Insulating Vaulted Ceilings - Insulation - DIY Chatroom Home Improvement Forum

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


Thread Tools Search this Thread
Display Modes
Old 12-01-2015, 10:01 PM   #1
Join Date: Jul 2007
Location: Seattle WA
Posts: 582
Rewards Points: 444

Insulating vaulted ceilings

I live in Portland Oregon and I did a second-story addition that has 2 x 12 vaulted ceilings. I plan to put in high density R-38 and I have a continuous ridge vent at the peak. I will have 1" plastic baffles from the bird locks to the peaks and most ceiling rafters are 24 on center.

My question is related to what should I do about the vapor barrier options.

I could get unfaced batts, or Kraft faced batts.

If I get the Kraft faced batts, then all I have to do is put them up and I'm done with the vapor barrier basically.

If I put up the unfaced batts, then it seems like I have the option of putting a four-mil plastic vapor barrier or over the ceiling surface or I can do some kind of spray on vapor barrier.

I kind of like the idea of the Kraft faced batts because it seems like having a little bit of breathing around the edges might not be a bad idea, but all the installers seem like they'll do a plastic thing to save cost and time..

I've also toyed with the idea of going with unfaced batts and doing plastic on the lower part but putting tyvek at the peaks for a little bit of breathing for any moisture that gets stuck in the peaks..

Basically I'm not sure what the goal is and what the best way to achieve it would be..

I had a problem before in my vaulted ceiling where water would condense on the roof sheeting when it would freeze and then when it got above freezing the water would run down the ceiling and drip on the floor.

My father inlaw had a problem on his vaulted ceiling where water would condence on the ceiling and mold would form because there was no attic ventilation.. Seems like if I put in a solid vapor barrier I'd have the mold problem..


Last edited by zootjeff; 12-01-2015 at 10:06 PM.
zootjeff is offline   Reply With Quote
Sponsored Links
Old 12-02-2015, 04:42 AM   #2
Exterior Construction
Windows on Wash's Avatar
Join Date: Aug 2011
Location: Washington DC Metro Area (VA, MD, DC)
Posts: 26,042
Rewards Points: 878
Blog Entries: 41

Once the Kraft facing is stapled to the stud and covered with drywall, there is little to no breathing up there.

Here is what I think is one of the better articles on roof venting:
Windows on Wash is offline   Reply With Quote
Sponsored Links
Old 12-02-2015, 07:25 AM   #3
Join Date: Nov 2015
Location: Maine
Posts: 10,676
Rewards Points: 154

The problem your fil had with condensation at the peak of his vaulted ceiling was simply cold drywall and humid air. Two things in play here, moist air is lighter than dry air, so along with warm air being lighter, the higher moisture is up there as well. Then, few vaulted ceilings have sufficient insulation. Remember, code level requirements are NOT the best, they are bare minimum. Add in that fiber insulation is very susceptible to air circulation and often performs below its sticker value.

We are still in an age where we are testing by trial and error on how best to insulate vaulted ceilings. IMO, I like a couple of inches of rigid foam board installed to form the vent channel with 1.5 to 2" of vent space. Then fill with Roxul and if code requires, a vapor barrier. Personally, I used plastic vapor barriers long before they became unpopular and they did fine, but I'm not in your climate zone. Check local requirements.

Bud9051 is offline   Reply With Quote
Sponsored Links

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
Vaulted Ceiling - Insulating & Removal of Ceiling Joists hammertyme Insulation 8 12-10-2014 09:40 PM
Insulating Low Pitched Roof with Vaulted Ceilings Inside BlakeL Insulation 15 05-24-2013 09:00 PM
Vaulted ceilings and returns.. valcarmo72 HVAC 8 05-17-2013 06:43 AM
insulating conundrum 2X8 Cathedral Ceilings rudy2262 Insulation 2 04-08-2013 08:23 PM
Ridge vent over vaulted ceilings? EC1970 Roofing/Siding 1 01-08-2011 06:35 AM

Top of Page | View New Posts