Kraft paper air sealing

[bluedog225]

Bottom line, I’m thinking seriously about heavy kraft paper on the interior walls as an air barrier. I can work with this stuff all day long. Tape holes, repair, whatever. Cheap, effective, breaths (slowly), no worries. And did I mention cheap?

Does anyone think I’m making a significant mistake? Or should I spend the money on the fancy stuff?

Details:

Cimate zone 2. Warm and humid.

I need to air seal my interior walls. And with air sealing, I’ll keep a lot of moisture out.

And I need the walls to be able to dry to the interior. There will be no water or moisture in getting in or out through the outside wall. Therefore, no moisture barriers on the inside.

I’m old fashioned and happy with it. And I’ll give up some efficiency for peace of mind. Towards that, I’m not going to spray foam. The fire risk, the performance over time, trapping moisture…no thanks. Maybe I’m wrong and that’s ok.

I am on the fence about fancy membrane products like Siga, Eco-air, Certainteed Membrain, etc.

Construction is as follows:

-metal siding (well sealed)
-1x4 treated spacers/rain screen (covered with tar paper to protect metal from treated wood)
-3/4 foil faced polyiso taped at seams with metal tape
-tyvek layer taped at seams
-3/4 CDX ply
-2x6 and 2x8 stud walls
-Mooney wall (horizontal 1x4’s) on the studs https://www.builditsolar.com/Projects/Conservation/MooneyWall/MooneyWall.htm
-Studs filled with Rockwool batts and covered with Rockwool ”boards” between the 1x4s.
-kraft paper
-Sheetrock or wood interior finish

Any speculation appreciated.

Thanks

 

[walta]

The way I see it you need one affective air barrier in your wall and its location in the wall is irrelevant.

I say concentrate your efforts and make the Tyvek layer be air tight.

Walta

 

[NUTTSGT]

Does the Kraft paper go over the 1x4's or go on before them ?

 

[bluedog225]

This wall is built but unfinished to the interior.

I was going to put the kraft paper on the interior surface. On top of the 1x4s.

With the idea that it will retard interior moisture going into the wall and air seal the wall. While at the same time, letting the wall dry to the interior.

I was looking at the journal of light construction and building science corp info here.

Seems to me that the kraft paper would serve well to keep air infiltration to a minimum.

All my utilities (water, gas, and electric will be surface mounted).

https://www.jlconline.com/how-to/insulation/understanding-smart-vapor-retarders_o

 

[mike93lx]

Taped poly iso, plus taped tyvek, plus kraft paper?

Belt, suspenders, and?

 

[bluedog225]

Yeah. The outside layers are done pretty well. Not letting moisture in, or out, that way.

I thought keeping the interior moisture out of the wall was important to prevent condensation forming inside the wall during our relatively brief cold season.

 

[billconner]

It's the asphalt on craft paper that makes it an air and vapor barrier. I believe that is what that article is referring to.

I'm a little surprised you want this on the inside in climate zone 2A. It's usually the exterior air that is moist and the condensation problem is when that moist air strikes a cold I side surface like the craft paper with asphalt, and condensed.

Your interior Sheetrock is a fine air barrier and will allow moisture to dry inwardly, like the BSC diagram you post.

 

[bluedog225]

It's the asphalt on craft paper that makes it an air and vapor barrier. I believe that is what that article is referring to.

I'm a little surprised you want this on the inside in climate zone 2A. It's usually the exterior air that is moist and the condensation problem is when that moist air strikes a cold I side surface like the craft paper with asphalt, and condensed.

Your interior Sheetrock is a fine air barrier and will allow moisture to dry inwardly, like the BSC diagram you post.

Do you think they’re referring to something I would call tarpaper?

 

[KenC]

Do you think they’re referring to something I would call tarpaper?

More likely they are referring to some brands of fiberglass batts that use kraft with a very thin coat of asphalt on the batt side.

I've read in a number of places over the years that a good latex paint is a very effect vapor barrier, that over the properly applied and finished wallboard (sheetrock) should suffice for both air and vapor. IMHO

 

[bluedog225]

Thanks. I agree with you on the sheet rock with latex paint. I’m on the fence as to whether or not I use nickel gap or shiplap siding running vertically up the walls. That’s one of the reasons I was looking into some type of air sealing.

 

[billconner]

I agree with KenC on the craft paper.
The nickel gap or t&g over the rockwool is a challenge. Based on my believing you're in a primarily cooling climate, I think trying to get exterior side as tight as possible and just installing the nickel gap over the rockwool is best bet. The wall will dry well inward. I'm more a climate zone 6 guy, so not sure, but wonder if Tyvek on inside might be a good air barrier and not inhibit drying.

 

[bluedog225]

I agree with KenC on the craft paper.
The nickel gap or t&g over the rockwool is a challenge. Based on my believing you're in a primarily cooling climate, I think trying to get exterior side as tight as possible and just installing the nickel gap over the rockwool is best bet. The wall will dry well inward. I'm more a climate zone 6 guy, so not sure, but wonder if Tyvek on inside might be a good air barrier and not inhibit drying.

I’ve had that very thought. It’s got a high permeability to vapor and would air seal the wall. The perm is so high you can double layer it without issue per the manufacturer.

Though I’ve not found anyone who agrees with me. I think it’s just because it seems weird.

 

[BillK]

Have you already done the insulation ? I would do fiberglass with kraft paper attached. I am pretty sure that is what they are referring to in your article above. Thats what I did in my attached garage.

 

[Hank11]

If the outside is air and moisture resistant, I think you are done. There‘s nothing to gain by putting paper inside.

 

[bluedog225]

Have you already done the insulation ? I would do fiberglass with kraft paper attached. I am pretty sure that is what they are referring to in your article above. Thats what I did in my attached garage.

