Go Back   DIY Chatroom Home Improvement Forum > Home Improvement > Building & Construction

CLICK HERE AND JOIN OUR COMMUNITY TODAY...IT'S FREE!

Reply
 
Thread Tools Search this Thread Display Modes
Old 04-12-2010, 09:29 PM   #1
Member
 
Join Date: Apr 2010
Posts: 69
Rewards Points: 75
Default

Dividing or packing in insulaton batts...which would work best?


Ok, so I it have realized it is far better for me to add a layer of studs over an existing uninsulated drywall and then vapor barrier it warm side to create the proper wall for my office in the unheated garage (this is because the exisiting wall is 12' high and I am only going 8' up with the office wall.

My question:
The new layer of studs will be oriented "flat" on this wall. That is, the inner wall depth will be only 1 and a half inches rather than 3 and a half normally in a stud wall (because of the base ledge of concrete foundation on which they will sit accommodates this orientation best and will give a better seal on the drywall to cold floor edge.)

I know it is counterproductive to flatten (compact) the normal batts (which are normal 12 R fibreglass) down to the thinner wall dimension. But would I achieve a good result by getting 20 R batts and using only half the thickness? Surely this would be better than using only half the thickness of the 12 R batts, no?

Thanks for any tips.

Hossenfeffer is offline   Reply With Quote
Old 04-12-2010, 09:41 PM   #2
Member
 
Join Date: Jan 2009
Location: South of Boston, MA
Posts: 17,248
Rewards Points: 2,000
Default

Dividing or packing in insulaton batts...which would work best?


For a 1.5" space you need rigid foam for insulation
Once you compress the fiberglass into 1.5" you won't have much Rvalue

Scuba_Dave is offline   Reply With Quote
Old 04-13-2010, 06:47 AM   #3
Remodeling Contractor
 
Join Date: Dec 2008
Location: Sandy Hook, CT
Posts: 3,590
Rewards Points: 2,000
Default

Dividing or packing in insulaton batts...which would work best?


HUH? why studs? and definitely no batt insulation. It is only designed to work as intended. It cannot be compressed and only 1 1/2" would do no good at all. Just glue rigid foam on the wall then drywall and you are done.
Bob Mariani is offline   Reply With Quote
Old 04-13-2010, 08:40 AM   #4
Member
 
Join Date: Apr 2010
Posts: 69
Rewards Points: 75
Default

Dividing or packing in insulaton batts...which would work best?


That was my first choice....but it is so expensive.......$20+ per sheet
............that's over $160 for a small wall! Good thing I have just one wall of that dimension.
Hossenfeffer is offline   Reply With Quote
Old 04-13-2010, 08:42 AM   #5
Remodeling Contractor
 
Join Date: Dec 2008
Location: Sandy Hook, CT
Posts: 3,590
Rewards Points: 2,000
Default

Dividing or packing in insulaton batts...which would work best?


Why do anything until you can do what will work? Do you think it will be cheaper to do something that offers no gain or that may need to be replaced in a few years?
Bob Mariani is offline   Reply With Quote
Old 04-13-2010, 08:52 AM   #6
Member
 
Join Date: Jan 2009
Location: South of Boston, MA
Posts: 17,248
Rewards Points: 2,000
Default

Dividing or packing in insulaton batts...which would work best?


Pay now for the proper insulation
Or pay more long term in higher heating & AC
Plus probably putting up with a cool draft from a poorly insulated wall
Sometimes you just have to bite the bullet & buy the rigid
...or frame out a normal 2x4 wall & use reg insulation

Figure out which will work better & go from there
Scuba_Dave is offline   Reply With Quote
Old 04-13-2010, 10:20 AM   #7
Member
 
Join Date: Apr 2010
Posts: 69
Rewards Points: 75
Default

Dividing or packing in insulaton batts...which would work best?


All I posted was a question to confirm my belief that packing batt insulation was not good....and if "halving" a double R value insulation batt would result in the same as a full thickness R12 insulation.

I never did get an answer to that.....just a lashing about starting a job without wanting to pay for the proper procedure. I never suggested that.

But if I was determined to bull ahead with a stupid idea I would not have begun asking questions in the forum.
Hossenfeffer is offline   Reply With Quote
Old 04-13-2010, 11:01 AM   #8
Member
 
Join Date: Jan 2008
Location: Alabama
Posts: 608
Rewards Points: 500
Default

Dividing or packing in insulaton batts...which would work best?


Quote:
Originally Posted by Hossenfeffer View Post
All I posted was a question to confirm my belief that packing batt insulation was not good....and if "halving" a double R value insulation batt would result in the same as a full thickness R12 insulation.

I never did get an answer to that.....
Yes, compressing batt insulation decreases its R value.

As for "halving" R20, that's still not going to work.

R value of batt insulation is a function of it's "designed" thickness. That's why R12 is designed for 2x4 (3.5" thick) and R19 is for 2x6 (5.5" thick). So if you bought R19 and halved it, you would need a 2.75" deep cavity to get an R value of about R9. Stated another way, it's just a "bad" to stuff R12 into a 1.5" pocket as it is to stuff 1/2" R19 into a 1.5" pocket.
HooKooDooKu is offline   Reply With Quote
Old 04-13-2010, 12:06 PM   #9
Member
 
Join Date: Jan 2009
Location: South of Boston, MA
Posts: 17,248
Rewards Points: 2,000
Default

Dividing or packing in insulaton batts...which would work best?


There is fiberglass that is slightly more compressed for a higher RValue
R15 in a 3.5 wall = R4.3 per inch x 1.5" = R6.4...clac might not be 100% accurate
OK...checked a compression chart I have & R13 compressed into a 1.5" space gives you R6.6
R30C & R38C are also slightly more compact for cathedral ceilings

But in 1.5" fiberglass simply does not have enough rvalue
It needs the full stud depth for its stated Rvalue
I put R30 insulation into a 2x6 wall & ended up with R22 as a result

Cutting R20 in 1/2 would give you the equiv of R10
Putting that into a 1.5" wall would give you ~R5.2

So...you are back to rigid or spray foam
Rigid you can DIY, spray foam...not as easily

Scuba_Dave is offline   Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
handling unsafe work by an electrician wuxingming57 Electrical 1 11-14-2009 07:07 PM
Duct work in garage. flashme18 HVAC 1 11-08-2009 06:29 PM
Where are the "Carpenters" ???? wrldruler Carpentry 14 09-11-2008 07:37 AM
HVAC contractor ripoff! sekntonone HVAC 8 04-05-2008 07:15 AM
DIYers and Professionals Can Work Together. WilbUild Building & Construction 5 04-08-2007 01:43 PM




Top of Page | View New Posts

Copyright © 2003-2014 Escalate Media. All Rights Reserved.