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 12-19-2011, 09:50 AM   #1
Newbie
 
Join Date: Dec 2011
Location: Ontario, Canada
Posts: 29
Rewards Points: 25
Default

Insulate / vapor barrier drop ceiling question


Apologies if this has been asked 20 times over, but nothing seemed to give me a firm answer. And the fact that I'm going from sub-forum to sub-forum to verify my thinking!

We have a 1960's house with a low slope ceiling, 2x8 construction, currently with R-13 insulation. Room is gutted, and insulation is coming out. This section of the house is the kitchen, and I am installing a drop ceiling to flatten this area, partially for aesthetics, partially to increase insulation values, etc. It will run from the top of the existing exterior wall to the bottom of a 16" beam running the length of the house. Distance is a hair over 8'. 4' of channeling will be placed at the top of the outside wall to allow proper venting in case I cram the insulation too high. Here's a view with details for my question, which I'm afraid I'm over-thinking WAY too much:



It seems from my research that I should place the insulation in zone B (the new drop ceiling), even though this will leave a 14" gap between this insulation and the roof at the top of the slope. In this case, I would also vapour barrier line 2, where IC pot light casings would be, and drywall would be directly on the vapour barrier.

Is this correct, or should I be insulating / adding vapor barrier Zone A / Line 1? This seems to allow a more consistent length of vapor barrier with less chance of damage from sheetrock screws, but is more difficult to tie into the walls' vapor barrier...

If I do the first option, it will be putting 2x10 insulation inside 2x4s, so would the insulation marry above the 2x4s, or will I have 1 1/2" gaps between the insulation that would impact things? Also, would there be a good benefit / price to adding rigid or anything into the Zone A cavity in addition to the R-39 in the drop?

See, major overthinking! Thanks in advance!


Last edited by joeh; 12-19-2011 at 12:13 PM.
joeh is offline   Reply With Quote
Old 12-19-2011, 03:06 PM   #2
Member
 
AGWhitehouse's Avatar
 
Join Date: Jul 2011
Posts: 1,378
Rewards Points: 500
Default

Insulate / vapor barrier drop ceiling question


Insulate B, Vapor Barrier 2...

Insulate around and over beam.

__________________
Life's too short...so enjoy it!
AGWhitehouse is offline   Reply With Quote
The Following User Says Thank You to AGWhitehouse For This Useful Post:
joeh (12-19-2011)
Old 12-20-2011, 09:01 AM   #3
Exterior Construction
 
Windows on Wash's Avatar
 
Join Date: Aug 2011
Location: Washington DC Metro Area (VA, MD, DC)
Posts: 6,633
Rewards Points: 2,548
Default

Insulate / vapor barrier drop ceiling question


What climate zone are you in?

While insulation value can be cumulative if the spaces are connected succinctly, you should make the insulation in one plane.

Climate zone will have everything to do with vapor retarder recommendations.

What is the venting of the current assembly like?

I personally would furr out a vent space in between the joists with some strips of rigid foam, install rigid foam EPS or ISO (install it air tight between the joists) that would serve as both a vent channel with the strips and part of the insulation layer, install additional insulation in between the joists, install rigid foam over the joists to break up the thermal conductance.

Leave all the insulation off surface B. Nothing about drop ceilings are air tight so don't bother with IC cans for that matter.

http://www.buildingscience.com/docum...f-venting/view

Depending on the zone, you may not need to vent but venting is a proven application and if done properly, does not have any real drawbacks in most cases.
Windows on Wash is online now   Reply With Quote
The Following User Says Thank You to Windows on Wash For This Useful Post:
joeh (12-20-2011)
Old 12-20-2011, 09:28 PM   #4
Newbie
 
Join Date: Dec 2011
Location: Ontario, Canada
Posts: 29
Rewards Points: 25
Default

Insulate / vapor barrier drop ceiling question


Quote:
What climate zone are you in?
Sorry, I had read so many people asking where you are and had it in my mind but didn't put it in there. I'm in Canada (Hamilton area, ON), zone B by their standards, zone 5 based on the US map.

