Knee Wall Insulation?

 
Thread Tools Search this Thread Display Modes
Old 02-09-2009, 03:43 PM   #1
Pro
 
MEL's Avatar
 
Trade: Roofing
Join Date: Apr 2007
Location: Detroit
Posts: 576

Knee Wall Insulation?


What is the best way to insulate a knee wall? I have a customer with a bungalow that is about 50 years old. A bungalow is a type of house with a bedroom up stairs and part of the ceiling is angled like the roof.

The angled part of the ceiling is insulated and has an air space for ventilation.

The knee wall is already insulated with 3.5” fiberglass with a foil face. The foil is facing the cold side of the wall.

The customer wants me to add insulation to this wall. What would be the best way to it?

I am going to be adding 17” blown in fiberglass to the attic behind the knee wall. I’m also going to be adding soffit vents, baffles and ridgevent.

I would appreciate a quick response; the customer is waiting for me to call back with a price.

__________________
MEL
MEL is offline  
Warning: The topics covered on this site include activities in which there exists the potential for serious injury or death. ContractorTalk.com DOES NOT guarantee the accuracy or completeness of any information contained on this site. Always use proper safety precaution and reference reliable outside sources before attempting any construction or remodeling task!

Old 02-09-2009, 04:38 PM   #2
Pro
 
MEL's Avatar
 
Trade: Roofing
Join Date: Apr 2007
Location: Detroit
Posts: 576

Re: Knee Wall Insulation?


The existing insulation on the knee wall has the vapor barrier facing out. In Michigan the vapor barrier should be on the warm side, facing in. Should I rip it out?

Would I create a bigger problem if I insulate over it with another vapor barrier?

What about adding Foamboard insulation?
__________________
MEL
MEL is offline  
Old 02-09-2009, 05:43 PM   #3
Sean
 
SLSTech's Avatar
 
Trade: General Contractor
Join Date: Sep 2008
Location: Cullman, AL
Posts: 4,513
Send a message via Skype™ to SLSTech

Re: Knee Wall Insulation?


Mel, I don't know if it is the best - but regular batt insulation in the knee wall cavities would be my answer at the moment. (Sorry, but I mainly push / spec closed cell spray foam with no ventilation for the roofs, walls sprayed foam & use batt insulation on interior walls to help with noise) You could put rigid insulation on the back of the wall but I would think that would be a pain.
SLSTech is online now  
Old 02-09-2009, 05:57 PM   #4
Capra aegagrus
 
Tinstaafl's Avatar
 
Trade: Remodeler
Join Date: Jan 2008
Location: Central Pennsylvania
Posts: 9,749

Re: Knee Wall Insulation?


I too (without seeing it) would go with batts on the knee wall. Definitely get rid of that inside out vapor barrier. Installing the batts from the "wrong" side of the wall makes the new vapor barrier a bit tough to get any kind of seal. Maybe some tightly fitted foam board installed and foamed tight prior to the batts would be the best compromise, then use unfaced batts.
Tinstaafl is offline  
Old 02-09-2009, 08:13 PM   #5
Pro
 
Kgmz's Avatar
 
Trade: General, Electrical, and Plumbing Contractor
Join Date: Feb 2007
Location: Portland, OR & Eatonville, WA
Posts: 1,264

Re: Knee Wall Insulation?


The best way is as SLSTech mentioned with the roof inulated all the way to the outside wall.

The problems with this type of construction with the knee walls, lower ceiling in below attic out to outside wall and roof above upstairs space. Is that you have cold air coming in at the soffit and supposedly going out ridge, but sometimes it will infiltrate through the knee wall insulation if it is not tight and sealed and then with the cold air hitting the back of the sheetrock you will have condensation there. And with batts faced or unfaced you do not get a tight seal with 2x4 studs and then if you put in a thicker batt then you have the gap where the studs are not out as far as the insulation. Also don't forget to seal off the space under the floor from the attic, you don't want cold air blowing under there.

