Welcome to the DoItYourself Forums!

To post questions, help other DIYers and reduce advertising (like the one on your left), join our DIY community. It's free!

Faced or unfaced insulation? Vapor barrier?


ethan169's Avatar
Member

Join Date: Dec 2010
Posts: 66
CT

07-23-12, 10:39 AM   #1  
Faced or unfaced insulation? Vapor barrier?

So I have a 1910 cape and im doing a complete gut and remodel on the kitchen. Ive removed all of the plaster (walls and ceiling) and removed the little blown in insulation that was there. About 30% of the kitchen has exterior walls and id like to insulate. Im also putting new windows in.

Heres the question... Do I want a vapor barrier? Do I use unfaced fiberglass batt R15 and put plastic over it? Or do I use faced batt and omit the plastic? Does the paper actually act a vapor shield? I thought it didnt? My contractor friend says it does.

Thanks for the help!

 
Sponsored Links
stickshift's Avatar
Group Moderator

Join Date: Oct 2004
Posts: 18,476
WI

07-23-12, 10:45 AM   #2  
Either is fine - place the vb to the inside since you're in a cold weather state.

 
ethan169's Avatar
Member

Join Date: Dec 2010
Posts: 66
CT

07-23-12, 10:53 AM   #3  
Thanks Mitch. Just to confirm. The paper faced batt insulation does not need an additional plastic barrier stapled over it? Id rather use this as it seems it would be quicker to install.

Thanks again.

 
Furd's Avatar
Member

Join Date: Mar 2006
Posts: 18,332
WA

07-23-12, 10:56 AM   #4  
I suggest the plastic sheeting over the entire wall after installing unfaced fiberglass. That way you can more carefully cut out and seal around electrical boxes and the like. Be sure to tape all seams.

I personally don't like fiberglass as it is finicky about installation requiring it not be be compressed yet still fill all voids. Fiberglass does nothing as far as controlling air movement so be sure to completely seal any penetrations where pipes or wires are located with expanding foam or fire caulk. Also, seal all openings into the the electrical boxes with fire rated caulk.

 
Nashkat1's Avatar
Member

Join Date: Mar 2012
Posts: 8,470
VA

07-23-12, 11:57 AM   #5  
Heres the question... Do I want a vapor barrier? Do I use unfaced fiberglass batt R15 and put plastic over it? Or do I use faced batt and omit the plastic? Does the paper actually act a vapor shield? I thought it didnt? My contractor friend says it does.
You're both right! Seriuusly. I depends on which paper the batts are faced with.

If the paper is coated with asphalt on the side next to the fiberglass, than that is the vapor retarder and no other barrier should be installed over it. But if the paper looks the same on both sides, then there isn't a vapor retarder, and a different material may be installed over it. In your area, I would definitely install one of the two.

My favorite method is to install the plain-paper-faced batts, taking the time to carefully trim and fit them around any electrical boxes or other obstructions and making sure to keep them at least 1" off the outside wall. When they are all in, I slash the paper facing with several long cuts, just to make sure that it can't hold vapor.

Then I hang 10mil poly over the entire wall, letting it lap a few inches onto the floor and the ceiling, if possible. I cut an "X" inside each electrical box, then hang the drywall, then trim the plastic out of the windows.

Either way, you need one, and only one, layer of vapor retarder, at the interface between the interior wall finish and the framing/insulation.

 
ethan169's Avatar
Member

Join Date: Dec 2010
Posts: 66
CT

07-23-12, 12:22 PM   #6  
Thank you both for the information.

My favorite method is to install the plain-paper-faced batts, taking the time to carefully trim and fit them around any electrical boxes or other obstructions and making sure to keep them at least 1" off the outside wall
So i need to ensure that there is a 1" gap between the insulation and the exteripr sheathing? I was't aware of this. What R value can I use then? I was thinking of using R15?

Thanks,

 
Nashkat1's Avatar
Member

Join Date: Mar 2012
Posts: 8,470
VA

07-23-12, 12:57 PM   #7  
What R value can I use then? I was thinking of using R15?
You should enter the specific information for your house into the ZIP-Code Insulation Program to learn the optimum value. That said, I entered some generic information for an existing wood-framed house in ZIP Code 060nn and got R-11 for the walls.

Different question: Does your kitchen have double-hung sash windows balanced with counter-weights that run in an open channel next to each window? If so, have you thought about a way to seal and/or insulate those channels?