Quote:
What is the venting of the current assembly like?
The roof is low pitch (1:10 or so) and venting is through the soffits only along the entire north and south faces of the house. There are no roof vents located anywhere at a higher point to release the hot air. There is a clear run from side to side though - the center 16" beam that supports the roof has the 2x8's sitting on top so air flows over. I don't anticipate changing this anytime soon - flat roof = expensive roofing materials = <3 years old! BUT... recommendations for the future are always welcome!

When I mentioned those roofing channels, I was going to have the clear airflow, but you are recommending actual rigid foam insulation in place of these channels. Understand there. I planned on vapor barrier over the structure, as it's required by the Ontario building code - not sure how the rigid foam over the joists would impact that.

Thanks for the response.

Quote:
Originally Posted by Windows on Wash View Post
What climate zone are you in?

While insulation value can be cumulative if the spaces are connected succinctly, you should make the insulation in one plane.

Climate zone will have everything to do with vapor retarder recommendations.

What is the venting of the current assembly like?

I personally would furr out a vent space in between the joists with some strips of rigid foam, install rigid foam EPS or ISO (install it air tight between the joists) that would serve as both a vent channel with the strips and part of the insulation layer, install additional insulation in between the joists, install rigid foam over the joists to break up the thermal conductance.

Leave all the insulation off surface B. Nothing about drop ceilings are air tight so don't bother with IC cans for that matter.

http://www.buildingscience.com/docum...f-venting/view

Depending on the zone, you may not need to vent but venting is a proven application and if done properly, does not have any real drawbacks in most cases.
joeh is offline   Reply With Quote
Old 12-21-2011, 07:37 AM   #5
Exterior Construction
 
Windows on Wash's Avatar
 
Join Date: Aug 2011
Location: Washington DC Metro Area (VA, MD, DC)
Posts: 6,633
Rewards Points: 2,548
Default

Insulate / vapor barrier drop ceiling question


Rigid foam, depending on the type, does qualify as a Class I vapor retarder (i.e. vapor barrier with less than 0.1 vapor permanence).

I think all the solutions for your roofing/insulation quandary are in that link I posted.

I would run the rigid foam, make your own vent chutes, and supply some ventilation exhaust on the top side of the home.
Windows on Wash is online now   Reply With Quote
The Following User Says Thank You to Windows on Wash For This Useful Post:
joeh (12-21-2011)
Old 12-21-2011, 08:57 AM   #6
Member
 
AGWhitehouse's Avatar
 
Join Date: Jul 2011
Posts: 1,378
Rewards Points: 500
Default

Insulate / vapor barrier drop ceiling question


Quote:
Originally Posted by Windows on Wash View Post
Rigid foam, depending on the type, does qualify as a Class I vapor retarder (i.e. vapor barrier with less than 0.1 vapor permanence).
Polyisocyanurate foam board is what you will need to achieve the Class I vapor retarder rating. XPS foam is too permeable and would take a large thickness to reach the permeability rating of a Class I vapor retarder. EPS is not even an option when a Class I foam is needed.
__________________
Life's too short...so enjoy it!
AGWhitehouse is offline   Reply With Quote
Old 12-21-2011, 09:43 AM   #7
Exterior Construction
 
Windows on Wash's Avatar
 
Join Date: Aug 2011
Location: Washington DC Metro Area (VA, MD, DC)
Posts: 6,633
Rewards Points: 2,548
Default

Insulate / vapor barrier drop ceiling question


Quote:
Originally Posted by AGWhitehouse View Post
Polyisocyanurate foam board is what you will need to achieve the Class I vapor retarder rating. XPS foam is too permeable and would take a large thickness to reach the permeability rating of a Class I vapor retarder. EPS is not even an option when a Class I foam is needed.
Polyiso with a foil facer will give you the Class I vapor retarder as will XPS with a poly facer.

EPS can be had with a foil facer as well which makes it class I but you would never use it in this case because of the lower R-Value per inch.

Might as well use ISO because it is the "greenest" of the foams and gives you the highest R-Value per inch.

