Go Back   DIY Chatroom Home Improvement Forum > Home Improvement > Building & Construction

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

Reply
 
Thread Tools Search this Thread Display Modes
Old 06-06-2008, 12:10 PM   #1
Power Gen/RS Engineer
 
Join Date: Jun 2006
Location: Oak Park, Illinois
Posts: 751
Rewards Points: 0
Share |
Default

Air cavity required behind spray foam roof insulation


Hey there-

Some time in the fall, I want to convert our attic into a usable space. Since this will become a conditioned space, the insulation plane will need to move from the 2nd story ceiling to the roof line. I had already had some exterior walls insulated with Icynene (none of the walls in my 100 year old house are insulated) as I was remodelling those rooms and I am very happy with the performance of that product, esp. in terms of its effectiveness as an air barrier.

I have done some research and it appears that for cathedral ceilings, the typical insulation details include an air space between the roof sheathing and the ceiling insulation.

1. Will I need to install baffles (or build something similar) on the underside of the roof sheathing before having the Icynene sprayed in?

2. Assuming that I do, it would stand to reason that I would still need soffit and ridge venting?

3. Finally, when this type of conversion is done, is it customary to remove the existing ceiling insulation? I know that I'll need to remove some (it is blown in at a depth of about 3 ft.) in order to deck over the joists but I wanted to know if all the insulation needs to be abated?

My house is located in Illinois, just outside of Chicago.

Thanks!
Jimmy

__________________
Well, now, there's what's right and what's right and never the twain shall meet.
BigJimmy is offline   Reply With Quote
Old 06-06-2008, 02:12 PM   #2
Member
 
Join Date: Jun 2008
Location: Atlanta, GA
Posts: 155
Rewards Points: 0
Default

Air cavity required behind spray foam roof insulation


There are rafter vents that can be stapled to the underside of the roof underlayment which will hold a 1" or 2" (can't remember) void to transfer air from the soffit to a ridge vent or void at the peak. I googled this as an example:

http://www.buildingforhealth.com/pro...hp?prod=ADO-PV

I've seen these at Lowe's and Home Depot. They come in a rigid foam as well as plastic. If it were me, I'd go with plastic since the foam kinda seems like it could be crushed or pierced easily.

jayp is offline   Reply With Quote
Old 06-06-2008, 02:38 PM   #3
Power Gen/RS Engineer
 
Join Date: Jun 2006
Location: Oak Park, Illinois
Posts: 751
Rewards Points: 0
Default

Air cavity required behind spray foam roof insulation


Quote:
Originally Posted by jayp View Post
There are rafter vents that can be stapled to the underside of the roof underlayment which will hold a 1" or 2" (can't remember) void to transfer air from the soffit to a ridge vent or void at the peak.
Yeah, I know what they are and I've seen them at the big boxes. The question was more of whether I need to use them with spray in foam insulation, s'all!
__________________
Well, now, there's what's right and what's right and never the twain shall meet.
BigJimmy is offline   Reply With Quote
Old 06-07-2008, 09:08 PM   #4
Member
 
Join Date: Jan 2007
Posts: 1,787
Rewards Points: 0
Default

Air cavity required behind spray foam roof insulation


The attic gets so hot, and now the attic will be a living space. Is there information on how this spray foam reacts under high temperature and whether it offgasses?
handy man88 is offline   Reply With Quote
Old 06-08-2008, 08:45 AM   #5
Power Gen/RS Engineer
 
Join Date: Jun 2006
Location: Oak Park, Illinois
Posts: 751
Rewards Points: 0
Default

Air cavity required behind spray foam roof insulation


Quote:
Originally Posted by handy man88 View Post
The attic gets so hot, and now the attic will be a living space. Is there information on how this spray foam reacts under high temperature and whether it offgasses?
The product that I've used is called Icynene and as far as I know from talking to the company, there is no restriction to its use for this particular application. That being said, I doubt that it off-gasses but I can check the website where they have all of the technical information.

Here's my real concern. In the winter months (this is northern Illinois), if warm air from the conditioned space leaks into the attic (currently not conditioned), it can condense and cause problems such as mold and possibly rot. When you insulate the inside of the roof, I'm thinking that the air space that you'd create would be to keep both sides of the roof at the same temperature.

Now, for this application, I'm thinking that a vapor barrier would be appropriate which would stop the movement of moist air toward the cold roof. So, basically in this instance, I'm thinking that the baffles/air space would be necessary to deal with any moist air that does leak by. But, in the case of a spray-on foam insulation, one of its benefits is that is completely seals the void and because it is not air permeable, it acts as a complete air-barrier. So, the chances for moist air to actually reach the cold roof sheathing should be pretty much zero. This is why I question that the baffles are needed for this type of insulation material.

The more I research this, I'm finding a lot of differing opinions in the "sealed attic" concept. And yes, I can simply ask the installer for their recommendation or simply go ahead and install the baffles but I want to go into this educated.

Again, I'm not an expert here, just thinking things out. Feel free to chime in!

