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grover
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# Posted: 22 Nov 2013 08:07
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I'm thinking about how I'm going to do my ceiling insulation. I have scissor trusses with an outside pitch of 12/12 and an inside pitch of 8/12. My thought now are to use the netting stapled on and blow in cellulose. Then tounge & groove or drywall.
Question is if you need a moisture barrier on the walls such at the paper on the roll insulation why no barrier on the ceiling? Or do I even need a moisture barrier on the walls
I live in the southern most portion of Indiana. Temps range from 0 in the winter to 100 in the summer.
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MtnDon
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# Posted: 22 Nov 2013 10:07 - Edited by: MtnDon
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Quoting: grover if you need a moisture barrier on the walls such at the paper on the roll insulation why no barrier on the ceiling? Or do I even need a moisture barrier on the walls
Who/what says you do not need a vapor barrier on the ceiling?
You are in climate zone 4. The only zones that do not need vapor barriers is 1, 2, 3.
But that said all you probably really need where you are is drywall with all seams and corners taped very well and a coat of good paint, as long as the space above the insulation is very well ventilated. The drywall will act as a good air movement barrier; T&G does not. If you want T&G place the T&G over well taped drywall.
There is usually much more leakage of air and the moisture it carries because of poor air sealing than by diffusion of water vapor through the actual wall/ceiling materials.
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grover
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# Posted: 22 Nov 2013 13:07
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Should I use housewrap under the t&g? Much easier than drywall.
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MtnDon
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# Posted: 22 Nov 2013 14:32
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My own experience with applying polyethylene plastic to the underside of a roof or ceiling has shown that to be a much more difficult task than I thought it would be. IF I was contemplating doing it again I would choose polyethylene over housewrap. Reason: then I would also have the vapor barrier as well as an air barrier; housewrap is not a vapor barrier. . Same amount of effort and maybe a better result. I say maybe because it is still hard to achieve a good seal all around.
YMMV
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bldginsp
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# Posted: 22 Nov 2013 16:26
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The reason a moisture barrier is frequently used on wall insulation is that the other side of the insulation in the wall is not ventilated. The general assumption with ceilings with attic spaces is that the attic above the insulation is vented to carry off moisture, so the barrier is not needed for that reason, but, as stated above, it works well to reduce air leakage that wastes heat.
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grover
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# Posted: 22 Nov 2013 16:55
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I read a little bit of an article titled "Air Barriers vs Vapor Barriers"on building science where it talks about the difference. I'm not sure that I understand all of the details or the difference. My interest is in sealing all the air infiltration that I can and have plenty of insulation "R" value in the attic. Other articles talk about, as you did, the drywall and taping being a barrier.
As of now I don't know if I will have drywall or wood on the ceiling. Money will dictate that at the time. If I'm understanding you correctly you are saying in my climate zone I need a air barrier of polyethylene between my T&G and my insulation. I think that's the same thing I'm using in my crawl space, which is basically plastic.
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MtnDon
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# Posted: 22 Nov 2013 17:27
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Quoting: grover If I'm understanding you correctly you are saying in my climate zone I need a air barrier of polyethylene between my T&G and my insulation.
Yes, and R38 in the ceiling. Taped drywall is a great air barrier. If the plan is to cover with T&G it does not need to be cosmetically perfect. Ours is pretty ratty looking where I knew it would be covered. The poly acts as a vapor barrier which is okay in your zone. If you were farther south in climate zone 3, 2, or 1 the poly would be a bad idea. You would want a vapor permeable air barrier further south.
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grover
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# Posted: 22 Nov 2013 23:43
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Should I drywall under my T&G? I hadn't planned on it. Also, Is't there a point where your cabin can get too airtight? Can't that cause a mold issue?
Thanks for your input Don.
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MtnDon
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# Posted: 23 Nov 2013 11:35 - Edited by: MtnDon
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Quoting: grover Also, Isn't there a point where your cabin can get too airtight?