Last edited by Nashkat1; 07-23-12 at 01:00 PM. Reason: to add link.
 
ethan169's Avatar
Member

Join Date: Dec 2010
Posts: 66
CT

07-23-12, 01:09 PM   #8  
I entered the information into this site and it comes back with R-11. However it does not ask me what kind of construction the house is. 2x4 or 2x6 or 2x3 even? How does it know? why would R-11 be better then R-13 if I can fit it in?

As for the windows your exactly right. There are replacements in the old frames that you have described. I am replacing them with new construction Jled-wen casement windows. I have some non expanding spray foam and batt insulation if I need. That was my thoughts on it anyway.

 
stickshift's Avatar
Group Moderator

Join Date: Oct 2004
Posts: 18,476
WI

07-23-12, 01:16 PM   #9  
Yes, R-13 would be better than R-11 if the batts fit into the cavities without being compressed.

 
ethan169's Avatar
Member

Join Date: Dec 2010
Posts: 66
CT

07-23-12, 01:18 PM   #10  
Ok, What about the 1" gap required from the exterior sheathing? Did i miss understand here?

Thanks again for all your help

 
Furd's Avatar
Member

Join Date: Mar 2006
Posts: 18,332
WA

07-23-12, 01:29 PM   #11  
Air, including moisture-laden air, travels freely through fiberglass insulation. There is no need for any clearance between the fiberglass and the exterior wall.

 
ethan169's Avatar
Member

Join Date: Dec 2010
Posts: 66
CT

07-23-12, 01:33 PM   #12  
Ah I understand now. Thanks again!

 
Nashkat1's Avatar
Member

Join Date: Mar 2012
Posts: 8,470
VA

07-23-12, 01:59 PM   #13  
Ok, What about the 1" gap required from the exterior sheathing? Did i miss understand here?
I think you understood correctly. There needs to be enough space behind the "insulation" for air to travel freely and for moisture to wick into. In fact, make sure the outside wall can breathe.

The reason I put "insulation" in quotes above is that the real insulation is dry, still air. The stuff we install, and call "insulation," is a product we've designed to trap the air and hold it in place.

Air does not travel freely through fiberglass insulation. Moisture does, although slowly, as it does through ant open-cell insulation. If it didn't, the insulation would become sodden and lose it's R-value, not to mention harboring mold.

There is no need to install anything more than R-11. That program is designed to return the most cost-effective result for the specific situation it is analyzing. Installing more reduces the return on investment. In addition, less insulating material plus a larger ventilation channel almost always produces a more effective building envelope.

As for the windows your exactly right. There are replacements in the old frames that you have described. I am replacing them with new construction Jled-wen casement windows.
Sounds like your originally had sash-over-sash windows, and won't now. So you won't need my hard-won advice on how to reduce air infiltration and heat loss through those channels while restoring the counterweight system. Oh, well.

 
ethan169's Avatar
Member

Join Date: Dec 2010
Posts: 66
CT

07-23-12, 02:37 PM   #14  
ha! Now i think I understand. R-11 it is. Either way im sure it will be 100x better then nothing.

As for your experience on the sash over sash windows I still have 16 or so other windows that im not replacing . Id be very interested in your tips and tricks with these as a few of them are drafty.

Thanks again NashKat

 
drooplug's Avatar
Member

Join Date: Aug 2009
Posts: 4,940
NJ

07-23-12, 03:46 PM   #15  
I think you understood correctly. There needs to be enough space behind the "insulation" for air to travel freely and for moisture to wick into. In fact, make sure the outside wall can breathe.
This is very wrong information. Install R-13 batts. You do not want an air gap between the insulation and sheathing. Are will convect in the space and reduce the R value of the batt. Fiberglass insulation does not stop air flow. Air will move through it with no problem. That air will reduce R-value and clog your fiberglass with dirt and that further reduces R-value over time.

EDIT: The only time you want an air gap is between insulation and roof sheathing.

buildingscience.com is your friend. There is a lot of information there about vapor barriers and insulation and many other things.

 
Furd's Avatar
Member

Join Date: Mar 2006
Posts: 18,332
WA

07-23-12, 04:20 PM   #16  
Air does not travel freely through fiberglass insulation. Moisture does, although slowly, as it does through ant open-cell insulation. If it didn't, the insulation would become sodden and lose it's R-value, not to mention harboring mold.

There is no need to install anything more than R-11. That program is designed to return the most cost-effective result for the specific situation it is analyzing. Installing more reduces the return on investment. In addition, less insulating material plus a larger ventilation channel almost always produces a more effective building envelope.
You're certainly entitled to your opinion but trust me, air travels freely through properly installed (uncompressed) fiberglass. It is because of this that housewrap was developed, to stop the airflow. Stopping airflow is as important as the insulation itself in keeping the interior comfortable.

