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 01-29-2014, 02:12 AM   #1
Newbie
 
Join Date: Jan 2014
Posts: 6
Share |
Default

Another Cantilever Insulation Question


Hi guys. I was just looking for advice to see if I'm on the right track. I want to drywall the ceiling in my basement but before doing so I want to properly insulate and seal the cantilever cavity of the floor above. The cant. is approx 2 feet deep. I realize that there are many ways to skin this cat, some better than others. My limitations are that it's winter right now and I can't do anything from the outside (ie remove the plywood attached to the bottom of the joists outside) therefore I want to do this job all from the inside. I would however consider finishing this from the outside this spring if I have to. My goal is to do what I have to do before putting up my drywall ceiling.
I want to use 2 in. xps, caulking and expanding foam. Not sure if batting or Roxul is required to fill in space.

At the moment, looking into the cant. between the joists while standing on a ladder in my basement, my plan is to seal the rim joist with caulk. I would then adhere 2 in. xps to the top of the cavity against the subfloor above and seal it all around with expanding foam. I would then seal the mudplate and the joint where the outside plywood meets the foundation wall with caulk. I would then block the cant. between the joist at the top of the foundation wall with 2 in. xps and seal it with expanding foam.

Will this be an effective way of accomplishing insulation and sealing. Am I missing a fundamental principle of insulating and sealing cantilever floors.

Should I instead put the xps against the rim joist and bottom of the joists, laying on top of the outside plywood but on the warm side of the house.

Is placing FB in the empty cavity beneficial (whether the xps is on top or on the bottom)?

My floor upstairs has never been cold, but I imagine that's due to the warm air from the basement heating it. Once the ceiling is drywalled, that will be a different story.

I have attached a couple of pictures. At the moment, my plan is the second picture. Any advice would be greatly appreciated.

Yanick
Attached Thumbnails
Another Cantilever Insulation Question-slide1.jpg   Another Cantilever Insulation Question-slide2.jpg   Another Cantilever Insulation Question-slide3.jpg  

crank73 is offline   Reply With Quote
Old 01-29-2014, 06:14 AM   #2
Exterior Construction
 
Windows on Wash's Avatar
 
Join Date: Aug 2011
Location: VA, MD, DC
Posts: 6,207
Default

Another Cantilever Insulation Question


The best option, while still having a chance to prevent condensation, is probably being uninsulated or option 3.

Windows on Wash is offline   Reply With Quote
Old 01-29-2014, 05:33 PM   #3
Newbie
 
Join Date: Jan 2014
Posts: 6
Default

Another Cantilever Insulation Question


Thank you for your reply. I understand that there are two issues here, sealing and insulation and doing either of them wrong will have negative consequences. I went to three difference home building companies today for advice and each of them gave me different answers. I have found different threads on forums and that mention each of my two options.

I was just about to commit to doing it with the xps adhered to the top of the cavity (bottom of the subfloor above) and block it with xps at the entrance to the cantilever (top of the basement wall oposite to the rim joist) but am now doubting myself with your answer. lol.

I guess moisture is one thing, and a cold floor upstairs is another. I haven't had problems with either so far, but that is because it wasn't closed off with a ceiling.

I guess I'm assuming that if I block it off at the start of the cant., then the cold floor issue upstairs will be limited to the 2 feet closest to the wall, which I can live with. It's the moisture issue that I'm not super clear on.
crank73 is offline   Reply With Quote
Old 01-29-2014, 08:44 PM   #4
Registered User
 
Join Date: Mar 2009
Posts: 9,968
Default

Another Cantilever Insulation Question


http://www.buildingscience.com/docum...n-crawlspaces/

http://www.buildingscience.com/docum...al-performance

Foam board the rim also. Plywood over the foam on joist bottoms, air seal it also, but with caulking.

Gary
__________________
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
Old 01-29-2014, 10:21 PM   #5
Newbie
 
Join Date: Jan 2014
Posts: 6
Default

Another Cantilever Insulation Question


Gary, just to confirm then, you would foam 3 of the 4 sides? All but the top (under top floor subfloor)? Or does the rim joice foam foam replace the once at the inside wall end of the cant.?
crank73 is offline   Reply With Quote
Old 01-30-2014, 07:25 PM   #6
Registered User
 
Join Date: Mar 2009
Posts: 9,968
Default

Another Cantilever Insulation Question


If the basement is to be finished (heated), no need to fb the blocking over the bearing wall. If you want dead-air space under decking, fb the block, air-tight.