That is possible, but probably not likely for most builders. Just my opinion. The ceiling/attic air seal has the potential for being the biggest loser because of the rising hot air effect. Air will pass through a poorly sealed ceiling before most other places. That is why I think it is important to do the best job possible on the ceiling air seal.
The next likely leaker is in the floor assembly. Also temperature driven especially with a raised floor.
You can balance what to do with the ceiling with the intended use of the cabin. The more likely it is to become used for extended periods the better the air seal should be, IMO. And as it is with many things it is a whole lot easier to do it "right" now than it is to come back later and try to improve it.
If you have a couple of helpers 6 mil polyethylene can be installed to do a pretty good job of air sealing. And of course the same thing can be said for having helpers and drywalling.
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grover
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# Posted: 24 Nov 2013 00:39
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Thanks for all your help.
So, in my area (zone 4) I should use 6 mil plastic on the ceiling and then at least R38 insulation on top of that? If I need plastic on the ceiling then do I need plastic on the inside of the walls if I am not using drywall on the walls?
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MtnDon
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# Posted: 24 Nov 2013 15:47
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Quoting: grover So, in my area (zone 4) I should use 6 mil plastic on the ceiling and then at least R38 insulation on top of that?
...and make sure the upper attic area is well vented. ridge vents and soffit vents are best with more soffit area than ridge area.
http://publicecodes.cyberregs.com/icod/irc/2012/icod_irc_2012_8_sec006.htm
Quoting: grover If I need plastic on the ceiling then do I need plastic on the inside of the walls if I am not using drywall on the walls?
Yes. If that would be the only vapor barrier... as in you do NOT have any rigid foam inside the wall cavities or applied to the exterior walls.
You, and anybody else, do NOT ever want to have two vapor barriers with some space encapsulated between them.
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rockies
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# Posted: 24 Nov 2013 18:21 - Edited by: rockies
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http://www.buildingscience.com/documents/digests/bsd-115-wood-pitched-roof-constructi on/?searchterm=scissor truss
This article describes several different types of roof construction. The section after the heading "figure 4" decribes the typical "cathedral ceiling" style (which is what yours basically is) and mentions that a "scissor truss" is a better method for building this type of roof since the truss allows more room in the attic space for better ventilation. There is a section drawing (figure 4) showing the layers needed for a vented cathedral ceiling, but a scissor truss is basically the same type of design (the interior angle is just lower than the outside roof pitch). There are more articles on the "building science" website (search in the information area) about vapour barriers and insulation techniques, as well as ventialation requirements for your climate zone
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grover
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# Posted: 8 Dec 2013 13:57
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MtnDon,
I was reading through building science and the way I read it I see "No interior vapor control required on the interior side of framed walls in climate zones 1, 2, 3, 4a, or 4b." I'm in 4a.
http://www.buildingscience.com/documents/information-sheets/info-sheet-310-vapor-cont rol-layer-recommendations/?searchterm=climate%20zone%20map
Now I'm really confused.
It also defines 3 classes of vapor control.
Class I . <0.1 perms e.g. polyethylene sheet, sheet metal, or aluminum facing.
Class II. 0.1 - 1.0 perms e.g., kraft faced fibreglass batts, and some vapor control paints.
Class III. 1.0 - 10 perms e.g. latex or enamel paints.
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MtnDon
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# Posted: 8 Dec 2013 16:11
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There's reason to be confused. Info changes. Look at the sidebar in the link you posted. BSD-106 is listed. It does not list any requirement for zone 4 needing a VB. But that article is older.  Things evolve. The good thing is likely you are in a place where you could go either way and be right. Use the latest info. Hope there's not anything newer that goes back to the old. Codes do not stand still and somewhere on BS I did read that VB and insulation is one of those evolving areas.
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grover
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# Posted: 8 Dec 2013 17:36 - Edited by: grover
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I'm not really sure how to process all the info especially the different classes of vapor barrier. I had always wondered how they could call the kraft faced fiberglass a vapor barrier. I guess it is just a different class of vapor barrier.