When installing an inexpensive material like fiberglass insulation, more is almost always cost effective when done initially. Retrofitting insulation in a home already built is rarely cost effective unless you plan on amortizing the cost over about a forty year period. Retrofitting windows is just about as bad if the primary reason is to save money. The more energy prices rise, the faster the payback for increased insulation, better insulation and especially air sealing.

 
drooplug's Avatar
Member

Join Date: Aug 2009
Posts: 4,940
NJ

07-23-12, 04:26 PM   #17  
The best option for these walls would be to spray 2" of closed cell spray foam. That is expensive though. A lower cost option would be to spray in open cell spray foam and cover it with a plastic VB. They both do a tremendous job of air sealing. The advantage of closed cell is that it forms a VB at 2" and has double the R-value per inch.

 
Nashkat1's Avatar
Member

Join Date: Mar 2012
Posts: 8,470
VA

07-23-12, 08:43 PM   #18  
This is very wrong information.
Not in my experience.

Install R-13 batts. You do not want an air gap between the insulation and sheathing. Are will convect in the space and reduce the R value of the batt. Fiberglass insulation does not stop air flow. Air will move through it with no problem. That air will reduce R-value and clog your fiberglass with dirt and that further reduces R-value over time.
This, on the other hand, is inaccurate information - in my experience. The air flow inside a wall is minimal, but, in a well-constructed enclosure, it is enough to allow the moisture to be effectively removed.

 
ethan169's Avatar
Member

Join Date: Dec 2010
Posts: 66
CT

07-24-12, 06:18 AM   #19  
I went to home depot yesterday to research some insulation prices.

Just as a note the information in the pamphlet says for my area to install R-13 or R15 fiberglass insulation for 2x4 walls. Both R-13 and R-15 have a thickness of 3 1/2 inches according to the package. R-15 is obviously a little more expensive. Either way at 3 1/2 inches its fills most of if not all of the wall cavity. They do not sell R-11 in the store from what I could tell. I am in New England so of course more insulation is better in my mind.

drooplug
The best option for these walls would be to spray 2" of closed cell spray foam. That is expensive though. A lower cost option would be to spray in open cell spray foam and cover it with a plastic VB. They both do a tremendous job of air sealing. The advantage of closed cell is that it forms a VB at 2" and has double the R-value per inch.
Unfortunately I dont think this would be worth it. Im only doing the kitchen and this is only 2 exterior walls. The rest of the house will remain the same. If its anything like the kitchen was then there is blown in insulation but a hand full of sections without it due to the fire stops. (I have balloon frame construction)

I figure since I am replacing both windows in this room and removing all of the old blown in insulation and re installing fiberglass R-13 or R-15 on all of the exterior walls this room will be 100% better then it was. I do however understand that the rest of the house is the same that it was. And I have reduced a wall between the kitchen and living too 45" tall so its more of an open floor plan. I think it would be a waste to go crazy on insulating just this one room.

Anyway I will do some more research and report back. I have too many contradicting opinions right now. This building science website seems interesting. Ill report back with some more info and possibly a pic or two when Im finished.

Thanks again

 
drooplug's Avatar
Member

Join Date: Aug 2009
Posts: 4,940
NJ

07-24-12, 02:40 PM   #20  
This, on the other hand, is inaccurate information - in my experience. The air flow inside a wall is minimal, but, in a well-constructed enclosure, it is enough to allow the moisture to be effectively removed.
You may want to read some of the research at buildingscience.com.

 
drooplug's Avatar
Member

Join Date: Aug 2009
Posts: 4,940
NJ

07-24-12, 02:43 PM   #21  
Unfortunately I dont think this would be worth it. Im only doing the kitchen and this is only 2 exterior walls. The rest of the house will remain the same. If its anything like the kitchen was then there is blown in insulation but a hand full of sections without it due to the fire stops. (I have balloon frame construction)
It's up to you if you want spend the extra money. I'm not sure having the batts will be much of an improvement over the blown in. The exception to that would be the areas that didn't have insulation. I'm not saying the batts are bad. Just that the spray foam is an improvement over the batts. Even though you won't be doing the whole house, it would be worth the expense, in my opinion, if you have the money to do it.

 
ethan169's Avatar
Member

Join Date: Dec 2010
Posts: 66
CT

07-25-12, 07:47 AM   #22  
So I did some reading of a few articles posted at that buildingscience.com website. Interesting stuff.