I have built several of these type of bungalows, room in attic. What we used to do. Solid blocking under wall in joist space to reduce air inflitration under floor and blocking out from top of knee wall to hold ceiling insulatiion and to give a place to attach foam board. Knee wall gets 3.5" batts and cover wall in attic space with 1.5 or 2 " foam board running it up in to rafter space fitted around rafters leaving a 1" gap for ventilation and all the way down to sheetrock of ceiling below fitting it in between the ceiling/floor joists. And then some canned foam to fill in any gaps and tape seams. And then blown in for the ceiling below attic space. This will reduce any chance of air infiltration on that wall.

What we do now, spray foam either closed roof or under ventilation space built under roof. And then this conditioned attic space is sheetrocked and used as storage if stick built or just left as is if trusses. And way better overall if there is any ductwork in there.
Kgmz is offline  
Old 02-09-2009, 08:59 PM   #6
Pro
 
MEL's Avatar
 
Trade: Roofing
Join Date: Apr 2007
Location: Detroit
Posts: 576

Re: Knee Wall Insulation?


Quote:
Originally Posted by Kgmz View Post
The best way is as SLSTech mentioned with the roof inulated all the way to the outside wall.

The problems with this type of construction with the knee walls, lower ceiling in below attic out to outside wall and roof above upstairs space. Is that you have cold air coming in at the soffit and supposedly going out ridge, but sometimes it will infiltrate through the knee wall insulation if it is not tight and sealed and then with the cold air hitting the back of the sheetrock you will have condensation there. And with batts faced or unfaced you do not get a tight seal with 2x4 studs and then if you put in a thicker batt then you have the gap where the studs are not out as far as the insulation. Also don't forget to seal off the space under the floor from the attic, you don't want cold air blowing under there.

I have built several of these type of bungalows, room in attic. What we used to do. Solid blocking under wall in joist space to reduce air inflitration under floor and blocking out from top of knee wall to hold ceiling insulatiion and to give a place to attach foam board. Knee wall gets 3.5" batts and cover wall in attic space with 1.5 or 2 " foam board running it up in to rafter space fitted around rafters leaving a 1" gap for ventilation and all the way down to sheetrock of ceiling below fitting it in between the ceiling/floor joists. And then some canned foam to fill in any gaps and tape seams. And then blown in for the ceiling below attic space. This will reduce any chance of air infiltration on that wall.

What we do now, spray foam either closed roof or under ventilation space built under roof. And then this conditioned attic space is sheetrocked and used as storage if stick built or just left as is if trusses. And way better overall if there is any ductwork in there.
Can I just leave the foil faced insulation alone if there are no sign of mildew?

What would happen if I put foamboard over it?

Could I put tyvek over the batts to cut down air infiltration?
__________________
MEL

Last edited by MEL; 02-09-2009 at 09:01 PM.
MEL is offline  


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes Rate This Thread
Rate This Thread:

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
Knee Wall Framing rstork Framing 32 01-04-2009 10:22 PM
In Wall Insulation eoffmasonry Masonry 2 08-28-2008 08:36 PM
Radiant Barrier Fact Sheet Ed the Roofer Roofing 0 02-09-2008 08:57 PM
Knee Wall Insulation ? baspinall General Discussion 1 10-07-2006 07:21 PM
Knee wall Insulation ? baspinall HVAC 0 10-07-2006 10:39 AM

Join Now... It's Fast and FREE!

Privacy Badge
I am a professional contractor
I am a DIY Homeowner
ContractorTalk.com is for
PROFESSIONAL CONTRACTORS ONLY!

At ContractorTalk.com we cater exlusivly to professional contractors who make their living as a contractor. Knowing that many homeowners and DIYers are looking for a community to call home, we've created www.DIYChatroom.com DIY Chatroom is full of helpful advices and perfect for DIY homeowners.

Redirecing in 10 seconds
No Thanks
terms of service

Already Have an Account?