If the roof is going to remain vented, the permeance of the foam is less of an issue as compared to the airtighness of the ceiling/foam assembly. Airtightness is far more critical in this case as any diffused moisture through a tight, painted drywall ceiling should be removed by the venting.
Windows on Wash is online now   Reply With Quote
Old 12-21-2011, 09:49 AM   #8
Member
 
AGWhitehouse's Avatar
 
Join Date: Jul 2011
Posts: 1,378
Rewards Points: 500
Default

Insulate / vapor barrier drop ceiling question


Quote:
Originally Posted by Windows on Wash View Post
as will XPS with a poly facer.
Haha, I agree...facings are definately a game changer on permeability. My post's information was for unfaced foam boards.
__________________
Life's too short...so enjoy it!
AGWhitehouse is offline   Reply With Quote
Old 12-21-2011, 09:50 AM   #9
Exterior Construction
 
Windows on Wash's Avatar
 
Join Date: Aug 2011
Location: Washington DC Metro Area (VA, MD, DC)
Posts: 6,633
Rewards Points: 2,548
Default

Insulate / vapor barrier drop ceiling question


Quote:
Originally Posted by AGWhitehouse View Post
Haha, I agree...facings are definately a game changer on permeability. My post's information was for unfaced foam boards.


I know that you know this stuff backwards and forwards. Just clarifying for the customer's sake.
Windows on Wash is online now   Reply With Quote
Old 01-10-2012, 10:56 PM   #10
Newbie
 
Join Date: Dec 2011
Location: Ontario, Canada
Posts: 29
Rewards Points: 25
Default

Insulate / vapor barrier drop ceiling question


Whew, you guys started talking over my head, but I think I'm finally caught up! And FINALLY onto the insulation process, as the process fell behind a bit.

I have listened to everything and read the sheet, and have come to a plan of attack, and wanted to bounce it off of you all.

First off, I picked up some cheap EPS insulation and cut furring strips to place between the ceiling joists. 1 1/2" to start, moved to 2" quickly - I wanted to make sure I could fit 2x6 insulation in at the lowest slope, and needed that 1 1/2" gap. I'm currently installing 1" EPS, ripped to pressure fit, into the joists to form my channel. Question 1:
  • When I read the instructions for the cheap stuff, they said to leave gaps between 4' pieces - is that still the case here? I have those X supports that form a perfect break, and would be hard to seal up if there is not supposed to be a gap.
I have 2" EPS that will be doubled or tripled up and placed into the cavity under the vent channel on top of the frame wall. So R-20-30 of insulation there.

Next, I'll be using fiberglass into the joist cavity. Easy.

Now, you mention placing the thermal break of rigid insulation on the sloped ceiling to keep away from using IC boxes on my potlights, but this just won't work. My drawing wasn't very well to scale, and this is a BIT better, still not there though:





My actual dimensions are of a 10'6" 2x6 drop ceiling, so around 5'6" overlap, while only the last 5 feet have a gap between the drop joists and the sloped joists. I believe that you said I should place the thermal break to the top side of the letter "A". I just don't see how that can work.

So... my plan, unless you convince me otherwise, is to fill with fiberglass batts, insulate the walls, bringing vapor barrier around onto the ceiling, and then place 1/2" thick faced PolyISO IsoGard onto the flat ceiling, taping all seams to form a vapor barrier. Is this just too much work for 1/10 of the surface area of the roof?


Last edited by joeh; 01-10-2012 at 11:08 PM.
joeh 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
Basement ceiling question aggst1 Remodeling 9 05-07-2013 03:23 PM
More Basement Dropped Ceiling Installation Questions markronz Remodeling 7 02-28-2010 03:47 PM
Cans in a drop ceiling with 4" clearence RegeSullivan Electrical 3 04-27-2009 10:55 AM
Ceiling fan + potentiometer question mothra Electrical 4 04-21-2009 01:11 PM
Question about ceiling joists... StlJoe Building & Construction 5 12-06-2005 11:52 AM




Top of Page | View New Posts

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