Here is a quote from:
Building American Special Research Project: High-R Walls Case Study Analysis
Neither cellulose nor fiberglass batt is an air barrier, so an air barrier should always be used with either insulation.
According to these guys air does flow through fiberglass insulation etc.

A somewhat unrelated question. At Home depot they have R-13 precut bats (92" I think) and then they have rolls of 32' I want to say. The rolls are compressed in a ball and considerably smaller in packaged size then the precut lengths. But there is more and they are cheaper. Also the thickness is still 3.5" on the rolls.

Is there a reason to not get the rolls over the precut lengths? Especially since the precuts are shorter then my 9' ceilings?

Thanks again

 
Nashkat1's Avatar
Member

Join Date: Mar 2012
Posts: 8,470
VA

07-25-12, 12:13 PM   #23  
At Home depot they have R-13 precut bats (92" I think) and then they have rolls of 32' I want to say. The rolls are compressed in a ball and considerably smaller in packaged size then the precut lengths. But there is more and they are cheaper. Also the thickness is still 3.5" on the rolls.

Is there a reason to not get the rolls over the precut lengths? Especially since the precuts are shorter then my 9' ceilings?
I would definitely get the rolls. The precut 92" batts are made to go with precut 92" studs for 8' walls.

To answer a question that I meant to get to earlier:
However it does not ask me what kind of construction the house is. 2x4 or 2x6 or 2x3 even? How does it know?
The ZIP-Code Insulation Program doesn't know how deep your stud bays are. It doesn't ask you about stud depth because it doesn't matter. What matters is the type of construction, which it does ask for - basically, is whether it has wood or metal framing. Separately, it has an option where you can ask for advice on insulating your masonry walls, if you have those.

The real calculation is actually a piece of calculating the R-value of the finished assembly, which is the answer that's important. This program, and most others like it, make some assumptions, such as taking the interior finish material to be 1/2" gypsum board (drywall). Since drywall has an R-value of 0.9/in., using 5/8" board instead of 1/2" adds 0.11 to the R-value of the assembly. Paneling the room, or blowing insulation in behind a plaster wall, will produce a different result.

Note: This doesn't mean that the R-value of a finished assembly is the sum of the R-values of its components. It isn't.

why would R-11 be better then R-13 if I can fit it in?
I think I answered earlier that adding extra insulation starts to lower the return on investment. That's true, of course, but I'm imagining that the difference in cost between R-11 (if you could find it) and R-13 is very small.

Here's something that I found interesting: I just ran the calculator again, and got R-13 for the framed exterior walls. And I know why. This time, I deliberately dropped the efficiency of the made-up central gas furnace from High to Medium, just to see if that would make a difference. And it did.

 
GBR in WA's Avatar
Member

Join Date: Mar 2009
Posts: 1,167
WA

07-25-12, 07:56 PM   #24  
You didnít mention the siding type or design, or if there is foam board on the outside, it makes a big difference on the vapor barrier Class: Info-310: Vapor Control Layer Recommendations — Building Science Information

Notice in that link, the asphalt paper faced batt is fine for your location (Zone 5), safer than plastic sheeting (used on indoor pools and saunas). Simply slashing any vapor barrier/retarder is almost useless as they are area-weighed (linear) unlike an air-barrier; Air Barrier or Vapor Barrier? - Building Science Podcast | GreenBuildingAdvisor.com

With a wet siding outside the cavity and moisture leakage to the cavity insulation, expect R-12 reduced to R-4 (a 60-70% loss) just from the day/night cycle changes: Info-310: Vapor Control Layer Recommendations — Building Science Information
Be sure to canned-foam seal the wiring/plumbing holes through the plates and studs, caulk the sheathing to the plates/studs and caulk the bottom plate to sub-floor joint. ADA the drywall: Info-401: Air Barriers

The R-11 was recommended by the DOE site because it hasnít up-dated the original info (from 2008) that R-13 is required per minimum IRC Code since 2006, and R-11 isnít even carried in the local box stores as it wonít pass basic minimum insulation requirements; Chapter 11 - Energy Efficiency
Many insulation manufacturers carry R-13 (medium density) and R-15 (high density) f.g., and stopped with R-11 (low density) because of meeting minimum building codes. FYI- R-13 has 40% more material than R-11, and R-15 has 180% more material than R-11, quite a bit more density-- with no inherent convective loops; The "biggest Loser" In Fiberglass Insulation.... - How To Guides - DIY Chatroom - DIY Home Improvement Forum

Using f.g. next to a window is a little better than leaving it empty, use foam: Airflow Performance of Building Envelopes, Components, and Systems - Google Books

Gary

 
Search this Thread