# Is moisture resistant drywall worth it?



## Bud9051 (Nov 11, 2015)

Finishing the walls in a basement, choice between the two, is the least of the concerns. Virtually ALL basements have to deal with moisture issues from liquid water to moisture vapor, the latter being always present and invisible. When you build a wall in front of the foundation that moisture vapor can accumulate and form liquid water and then mold.

So, before you choose your drywall, what have you done to manage any moisture?

Bud


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## LVDIY (Mar 28, 2011)

Basement walls are finished with 2" XPS with a framed wall in front.

I don't want to sidetrack the thread too much as there are plenty of discussions about the general topic of moisture control.

I have passed my framing and insulation inspection so I am at the stage where I am making the choice between the two.

Do you have anything to add on the merits of moisture resistant drywall?


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## Bud9051 (Nov 11, 2015)

Not drifting, the history is necessary as some posters might expect the moisture resistant drywall to be a solution to a serious problem, not. The little I have used had no paper on either side and for that reason only it would not be a bad choice. Looking at the purple paper you are asking about it looks like they are offering an improved product and just from what I can read (I'm sure you read as well) it is probably worth the extra. It is not like you can go back and change it easily so using it now it will be done.

I hate that basement smell as many people do. Good insurance.

Bud


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## rjniles (Feb 5, 2007)

I would use paperless drywall. Uses a fiber glass mat instead of paper.


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## bjbatlanta (Jul 16, 2008)

The only time I use it is if a customer insists.....


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## Gymschu (Dec 12, 2010)

I'm a painter who installs drywall on occasion when a homeowner can't contract a drywaller to do the job. I've never used moisture resistant drywall except back in the day when green board was the "go to" for bathrooms. I used regular drywall in my damp basement and I used a quality vapor barrier and I've had no issues to speak of. I've even removed some of the drywall at times to add a closet or reconfigure a room, and no signs of mold were ever seen on the backside of the drywall.


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## LVDIY (Mar 28, 2011)

Thanks everyone. I'm just about to start the ceiling and will go regular for that. I might do moisture resistant for the perimeter walls since it cant hurt, but not sure...

I'm still fuzzy on how big the actual difference is though, is it mainly marketing and a fancy purple color, or does it hold up significantly better in humid conditions?


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## Bud9051 (Nov 11, 2015)

My guess is, a little of both. But "humid conditions" is something you need to eliminate. Pick up a meter to read both temperature and humidity and refresh yourself on the fine points of dew point. Then make sure your basement temp/humidity remain well above that dew point. In many cases that will require a dehumidifier. But too much humidity will put many items in the basement at risk of mold. 

If I read it correctly the treated paper is actually just the back side of the drywall.

Bud


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## Gary in WA (Mar 11, 2009)

Not worth the extra money, IMHO. Do you really want some chemically treated paper on both sides of your drywall- just under the layer of texture/paint... Regular (paper faced) drywall has a perm rating of around 50, Purple at 37 perms- with the moisture resistant core- more chemicals; https://www.nationalgypsum.com/File/09%2029%2000-69.pdf

Paper-less at around 10 Perms so the wood studs stay wet for a longer time before the HVAC system removes it. Using Philly as your location, with 3 coldest months average temps of 35.5*F, and 2" FB (R-10) with R-13 cavity fill, 68*F in basement; good to 54% Relative Humidity and below- before it condenses on inside face (50*F) of FB. Above that, you'll need to dehumidify. A lot of test results show you don't want poly next to drywall in a basement. http://www.usclimatedata.com/climate/pennsylvania/united-states/3208

Gary


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## LVDIY (Mar 28, 2011)

Gary in WA, you bring up a very interesting point. If I understand you correctly, what you are saying is that the moisture resistant board with its lower perm rating will actually slow down the drying of any moisture between the board and xps layer?

So while the board itself might stand up to moisture better, it will actually to a larger degree trap moisture in the wall?

I think that makes me lean towards just going with regular board all around.

And I never planned on using any poly...


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## Bud9051 (Nov 11, 2015)

Hi LV, use either the purple or the paperless drywall. A vapor permeance of 10 is virtually vapor open. Your paint will probably have a lower permeance. The 2" of rigid foam board is your vapor retarder at something less than 1 so any moisture that gets past that (which will occur very slowly) will be able to dry to the inside easily.

As for chemicals, I doubt that the gold bond product represents any concerns, it would be only one of hundreds of products in our homes that would have to go. Going chemically free is a whole other issue.

Bud


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## LVDIY (Mar 28, 2011)

Hi Bud, so no practical difference between perm rating of 10 or 50, so I shouldn't let that be a factor in deciding?

By paperless, are you talking about products like densarmor? It seems like its about double the cost of regular drywall, but none of the big boxes around here carries it...


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## rjniles (Feb 5, 2007)

Densarmor is Georgia Pacific's brand. Any good lumber yard would order it. 

Sent from my RCT6203W46 using Tapatalk


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## Gary in WA (Mar 11, 2009)

I remember reading that when using Kraft-faced FG in a basement wall with 2" of XPS, the test results showed the Kraft facing starting to mold, due to its low permanence- wet cup limit around 10 perms; https://buildingscience.com/documents/insights/bsi-060-joe-south-assemblies. That is the link showing only the perms of faced, not the one I am still trying to find- reading through all my test results papers collected over the years. So with a *10 perm* drywall (OR Kraft-faced paper facing), look on the *chart of Fig. 3* there and notice the RH handled by a 50 perm drywall, or even your 37 perm one... *"diffusion and permeability"* on pp. 7; https://buildingscience.com/sites/default/files/migrate/pdf/BA-0202_Basement_Insulation.pdf

IMO, you want the drywall as open as possible because it is between the paint (3-10 perms) and your FB (0.76 perms), you don't want more lower perm materials on the inside to keep moisture in the cavity, on the studs longer. More open materials (higher perms) reduce the time and is better because the *temperature drive* -as per link-is not great enough (68*F room--- 50*F inside face FB) nor is the *pressure difference* (between cavity/room) enough to drive the moisture through the wall quickly because it is below grade- protected from winds/lower temps- as would it be above-grade with a greater drive. So, yes it is over 1 perm, not a vapor barrier- but how do they compare... I'd want 50 perm drywall, but it may not be as important to others. I am still looking for that link...

Gary


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## Gary in WA (Mar 11, 2009)

Another thought; with regular drywall (50 perms) you are helping move the moisture (RH) in the cavity out easier/sooner, so it won't permeate the wood studs- that have 1000 times the moisture storage capacity of the air in that stud bay. ADA the drywall or whatever you use as your air barrier, use foil faced (if no perimeter slab insulation or VB) FB under the bottom plate- check local AHJ for non-treated or at least use a sill sealer for the air/thermal/capillary break; http://www.greenbuildingadvisor.com...ressure-treated-sill-plates-and-building-code 

Gary


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## LVDIY (Mar 28, 2011)

Gary, thanks for another detailed answer. I just started drywall this weekend and so far the ceiling is getting regular drywall.

I still have the option of going moisture resistant on the walls, but I don't really see a clear benefit of doing so. Paperless is out of the picture with its low perm rating.


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