Follow up question...If I could afford the inch or so of closed cell foam on the back side of the OSB (inside the wall cavity) wouldn't that serve as a vapor barrier on the wrong side of the insulation, assuming I netted and blew in cellulose after the foam?
I think it comes down to me wanting to use T & G on the walls and not drywall. Without the drywall it seems I need some form of vapor barrier under the T & G. I think that is why in one our discussions in the past asked about house wrap under the T & G.
I'm thinking I may try to contact a home inspector in my area and see what they think.
Like everyone else I would like a tight, well insulated space and no worries about mold.
And MtnDon, thanks for sticking with me in this discussion. I will report back after I talk to the inspector.
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MtnDon
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# Posted: 8 Dec 2013 18:12
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Quoting: grover the inch or so of closed cell foam on the back side of the OSB (inside the wall cavity) wouldn't that serve as a vapor barrier on the wrong side
It's only on the wrong side if it is not thick enough, doesn't have a high enough R-value. When rigid sheet or spray on foam is used on the outside of some other vapor permeable insulation like cellulose or batts of f'glass or denim, IF it has a high enough R-value it is okay. With enough foam R-value on the outside, the inner face of the foam will be warm enough, it will be above the dew point. No moisture will condense on the inside face of the foam. The amount of foam needed varies with the amount of interior 'other' insulation. Varies with climate zone too.
What then happens is any moisture in the air dries to the inside. In winter it is normal to have low humidity inside. In summer if there is A/C the air also dries well to the inside.
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razmichael
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# Posted: 8 Dec 2013 18:14
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Quoting: grover .If I could afford the inch or so of closed cell foam on the back side of the OSB (inside the wall cavity) wouldn't that serve as a vapor barrier on the wrong side of the insulation, assuming I netted and blew in cellulose after the foam?
Often called "Flash and Batt". Google it to get more information. One example Flash and Batt - Green Building Site. Note the requirement to use closed cell foam (higher R value but more expensive) the need to calculate the depth needed to ensure the dew point remains within the foam. You do not use a second vapor barrier! I think this is becoming a more popular technique due to the cost savings. Some like it and some do not. Pros and Cons as you would expect.
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toyota_mdt_tech
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# Posted: 8 Dec 2013 21:52 - Edited by: toyota_mdt_tech
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Vapor barrier on the inside is easy if you know a nice little trick. My son in law deals with hazardous material (asbestos, vermeculite, mold etc) removal and he will re insulate. He brought me some semi clear 6 mil plastic. He used a commercial type duct tape, it was black in color. I think it was called Tuff Tape and its the best tape I have found. He would take this tape and run out a strip about 2 feet long on a piece of wood, then a 2nd and 3rd layer. Then he would take a razor knife and cut it into 1" squares (diced it up) and so he ended up with a bunch of 1" square pieces of duct tape, 3 layers thick. Then stuck these squares to his coveralls. He would start setting it up from the top. Take a piece of his square chunks of tape from his chest, stick in on the area to be stapled. Then put 3 staples through the tape and plastic, did this all the way across the top pulling it drum tight as he went along. The staples do not pull through. Then he would work his way downward, attaching it to the studs all while pulling it tight. Then across the bottom. We did this to all my walls and ceilings, then the same tape, we used to seal all the corners. It was basically air tight. The plastic was all drum tight.
Here is a picture of it, go to:
http://www.small-cabin.com/forum/6_431_0.html#msg23413
Then down to the 6th post.
I was worried it would be too air tight. But I suspect it breathes well enough. The air over there is real dry, little moisture. 300+ days of sunshine, warm in the summer, real cool in the winter but dry
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Sambo
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# Posted: 8 Dec 2013 22:33
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What's the r-19 paper holding up against the bats called? I've never seen that before.
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grover
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# Posted: 8 Dec 2013 23:14 - Edited by: grover
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That's just faced insulation. I've heard it called kraft paper faced.
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BuckyBadger
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# Posted: 9 Dec 2013 18:21 - Edited by: BuckyBadger
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toyota_mdt_tech.....So it's ok to have 2 vapor barriers?