Gary
__________________
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
Old 01-31-2014, 12:02 AM   #7
Newbie
 
Join Date: Jan 2014
Posts: 6
Default

Another Cantilever Insulation Question


Thanks guys. Gary, the links you provided also answered questions I had reference my next project....dealing with my uninsulated crawlspace. I've got a lot of reading to do. Thanks again.
crank73 is offline   Reply With Quote
The Following User Says Thank You to crank73 For This Useful Post:
Gary in WA (01-31-2014)
Old 02-01-2014, 03:48 PM   #8
Newbie
 
Join Date: Jan 2014
Posts: 6
Default

Another Cantilever Insulation Question


Alright, things are progressing. Last question....for now lol. I am progressing with option 3. 2 in. xps on inside of rim and 2 in. xps on bottom of cavity.

The 3rd diagram above does not show the interior wall that is built in my basement. It was already built and drywalled by previous owners and is 2x4 framing with fiberglass batting and a poly vapour barrier between the frame and the drywall. A couple of inches of poly is sticking out at the top of the wall. The walls were built with a 1 in. (approx) gap between the framing and the concrete wall.

My question is, what length should I cut the xps which is lying in the bottom of my cantilever cavity (3rd picture). Should it end at the outside edge of my concrete wall? Should it end as drawn at the inside edge of my concrete wall? or can I / should I end it at the inside edge of my framed wall?

If it's not at the inside edge of the drywall, should I consider extending the poly that is sticking out of my wall and tacking it to the top of the xps to have a continuous vapour barrier?

Thanks. Back to work.

Last edited by crank73; 02-01-2014 at 03:51 PM.
crank73 is offline   Reply With Quote
Old 02-01-2014, 07:40 PM   #9
General Contractor
 
Gary Evans's Avatar
 
Join Date: Jan 2014
Location: B.C. - Canada
Posts: 110
Default

Another Cantilever Insulation Question


You've got the right idea crank.......insulate against the rim board and the soffit and maintain a small air gap under the rest of the floor.
Where I am minimum is R20 against the rim board and R28 under an cantilever.
I'd go R28 for both in this situation.....but I don't know if you get winter where you are.

The reason for R28 under a cantilever is your feet are far more sensitive to a cold floor than you would be to a cold wall.
If your using laminate flooring I'd go even more......that stuff makes it feel even colder.

Last edited by Gary Evans; 02-01-2014 at 07:44 PM.
Gary Evans is offline   Reply With Quote
Old 02-01-2014, 10:28 PM   #10
Newbie
 
Join Date: Jan 2014
Posts: 6
Default

Another Cantilever Insulation Question


Thanks Gary. I'm in the Edmonton area so winters are pretty cold. How long would you cut the soffit foam board? Flush with the concrete or flush with the interior drywall covering the gap between the studs and the concrete?
crank73 is offline   Reply With Quote
Old 02-02-2014, 06:08 PM   #11
Registered User
 
Join Date: Mar 2009
Posts: 9,968
Default

Another Cantilever Insulation Question


I'd extend it to the face of the drywall for a better air barrier. Leaving a 1" gap between insulation/concrete leads to convective loops, robbing you of R-value and promoting moisture for condensation there (esp. if the cavity is open to wood floor joists above); https://docs.google.com/viewer?a=v&q...fHFsk1RrK9G2HQ
The poly may/may not be fine for the location, compare; ftp://ftp.cmhc-schl.gc.ca/chic-ccdh/..._Web_sept5.pdf

You can lose a lot of R-value with wet insulation; http://archive.nrc-cnrc.gc.ca/eng/ib...ling-heat.html

Gary
__________________
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
Old 02-02-2014, 06:12 PM   #12
General Contractor
 
Gary Evans's Avatar
 
Join Date: Jan 2014
Location: B.C. - Canada
Posts: 110
Default

Another Cantilever Insulation Question


I agree.......bring the insulation to the drywall.
Gary Evans is offline   Reply With Quote
Old 02-02-2014, 10:41 PM   #13
Registered User
 
Join Date: Mar 2009
Posts: 9,968
Default

Another Cantilever Insulation Question


Ah, found the one I was thinking about, middle of the article; http://www.google.com/url?sa=t&rct=j...,d.cGE&cad=rja

Gary

__________________
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
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
Insulating your attic Bob Mariani How To Guides 5 07-07-2013 08:49 PM
Rafter Vents and Insulation nofx1981 Roofing/Siding 15 03-10-2010 08:14 PM
Garage insulation question trojanman1 Building & Construction 7 09-16-2009 02:51 PM
rafter insulation question Jeremy Hillary Boob, PhD Building & Construction 7 08-02-2009 08:19 AM
Insulation Question skavang13 Building & Construction 3 11-16-2008 05:08 PM




Top of Page | View New Posts

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