Jimmy
__________________
Well, now, there's what's right and what's right and never the twain shall meet.
BigJimmy is offline   Reply With Quote
Old 06-08-2008, 09:17 AM   #6
nap
You talking to me?
 
nap's Avatar
 
Join Date: Dec 2007
Location: sw mi
Posts: 5,407
Rewards Points: 0
Default

Air cavity required behind spray foam roof insulation


a totally untrained opinion.


the air space would allow the typical cooling of the roof surface that is designed to prevent ice dams. IF the insulation 100% prevents this, it would be a non-issue.

I also believe it is neccessary due to the fact that even if you prevent all moisture from below, you still have the possibility (actually probability) of leaking from above. Shingles do wear out and there will eventually be leaking. I believe the air space would allow any moisture that does pass through the roof to evaporate out and prevent the wood from being damaged.

This would be similar to the EIFS system problems that happened with sidewalls. EIFS is where they place foam board on the wall and the overcoat with synthetic stucco. Originally, no drains were provided for entrapped moisture and it caused a huge problem with rot in the walls. Eventually, drain systems were employed to prevent this. I would think the roof situation would act in a very similar manner.


but, like I said, merely an untrained observance.
nap is offline   Reply With Quote
Old 06-08-2008, 09:31 AM   #7
Power Gen/RS Engineer
 
Join Date: Jun 2006
Location: Oak Park, Illinois
Posts: 751
Rewards Points: 0
Default

Air cavity required behind spray foam roof insulation


Quote:
Originally Posted by nap View Post
a totally untrained opinion.


the air space would allow the typical cooling of the roof surface that is designed to prevent ice dams. IF the insulation 100% prevents this, it would be a non-issue.
Nap, my electrical pal. Nice to hear your input in a non-electrical forum.

Yes, I totally agree that in a vented attic, the soffit vents allow the cold outside air to cool the inside surface of the roof to keep warm air from melting snow only to have it form as ice when it hits the overhang. But, let's say that you now effectively create a 10" thermal, air-tight barrier between the warm inside space and the freezing outer roof temp. If we can prevent inside thermal energy from melting the snow, we've overcome this issue. I must admit though, it seems strange not to have the air space.

Thanks for the input,
Jimmy
__________________
Well, now, there's what's right and what's right and never the twain shall meet.
BigJimmy is offline   Reply With Quote
Old 06-08-2008, 11:32 AM   #8
nap
You talking to me?
 
nap's Avatar
 
Join Date: Dec 2007
Location: sw mi
Posts: 5,407
Rewards Points: 0
Default

Air cavity required behind spray foam roof insulation


I absolutely agree with you point BUT continue reading my post and you will see that I also am concerned about water infiltration from the outside due to roof damage or shingles wearing out. I would think that water/moisture would need the air space so it can be evaporated out of the wood of the roof. If not, it would simply rot the wood as it would have no place to escape to and no method for drying the wood.

Like I said, this is a totally untrained view but it seems logical to me.
nap is offline   Reply With Quote
Old 06-08-2008, 12:33 PM   #9
Power Gen/RS Engineer
 
Join Date: Jun 2006
Location: Oak Park, Illinois
Posts: 751
Rewards Points: 0
Default

Air cavity required behind spray foam roof insulation


Quote:
Originally Posted by nap View Post
I absolutely agree with you point BUT continue reading my post and you will see that I also am concerned about water infiltration from the outside due to roof damage or shingles wearing out. I would think that water/moisture would need the air space so it can be evaporated out of the wood of the roof. If not, it would simply rot the wood as it would have no place to escape to and no method for drying the wood.

Like I said, this is a totally untrained view but it seems logical to me.
Good point. I'm pretty "untrained" when it comes to this sort of thing as well!
__________________
Well, now, there's what's right and what's right and never the twain shall meet.
BigJimmy is offline   Reply With Quote
Old 06-08-2008, 12:45 PM   #10
nap
You talking to me?
 
nap's Avatar
 
Join Date: Dec 2007
Location: sw mi
Posts: 5,407
Rewards Points: 0
Default

Air cavity required behind spray foam roof insulation


here are a couple videos that from what I can see, do not employ any airspace either in the wall or at the roof.





so maybe I'm ....all wet!

here is another link that speaks to the foam on roof situation:

http://www.askthebuilder.com/565_Foam_Insulation.shtml


After some additional research, it seams icynene is an "open cell" foam and as such, will permit water vapor through so it would seem the foam against the wood my not make any difference. Personallly, I still believe I would consider that air space. Take note of the concern for shingle damage and warranty loss in the ask the builder link.


Last edited by nap; 06-08-2008 at 01:00 PM.
nap 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
Cape Cod Style House Attic/Crawl Space Insulation Help Danielg Insulation 24 05-21-2012 08:20 AM
DIY Spray foam insulation y2khardtop Building & Construction 3 01-12-2008 06:43 PM
Spray in foam insulation leted_82 Building & Construction 3 05-31-2007 10:14 AM




Top of Page | View New Posts

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