I have not insulated much of it yet. But I‘ve gotten few bales of mineral wool batts. Pretty pleased with the stuff.

 

[Wiz02]

I agree with KenC on the craft paper.
The nickel gap or t&g over the rockwool is a challenge. Based on my believing you're in a primarily cooling climate, I think trying to get exterior side as tight as possible and just installing the nickel gap over the rockwool is best bet. The wall will dry well inward. I'm more a climate zone 6 guy, so not sure, but wonder if Tyvek on inside might be a good air barrier and not inhibit drying.

Can you explain "nickel gap" over the rockwool? While my application is stick built 2×6 walls, scissor trusses for the roof, with exterior tyvek covered with vinyl siding. I am planning on using rockwool and can't decide if I should apply anything over the rockwool before covering it with sheetrock.

According to: https://basc.pnnl.gov/building-assemblies/climate-zone-lookup

I am in climate zone 4a

 

[mike93lx]

Can you explain "nickel gap" over the rockwool? While my application is stick built 2×6 walls, scissor trusses for the roof, with exterior tyvek covered with vinyl siding. I am planning on using rockwool and can't decide if I should apply anything over the rockwool before covering it with sheetrock.

According to: https://basc.pnnl.gov/building-assemblies/climate-zone-lookup

I am in climate zone 4a

Nickel Gap vs. Shiplap: Key Differences, Costs & Which to Choose (2026

The Short Answer Both nickel gap and shiplap create that horizontal plank wall look—but they’re built differently, installed differently, and look distinctly different once they’re up. The short version: shiplap uses overlapping boards with a rabbet joint, giving you flexibility in gap width and...

www.stikwood.com

 

[Wiz02]

Nickel Gap vs. Shiplap: Key Differences, Costs & Which to Choose (2026

The Short Answer Both nickel gap and shiplap create that horizontal plank wall look—but they’re built differently, installed differently, and look distinctly different once they’re up. The short version: shiplap uses overlapping boards with a rabbet joint, giving you flexibility in gap width and...

www.stikwood.com

Thanks, not doing anything fancy like those products, plain old sheetrock for my garage.

 

[nmk_61802]

My Opinion.... You already have a good vapor barrier on the outside with the foil faced insulation. You should not be doubling up any vapor barrier, any moisture that passes will need somewhere to dry too. I would guess your temperature zone would need the vapor barrier to the outside (as you have it already). If you want to further air seal the wall concentrate on foaming/ caulking/ taping anything to the outside barrier.

Rockwool also doesn't hold water like fiberglass, so it is less of a worry if some moisture infiltrates, as long as it can dry to some direction.

Edit to add that Tyvek/ Typar or similar are also already affective exterior air barriers when installed correctly.

 

[Sumboodie]

More likely they are referring to some brands of fiberglass batts that use kraft with a very thin coat of asphalt on the batt side.

I've read in a number of places over the years that a good latex paint is a very effect vapor barrier, that over the properly applied and finished wallboard (sheetrock) should suffice for both air and vapor. IMHO

It's SOP here to do a plastic vapor barrier, usually ~10 mil thick, then the drywall.

 

[billconner]

It's SOP here to do a plastic vapor barrier, usually ~10 mil thick, then the drywall.

Sure, youre in Alaska. OP is in Texas.

 

[mike93lx]

Sure, youre in Alaska. OP is in Texas.

Another post acting as if everyone lives in Alaska's climate. It's almost like it's a running gag that it happens so much

 

[Sumboodie]

Sure, youre in Alaska. OP is in Texas.

Ok. It's not like I had any idea where he lives!

He said zone 2 which is same as here.

 

[racecougar]

Ok. It's not like I had any idea where he lives!

He said zone 2 which is same as here.

You do this in most every thread.

 

[billconner]

Ok. It's not like I had any idea where he lives!

He said zone 2 which is same as here.

Where in Alaska is it hot and humid for most of the year? According to the IRC, all of Alaska is on zone 7 or 8.

 

[Crazyjake8493]

You already have a vapor barrier on the outside with polyiso, foil tape, and tyvek.

You are correct that you want the wall to dry to the interior, since you are in a cooling climate.

You do NOT want another vapor barrier on the inside of the wall construction.

Caulk the penetrations around receptacle and switch boxes, and any other interior penetrations.

 

[Sumboodie]

Where in Alaska is it hot and humid for most of the year? According to the IRC, all of Alaska is on zone 7 or 8.

AK is mostly zone 2a, 2b, and 3, depending which part. Anyhow, not relevant to the thread.

 

[nmk_61802]

AK is mostly zone 2a, 2b, and 3, depending which part. Anyhow, not relevant to the thread.

I would say it’s somewhat relevant if you are saying OP’s climate zone is the same as Alaska’s. I think you may be confusing planting climate zones with insulation zones? RaceCougar posted a clear image of the insulation zones in post #24 that shows OP in the 2-4 range while Alaska is 7-8. If I look at the planting hardiness zones, I do see that Alaska is mostly 2-3, but I don’t know how you would correlate that to insulation.

 

[racecougar]

Yep. That is a completely different classification. The thread is discussing insulation, not plant hardiness.

 

[Sumboodie]

I would say it’s somewhat relevant if you are saying OP’s climate zone is the same as Alaska’s. I think you may be confusing planting climate zones with insulation zones? RaceCougar posted a clear image of the insulation zones in post #24 that shows OP in the 2-4 range while Alaska is 7-8. If I look at the planting hardiness zones, I do see that Alaska is mostly 2-3, but I don’t know how you would correlate that to insulation.

Not seeing any photos.

 

[racecougar]

Not seeing any photos.

You don't see images in posts #24, 25, and 29?