Cathedral Ceiling Vent-Barrier-Insulation Question - Insulation - DIY Chatroom Home Improvement Forum


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

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

Reply
 
Thread Tools Display Modes
Old 01-08-2012, 11:14 AM   #1
Newbie
 
Join Date: Jan 2012
Posts: 2
Rewards Points: 10
Default

Cathedral Ceiling Vent-Barrier-Insulation Question


Newbie Here...

I am retrofitting a ranch home in Michigan. Any comments on using a double layer of rigid foam board in a Cathedral Ceiling design as described in the link to the following article? -

http://www.homesandcottages.com/Arti...x?ArticleId=41

I appreciate any comments as I have a very similar situation - I am using 2" rigid foam board with a 1" vent channel from eaves to ridge between every rafter. Then I plan to add batting below the foam.

I am wondering about if/how to seal the joints and seams around the foam board and whether to add more rigid foam board below - and/or a plastic vapor barrier.

I am concerned about the possibility of creating a "vapor sandwich" between the bottom layer of foam and/or plastic and the top layer of foam, with batting in-between.

Additionally, would there be any problem with adding multiple layers of rigid foam directly on top of one another? Would this create a possibility of condensation in-between?

Finally, in using a plastic barrier, what products should I use to seal the overlaps and outer edges?

thanks for your comments! DrMo

Advertisement

DrMo is offline   Reply With Quote
Old 01-09-2012, 11:25 PM   #2
Registered User
 
Join Date: Mar 2009
Posts: 10,007
Rewards Points: 2,080
Default

Cathedral Ceiling Vent-Barrier-Insulation Question


Welcome to the forums!


I couldn't get your link to open.....

Does this cover it?: http://www.buildingscience.com/docum...n-roof-venting

Gary

Advertisement

__________________
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 01-10-2012, 09:43 AM   #3
Exterior Construction
 
Windows on Wash's Avatar
 
Join Date: Aug 2011
Location: Washington DC Metro Area (VA, MD, DC)
Posts: 7,143
Rewards Points: 3,306
Default

Cathedral Ceiling Vent-Barrier-Insulation Question


Quote:
Originally Posted by DrMo View Post
Newbie Here...

I am retrofitting a ranch home in Michigan. Any comments on using a double layer of rigid foam board in a Cathedral Ceiling design as described in the link to the following article? -

http://www.homesandcottages.com/Arti...x?ArticleId=41

I appreciate any comments as I have a very similar situation - I am using 2" rigid foam board with a 1" vent channel from eaves to ridge between every rafter. Then I plan to add batting below the foam.

Don't bother with the vent channels. Make your own out of strips of 1-2" foam. What is the pitch of the roof?

Make sure that the eave and ridge openings are screened to keep the bugs out as well.


I am wondering about if/how to seal the joints and seams around the foam board and whether to add more rigid foam board below - and/or a plastic vapor barrier.

Seal the seams with sealant and/or foam. Foam board will have a higher (XPS and ISO) R-Value per inch so you will get more out of that assembly with foam than you will with fiberglass etc.

Adding a layer of rigid foam to the interior side of the rafters is a great idea because it helps eliminate the thermal bridging of the structure.

Even better is to put the rigid foam to the roof layer but obviously that requires removal of the roof.


I am concerned about the possibility of creating a "vapor sandwich" between the bottom layer of foam and/or plastic and the top layer of foam, with batting in-between.

Use non-vapor barrier (i.e. non foil faced or non poly faced) foams to the outside edge so that it can dry to the vent space and make sure that your air barrier detailing is spot on to the inside.

Additionally, would there be any problem with adding multiple layers of rigid foam directly on top of one another? Would this create a possibility of condensation in-between?

Not if they are sealed up properly.

Finally, in using a plastic barrier, what products should I use to seal the overlaps and outer edges?

If you are using rigid foam to the interior, use a product that has the poly facing and skip the plastic. Acoustical sealant is easy to work with if you go the plastic route. You can also just use a vapor retarder paint when you re-drywall.


thanks for your comments! DrMo
see above...
Windows on Wash is online now   Reply With Quote
Old 01-11-2012, 11:36 AM   #4
Newbie
 
Join Date: Jan 2012
Posts: 2
Rewards Points: 10
Default

Cathedral Ceiling Vent-Barrier-Insulation Question


Thanks for both comments - so far - still would like to hear other thoughts as well...

