6" insulation in a 4" stud??

[bmxdukie]

Hey folks.
I have a friend that has left over pink insulation (fiberglass pink). It is 6" thick.
Enough to do the complete ceiling in my garage.
I have 2x4 studs with plywood on the top for storage in the loft.
Could I use 6" in a 4" cavity without problems?
Then drywall the ceiling.
I just want to heat the garage part time not live in it.
Thanks in advance.

 

[Robert Hall]

What do you have above the rafters?

If you have just attic space you would be fine.

If you have something else, you would pop the screws holding your sheetrock up on the ceiling.

 

[bmxdukie]

That is what I thought..I have plywood and store stuff above the rafters..
Maybe I could split it in half?

 

[Robert Hall]

Might be a bit messy, but if it's free, why not?

Wear a mask.

 

[p_mori7]

Compressing pink batt insulation WILL NOT pop the drywall scews. You will just get the same insulation value as 4".

You could also shim the bottom of your 2x4.

 

[DekeT]

Hey folks.
Could I use 6" in a 4" cavity without problems?

Short answer is yes. You will get slightly more total R value using the 6 inch batt stuffed in the 4 inch volume. Not as much as 6 inch batt in a 6 inch space though.

This topic has been the subject of previous firestorms on this board.

 

[rburke65]

I don't think compressing 6" into 4" will be popping screws.......just my opinion.....

 

[pattenp]

Owens Corning fiberglass insulation compressed R values chart.....

http://numsum.com/spreadsheet/show/21111

 

[Bucky Badger]

Short answer is yes. You will get slightly more total R value using the 6 inch batt stuffed in the 4 inch volume. Not as much as 6 inch batt in a 6 inch space though.

This topic has been the subject of previous firestorms on this board.

x2 on this

 

[xyster101]

I would say toss some 2x2 material up there and use the full 6" if you do heat the space.
I don't think it will pop drywall screws if you don't shim. Just use liquid nails and do screws 8" apart in the field of the drywall.

 

[bmxdukie]

Thanks guys.
Sorry if this has been covered before. Just getting used to this site.
I think I will shim the studs and go from there.
Thanks!

 

[Moose97]

I think shimming the studs is a good idea. Gets you a full R-19 value but as the posted chart says, it won't be worse than R-13. If its just a part time shop you may not mind that.

 

[mp23]

I did the exact same thing in my garage and interior house walls, no problems at all.

 

[NUTTSGT]

I'd shim the studs if you can. If not, compress the insulation to make it fit. I wouldn't buy insulation to compress it but free is free. Even better is this "free" will save you serious money in the long term.

 

[rsanter]

Yes you can but the insulation value will be reduced
For fiberglass insulation to work you must have the correct fluf.
What you can do is peel some if it away to thin it out so it will become 4" insulation
The more you compress the insulation the more of a conductor it becomes

Bob

 

[ADSR]

You will get slightly more total R value using the 6 inch batt stuffed in the 4 inch volume.

I disagree with this. I've been building a long time and this subject has come up a million times. I've been told by many pro insulators, that if you compress batt insulation, you reduce the R-value. The compressed mass can now transfer cold right through the wall as a solid object. It works just like cold joint transfer does, but not a 2x4/6 stud. You're dealing with a 16/24" cold joint.

 

[ADSR]

Yes you can but the insulation value will be reduced
For fiberglass insulation to work you must have the correct fluf.
What you can do is peel some if it away to thin it out so it will become 4" insulation
The more you compress the insulation the more of a conductor it becomes

Bob

Beat me to it.

 

[87jeepwrangler]

2x4 ceiling joists do a pretty aweful job of holding weight. You will more than likely overload your attic with stuff and begin to see ceiling sag. The way I see it, you have a few choices.

1. Leave the existing setup, smash your free r-19 into the 2x4 bays, drywall it, and enjoy your free insulation. It will be approx. r-13 equivalent, give or take.

2. Add a spacer to increase your joist depth to near r-19 thickness and enjoy the added R value in your ceiling. A little more labor and cost up front, but the more you heat the shop, the more it will benefit you long term.

3. Sister (or replace) your 2x4 joists with larger lumber (probably 2x6). Assuming you still have open framing and can land the 2x6s appropriately, and not only get the added benefit of r-19 ceiling insulation, but also be able to store a little bit of weight up in your attic without sagging your joists. Granted you would loose a theoretically small R value from additional lumber between the heated and unheated space (heat bridging, etc), this in my opinion is your best option, but probably a little more expensive and time consuming.

Again, this info is based on a few assumptions I made from your post, based on things like joists spans, framing type, etc

Ultimately you need to make your own decisions based on how permanent, long term, and what you plan to use the shop for.

 

[DekeT]

I disagree with this. I've been building a long time and this subject has come up a million times. I've been told by many pro insulators, that if you compress batt insulation, you reduce the R-value. The compressed mass can now transfer cold right through the wall as a solid object. It works just like cold joint transfer does, but not a 2x4/6 stud. You're dealing with a 16/24" cold joint.

Yes fiberglass insulation is lowered when you compress it. Yes if you squeeze it flat you lose almost all it R value. That is not what you are doing in this case. Yes, the total available R value of a 6 inch batt is lowered if you squash a 6 inch batt into a 4 inch space. The TOTAL R value of that squashed 6 inch batt in the 4 inch space is still more than a 4 inch batt in a 4inch space.

Information provided by poster rsa:

greenbuildingadvisor.com editor Martin Holladay addressed this exact subject in a finehomebuilding.com forum thread
Quote:
Compressing a 5.5 inch batt to 3.5 inches will reduce the R-value compared to the same batt installed in a 5.5 inch cavity, but will increase the R-value per inch compared to a 3.5 inch batt installed in a 3.5 inch cavity.

In other words, fiberglass manufacturers have not optimized the density or the R-value per inch of their product. They sell a fluffier-than-optimum product in order to reduce the cost of manufacture. If you are willing to buy the 5.5 inch batt and compress it, your 3.5 inch cavity will have a higher R-value than if it were filled with a 3.5 inch thick batt.

 

[Cobra6]

Hey folks.

I have 2x4 studs with plywood on the top for storage in the loft.

So your "storage" trusses are just 2"x4"? what will you be able to store there?

 

[bmxdukie]

Cobra, the only things I store there are thinks like the pool toys, some camping equipment, ski boots and the like.
I wouldnt have over 300lbs..I also spread out the weight in the 20 x 30' span.
The highest spot I can store is the peak. It would be abour 3.5'tall and it is a standard gable.
You couldnt walk up there. Just very light storage.
I was thinking of doubling the studs on every other so maybe I should use 2x6 in those spots?