Go Back   DIY Chatroom Home Improvement Forum > Home Improvement > Insulation

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

Reply
 
Thread Tools Search this Thread Display Modes
Old 02-18-2014, 02:30 AM   #1
Newbie
 
Join Date: Feb 2014
Posts: 8
Rewards Points: 10
Default

Ideal R-Value for basement wall before it becomes overkill


I've already started with 2" xps on the poured foundation wall. I currently plan to framed it out with 2x6 16 "o.c. about 1" away from xps and fill in studs with roxul . My question is, how much of an r-value is good enough before it becomes overkill and a waste of money? I planned on using roxul and there are 3 types available in my area:

r15 $38 60sq' (r25 w/xps)
r23 $43 40sq' (r33 w/xps)
r30 $47 30Sq' (r40 w/xps)

My region is northern midwest Chicago area. Climate all winter has been well below -0 for the most part. It will be a finished basement for recreational use. heating will most likely be gas furnace.

jim20j is offline   Reply With Quote
Old 02-18-2014, 06:47 AM   #2
MarginallyQualified
 
Join Date: Dec 2011
Location: Winston-Salem NC
Posts: 3,682
Rewards Points: 2,038
Default

Ideal R-Value for basement wall before it becomes overkill


Quote:
Originally Posted by jim20j View Post
My region is northern midwest Chicago area.
...how much of an r-value is good enough...?
No such thing as "overkill" if they'll keep taking your Visa card

Quote:
I've already started with 2" xps...
plan to frame it out with 2x6 ... and fill in studs with roxul.
The 2x6 and that extra inch between is probably at the overkill end of things.

Otherwise, having the framing right up against the XPS works better on several levels. The roxul ratings are based on their depth (eg: 3.5" @16"C/L = R14).

hth


Last edited by TarheelTerp; 02-18-2014 at 06:50 AM.
TarheelTerp is offline   Reply With Quote
The Following 2 Users Say Thank You to TarheelTerp For This Useful Post:
jim20j (02-18-2014), Windows on Wash (02-18-2014)
Old 02-18-2014, 04:59 PM   #3
Exterior Construction
 
Windows on Wash's Avatar
 
Join Date: Aug 2011
Location: Washington DC Metro Area (VA, MD, DC)
Posts: 6,704
Rewards Points: 2,682
Default

Ideal R-Value for basement wall before it becomes overkill


+1

Probably could have run the framing tight to the foam but at this point you probably want to fill the entire cavity (i.e. don't leave an air space).
Windows on Wash is offline   Reply With Quote
Old 02-18-2014, 05:20 PM   #4
Member
 
concretemasonry's Avatar
 
Join Date: Oct 2006
Location: Minneapolis/St. Paul, Minnesota - Latitude 45.057 Longitude -93.074
Posts: 3,800
Rewards Points: 2,088
Default

Ideal R-Value for basement wall before it becomes overkill


Just keep in mind that for a basement the soil behind the walls is far warmer than the outdoor AIR temperatures in the winter. As an extreme, here (MN) it can be -20F for days (air temp without winds) and the soil is about 50-55F about 4' down, so a basement does not see the same conditions. There is the lateral conductive heat flow that is quite slow. The soil temperatures in the soil can reduce AC costs in the summer for conditioned spaces if they are below grade. - That is common here.. Keep in mind that a basement has more square footage exposed to Mother Nature than to the air above grade. Just get rid of the obvious drafts in the livable space.

Basement are different than above grade because lightweight frame construction has little(if any thermal mass storage). - It seems ironic that people build large frame homes and then use geothermal for heating and cooling.

Too bad the "scientists"/"specialists" that study the decimal points and details in R-values for individual materials do not address the same effort when it comes to a whole structure instead of micro-managing small air flow paths that have little effect on a daily basis. If I had a frame home on a basement, I would spend my time in a basement, close the doors to the upstairs if the power was out for an extended period and then drain it and let it freeze.

The details are much more fun to talk about and speculate on.

Dick
concretemasonry is offline   Reply With Quote
The Following User Says Thank You to concretemasonry For This Useful Post:
jim20j (02-18-2014)
Old 02-18-2014, 11:55 PM   #5
Newbie
 
Join Date: Feb 2014
Posts: 8
Rewards Points: 10
Default

Ideal R-Value for basement wall before it becomes overkill


Thanks for your replies.
My reasoning for 2x6 is that the R23 is 5 1/2". The 1" gap is because 1/4 of my foundation wall has a 6" waste line running across it, so to clear it, I would need 7" off the wall. Now that I think about it, I forgot to factor in the 2" of xps, so I need 5" off the wall. Even with 2x4 frame, I would still need an additional 1 1/2" to clear the waste line. The 1" gap is for the framing alone,the roxul will be pushed against the foam.

