. 

So how are you securing it in between the joists? Do you have a rationale for using 2×8? Are you simply looking to save money since you already have some?

2×8 “If the 2×8″ batts are not crushed, batts offer better insulating than 2× 6” batts. I thus would choose 2×8 “joists and actually abandon the insulation stick there. The dilemma is kind of like a 2×4 or 2×6 wall shed. 

Unless the joists are insulated in some way along their top edge. You will lose heat through any sort of insulation you use.

Here’s a  table for insulation R value when compressed in a framing cavity is provided here.






Insulation R-Value When Compressed In Farming Cavity 
I Joists 

I Joists 




11 ¼ ” 




I Joists 



9 ½ ” 

9 ¼ ” 

7 ¼ ” 






35 29 3025  27  24




5 ½ “












2116 2016 1814




3 ½”

2 ½”  












The change in R-value from packing insulation made for 2×8 into a cavity made for 2×6 will be minimal.

For 2×6 cavities, R-21 insulating is available. Although R-30C will only compress to R-22 value if purchased.

Fiberglass and air space must be carefully balanced to create insulation. Heat does not transmit well through the air. The ideal R-values for your 2×8 roof insulation are discussed here.

Option 01: Applying R19 

The 26 roof insulation is the major use for R 19 insulate. However, you may easily utilize it as insulation for your 2×8 ceiling. When it is placed on 2×8 walls, you can compact it. 

In fact, the package’s tiny print suggests a lower R-value for 2×6 construction. However, larger R-values equate to significantly greater insulation.

Consequently, if the heat is intolerable and your roof is closed. Therefore, it would be better to avoid using an R-19 for your 2×8 ceiling insulation. Even so, there will be an air bubble to keep the heat out.

But there’s another thing to think about. if your finances are tight. Then you might think about installing R-19 in your ceilings.

R-19 might be another option to think about for your carport ceiling. if you don’t use your garage very often. And here is another choice that will save you money and be more successful.

Option 02: Applying R-25 

The ideal protection for a 2×8 roof is R-25. A 28 roof measures 7 14 in “confined height The R-25 shielding can conceal that completely.

Some companies produce an R-25, but I believe it needs 7 12 “to be cleared. I would conduct an online search for what is offered at a few of the nearby large box stores.

Here are a few R-25 soundproofing options for you to consider.

Product 01
Product 02

this R-25 insulation is custom-made. And they will be a great help for you. 

The quality of these insulations is quite good. And your 2×8 roof joists will be ideally placed alongside them.

Option 03: Applying R-30 

You can get roughly R25 in your 2x8s using compression R30. at the age of 16 “It makes sense that tapes of R30 are so cheap. For whatever reason, those bats cost $2 more for each sq foot ($.87 vs. $.38).

You might add a layer of one for $.32 per square foot “On top of the rafters. Place R4 EPS insulation to lessen heat transfer.

We might think about installing vents. Additionally. It supports the adage that better insulation has a higher R-value.

But some people come to the conclusion that fiberglass is compressed. Some air gaps inside the window will be reduced. You might also keep in mind the possibility of some R-value reduction.

Whatever the R-value you choose. It is always a dilemma like choosing 4×4 or 6×6 for pole bam. But you should consider one according to your needs.


How should I insulate my ceiling?

You will require a varied R-Value based on where you reside and the area of your house you are insulation (walls, basement, attic, etc.). R-13 through R-23 is typically recommended for external walls, whereas R-30, R-38, and R-49 are frequently used for roofs and attic areas.

Is insulation capable of being thicker than joists?

Foam that is deeper than the height of the roof deck should have 2 layers for the best effects. The initial layer’s strip thickness ought to be greater than or equal to the joists’ width.

Does the insulation in ceilings require a vapor barrier?

Vapor barriers are necessary in most environments. For that purpose, some architects use batts with an affixed kraft paper facing, while Tom suggests using unfaced batteries that are wrapped in plastic and have all of their seams sealed.

Bottom Line 

Thanks a lot for tagging along till the very end. Hope now you are sure about 2×8 ceiling insulation. 

If you find any problem regarding that issue after that. It’s best for you to console a professional. 

Best of luck.

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