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grover
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# Posted: 9 Dec 2013 21:09
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I talked to a local building inspector. I would expect him to be up on the local practices and he said he would not do a class I vapor barrier in our area. I plan on calling a spray on foam company and see what kind of money I will be looking at for a "flash and fill" wall system. At the very least I will get a bunch of caulk and seal all around each wall cavity where the OSB meets the 2x4's and at the bottom plate/floor, can foam where my exterior outlets are and then net and fill the cavity with cellulose.
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toyota_mdt_tech
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# Posted: 9 Dec 2013 21:57 - Edited by: toyota_mdt_tech
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Quoting: BuckyBadger toyota_mdt_tech.....So it's ok to have 2 vapor barriers?
Is that paper considered a vapor barrier? Or just used to attached the insulation to the studs with the stapler flanges? Paper is breathable.
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MtnDon
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# Posted: 9 Dec 2013 22:07 - Edited by: MtnDon
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If you can stop any air exchange you will be way ahead of the game. Will the cellulose be dense pack? Performs well and also helps greatly with air infiltration.
Quoting: BuckyBadger So it's ok to have 2 vapor barriers?
It would probably be best if the kraft was slashed before the poly was installed. Partly depends on how well the exterior sheathing was air sealed.
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grover
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# Posted: 10 Dec 2013 22:52
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I see my challenge being stopping air exchange without totally restricting vapor movement. In my area it seems this is usually done with 1/2 inch drywall. I would really like to limit the use of drywall in favor of tongue and groove pine if at all possible. So it's either put up drywall, tape the seams, and put T & G over that or find an acceptable substitute for the drywall. Is there a foam board 1/4 inch or 1/2 inch that would be an acceptable substitute? Is there one that would not totally restrict vapor movement?
Another thought I had while thinking about the paper used on fiberglass roll insulation. I know you can buy rolls of kraft paper. Has anyone used these rolls for this purpose? Bascally just stapled up and taped before the T & G goes up? That may be a stupid idea but I thought I'd throw it out there.
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MtnDon
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# Posted: 11 Dec 2013 14:25
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Seems to me there is a difference between the kraft used on f'-glass batts and the wrapping paper type. The type used to face f-glass batts has a thin coating of asphalt or tar on the side that faces the f-glass. That is what makes it a vapor retarder.
I personally don't like the idea of hanging T&G over a thin layer of foam without furring strips over the foam. Good rigid foams are not permeable. The foams that are not water resistant are softer and IMO that could lead to some issues of being "squished" when the T&G is nailed. Not certain, but it gives me concern unless there were furring strips over the foam to nail to. And that doesn't make a lot of sense to me when drywall is perfect for the task. It doesn't need to be made as pretty as if the drywall was the final finish.
One other reason I do not like the thought of foam on the inside of the studs is what happens when fire hits foam.
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creeky
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# Posted: 11 Dec 2013 16:26
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the link that Rockies put up ... building science ... need i say more, but
my take would be:
a) your biggest concern is the summer cooling season. so look at venting of the roof. ridge vents, ahem.
b) you probably are overly concerned with the vapour barrier issue. buildings that breath are good buildings.
i like your idea of putting up a foam based board insulation and then putting the t&g overtop. just know that foam boards are vapour barriers. so make sure that the foam layer. on the outside or the inside of the building. is the only vapour barrier.
there is no way that the pressure of the installed t&g will affect the xps or polyiso foam.
of course I would recommend using polyiso. xps is okay too. the tin foil wrapped polyiso has some really good attributes (fire prevention/not explosively flammable). again. source building science and mfc websites to learn more.
there is nothing wrong with a 1/2" of drywall. but if you're using t&g you do not need drywall. why spend the time and money?
personally i am a big fan of Roxul batts between joists combined with a polyiso insulation layer. but i live in a colder climate. see point a.
also. if you're going to use kraft paper. look at the waxed paper underlay you can find for flooring. man it's cheap. 