Gary (GBR in WA) - I am sorry you could not get the link to open - it works for me... Perhaps if you copy and paste into your browser??? The article you provided does not seem to address my situation - not an attic or unvented cathedral roof. Thanks for your efforts!

Windows on Wash - thanks for your detailed response!

I don't know the exact roof pitch, but it is not an extreme slope, typical of a single-story ranch home - very easy to walk on. Good news - I have already installed my own hand-made strips - not the manufactured vent channels.

Can you tell me more about the "product that has the poly facing and skip the plastic" ? Is there a name brand? Finally, where can I purchase the acoustic sealant? Is there a name brand for that as well that you can recommend?

Thanks so much for your input! DrMo
DrMo is offline   Reply With Quote
Old 01-11-2012, 12:03 PM   #5
Member
 
Join Date: Jun 2011
Location: Atlantic Canada
Posts: 379
Rewards Points: 252
Default

Cathedral Ceiling Vent-Barrier-Insulation Question


Windows on Wash has it right. If you go with a thin enough rigid insulation it wont act as a vapour barrier, then you could fill the space with fiberglass and then cover everything with rigid insulation as WoW mentioned. Sometimes you can find (I haven't seen it around here) rigid with a plastic or foil face that acts as a vapour barrier, then you only need to tuck tape the seams. If you go with the 6mil polyethelene sheet, acoustical sealant is a terrible black sticky gooey stuff that will stick the perimeters of the sheet to most surfaces. It can be found at any big box store.
shazapple is offline   Reply With Quote
The Following User Says Thank You to shazapple For This Useful Post:
Noble Bahrs (11-26-2014)
Old 11-25-2014, 05:37 PM   #6
Newbie
 
Join Date: Nov 2014
Posts: 7
Rewards Points: 14
Default

Cathedral Ceiling Vent-Barrier-Insulation Question


How thin should the vented unfaced foam be?
Sandhead is offline   Reply With Quote
Old 11-25-2014, 05:47 PM   #7
Exterior Construction
 
Windows on Wash's Avatar
 
Join Date: Aug 2011
Location: Washington DC Metro Area (VA, MD, DC)
Posts: 7,143
Rewards Points: 3,306
Default

Cathedral Ceiling Vent-Barrier-Insulation Question


Its less a consideration of thickness as compared to facing on the foam. That is the more critical consideration.

EPS is best if you are wanting to keep it vapor open.
Windows on Wash is online now   Reply With Quote
Old 11-25-2014, 08:57 PM   #8
Newbie
 
Join Date: Nov 2014
Posts: 7
Rewards Points: 14
Default

Cathedral Ceiling Vent-Barrier-Insulation Question


How about green guard extruded polystyrene foam from lowes?
Sandhead is offline   Reply With Quote
Old 11-26-2014, 11:36 AM   #9
Exterior Construction
 
Windows on Wash's Avatar
 
Join Date: Aug 2011
Location: Washington DC Metro Area (VA, MD, DC)
Posts: 7,143
Rewards Points: 3,306
Default

Cathedral Ceiling Vent-Barrier-Insulation Question


Check the facing on it and look up the perm rating.
Windows on Wash is online now   Reply With Quote
Old 11-26-2014, 02:25 PM   #10
Newbie
 
Join Date: Nov 2014
Posts: 7
Rewards Points: 14
Default

Cathedral Ceiling Vent-Barrier-Insulation Question


Unfaced Easy to cut and install
Meets all Type IV and Type X specifications. Perm is 1.5

Advertisement

Sandhead is offline   Reply With Quote
Reply

Tags
cathedral ceiling


Thread Tools
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
Another 2x6 cathedral ceiling juststarted Building & Construction 17 11-22-2011 05:27 PM
Cathedral Ceiling Insulation AKHermit Insulation 6 10-16-2011 11:40 PM
Existing Cathedral Ceiling Insulation Question Bob Deb Building & Construction 8 12-07-2010 08:54 PM
Another insulating a cathedral ceiling question. zachalyse Building & Construction 5 06-07-2010 02:17 PM
Type B Vent Question NGuy HVAC 4 08-08-2008 09:04 PM




Top of Page | View New Posts