So, for the waste line wall, if I go 2x4 framing against xps and leave a 1 1/2" gap to make 7" but push roxul to the foam and fill up the rest of the 1 1/2" with split layers or somehow, I believe that would suffice?

According to my calculations assuming they are correct, R30 roxul would be $562 more than R23 for the entire basement, so I will go the r23 route.

Thanks again!
jim20j is offline   Reply With Quote
Old 02-19-2014, 12:41 AM   #6
Member
 
Join Date: Jan 2012
Location: Pittsburgh, Pennsylvania
Posts: 174
Rewards Points: 150
Default

Ideal R-Value for basement wall before it becomes overkill


Just curious. What is the reason for the Roxul as opposed to fiberglass or even spray foam?

I am not sure but for the cost of the Roxul, you might be able to get a DIY spray foam.

Also, do you ne to frame all of teh walls out or just one with the waste pipe?
bcgfdc3 is offline   Reply With Quote
Old 02-19-2014, 05:19 AM   #7
Newbie
 
Join Date: Feb 2014
Posts: 8
Rewards Points: 10
Default

Ideal R-Value for basement wall before it becomes overkill


I currently do not have any moisture issues, however I also do not wish to have any in the future. I plan to be here a long time and it's more of a peace of mind knowing if excessive moisture were to occur. And from what I have read so far, it also serves as a fireblock. Sprayfoam seems to be an over budget route. it's not totally out of the question. I intend to frame out and finish the entire basement. 1500sq ft
jim20j is offline   Reply With Quote
Old 02-19-2014, 10:34 PM   #8
Registered User
 
Join Date: Mar 2009
Posts: 9,968
Rewards Points: 2,000
Default

Ideal R-Value for basement wall before it becomes overkill


Overkill is adding any cavity insulation to the foam board. With an empty cavity, the inside face of the FB would be at about 58*F and safe to 73%RH, the HVAC in basement (68*F) would take care of any moisture. The more cavity fill insulation in front of the FB, the colder it will be/lower the dew-point temp, Fig. 3a- without cavity fill------ Figs.4a,4b each with additional insulation; http://www.buildingscience.com/docum...nsulation/view

R-15 +R-10= 45*F inside face with dew-point there at 43% Relative Humidity in basement at 68*F. For Chicago- 3 lowest months averages; http://www.weather.com/weather/wxcli...graph/USIL0225

R-23 +10= 41*F FB w. 38%RH---------- R-47 + R-10= 36*F FB temp and safe to only 30% RH basement air till condensation.

Gary
PS. Some AHJ's require fire-blocking every 10' (per code) between the FB panels, check locally.
__________________
If any ads are present in my answer above, I do not condone/support/use the product or services listed, they are there against my permission.
Gary in WA is offline   Reply With Quote
The Following User Says Thank You to Gary in WA For This Useful Post:
Windows on Wash (02-20-2014)
Old 03-07-2014, 10:49 PM   #9
Member
 
Join Date: Nov 2009
Location: west of chicago
Posts: 395
Rewards Points: 274
Default

Ideal R-Value for basement wall before it becomes overkill


I'm late to this thread but I'd like to ad, in this area ( I'm an 1hr + 1/2 west of Chic. )
you should consider having a dehumidifier in your basement for the times of the year when you need it.
Winter I'm putting in humidity through the hvac ( April air) , summer the Ac takes care of it , but Spring rains ( high indoor relative humidity)with still cold frozen ground could spell trouble condensation wise ( in your basement walls).

I went with 1"xps with R11 stud batts and the basement never got below 63f with heat vent barely open . Canned lights ( there's plenty and they actually help to heat) and vents all open ..64-65-66f in no time.
Ceramic tile floor hurts me for better temps but I'm comfy.

High Gear is offline   Reply With Quote
The Following User Says Thank You to High Gear For This Useful Post:
jim20j (03-08-2014)
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
Retaining wall work-- what approach? emcelvaney Landscaping & Lawn Care 2 09-24-2012 07:49 PM
How to face a cinder block retaining wall with stone? CarrollY Concrete, Stone & Masonry 5 09-04-2012 12:26 PM
Adding wall with door opening - sloped ceiling and no joist for top plate Jebross Remodeling 11 01-11-2012 09:34 AM
Retaining wall problem FMS Landscaping & Lawn Care 6 07-04-2011 06:42 PM
Atlantic-need your opinion on markd's comments about my vapor barrier? yummy mummy Building & Construction 11 03-07-2007 09:47 AM




Top of Page | View New Posts

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