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MtnDon
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# Posted: 11 Dec 2013 22:19 - Edited by: MtnDon
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grover, IIRC, you have stated a few times here and there that you want this project to be well built, efficient and long lived. If you have not used those words that is the impression I have. It's not just a cabin as some folks here have referred to their projects, but something want to enjoy for years, maybe pass on to the next and future generations.
You have also stated that money is a concern. Of course it is, there is no one here who has unlimited funds. However, I strongly believe that it is foolish to cut corners in areas that are basic to a long lived structure. Shortcuts in basics almost always lead to remedial work down the road and that will definitely cost more than doing it the best way right now. There are places where money can be saved now, and improvements made at a later date when the budget permits.
For example, I know people who have lived with painted plywood floors in their full time residence until (10 years later) they could afford to do the hardwood they wanted. But they installed high quality windows in the basic building stage and reaped the benefits from them all that time. My wife and I built our home and did a full drywall only interior. We had plans for nicer walls in some areas and a vaulted ceiling with wood planking. I said plans, I should have said dreams... the budget did not allow for real wood and stone. Over the years (15 of them) we have upgraded one wall with cut stone, another with ceramic tile and vertical T&G and the vaulted ceiling with fake beams and rough cut red cedar planks. (planks that are really only 3/8" boards.) All of our floors have been redone from the original cheap wall to wall carpet to ceramic tile everywhere save the bedroom that is hardwood. We finally got what we wanted 15 to 20 years after we started out. The basic box we started with is solid; we just took our time fancying it up to more or less what we envisioned back in the mid 80's.
My point is the most important part of doing a good wall and ceiling is to have a great air movement barrier. I know of two DIY builders right now who are trying to remedy air infiltration problems that make their cabins cold. They did not, IMO, take sufficient time and proper care to that sort of detailing. Yes we do need some air changes, fresh air to be introduced inside. Very few of us are ever going to have things so tight that that becomes a worry. I've seen blower door tests performed and everyone except the guys doing the testing are surprised at the amount of air leakage.
If you have built the roof assembly with good soffit and ridge ventilation you owe it to yourself to make the best air infiltration barrier between the living space and that vented attic / roof truss space. The attic / roof venting can be so good it can act to suck air through your T&G ceiling. T&G looks great but it is almost as air leaky as window screening. Do yourself a long term favor and drywall anything that is on an exterior surface; walls, roof.
If you don't listen to anybody else go by the building science guys. Take their word over anyone else's , especially any claims made on websites that promote any particular products. It would be difficult to go wrong with the methods of buildingscience.com properly executed.
Of course if this project is to be "just a cabin" forget anything I suggest.
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MtnDon
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# Posted: 11 Dec 2013 22:37 - Edited by: MtnDon
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A Joe Lstiburek, of Building Science, quote:
"A vented attic, where insulation is placed on an air-sealed attic floor, is one of the most underappreciated building assemblies that we have in the history of building science."
~~~~~~~~~
and a quote from a greenbuildingadvisor article.... (True this is aimed at a true cathedral ceiling, but the scissors truss ceiling is a close relative...)
"If you are building a cathedral ceiling, the biggest air-barrier blunder is to install tongue-and-groove boards as your finish ceiling without first installing taped gypsum drywall. A board ceiling is notoriously leaky..."
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grover
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# Posted: 12 Dec 2013 07:52 - Edited by: grover
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I feel like the dead horse that is still being beaten No offense Don I know you are trying to help.
It seems a real waste of energy to put up drywall just for the barrier it provides and then put something over the top of it. I could understand if for money reasons you put up drywall with the intent of going over it in the future with the T & G. Or if you are doing a remodel and put T & G over drywall at that point.
Drywall is such a pain to put up (heavy & bulky) especially on a tall ceiling like I have. I may end up using it anyway because I haven't priced out the T & G.$$$ Then again it more than likey will end up being a combination of the two.
Creeky, believe me I have been reading building science. I just haven't seen a specific artical that addresses T & G on interior walls and/or ceilings but I'm still reading.
If that drywall is the answer I will use it, I just won't like it.
Thanks all
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