# Drywall screws for pressure treated lumber?



## jbrah (May 29, 2018)

I noticed on the box of phosphate coated drywall screws (black bugle head screws) that these are not for use in PT lumber. Well, my bottom plate is PT. And I'm guessing the copper in today's PT lumber will destroy these screws in a matter of months.

What screws should I use to secure the drywall here? Deck screws?


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## huesmann (Aug 18, 2011)

Simpson says to use hot dipped galvanized, or Types 304, 305 and 316 stainless. I'd think they would know.


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## Windows on Wash (Aug 30, 2011)

+1. Drywall screws are intended for interior application and not to be exposed to moisture or the preservatives in PT. Use a coated screw for deck applications or the specified fastener by Simpson.


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## mark sr (Jun 13, 2017)

Assuming you mean the PT bottom plate used on slab construction - I wouldn't worry about it too much as the base will also cover that part of the drywall. If I did anything, I'd use roofing nails where the drywall attaches to the PT plate.


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## joecaption (Nov 30, 2011)

Roofing nails would also just corrode.
Like wow I also just use ceramic coated deck screws since I already have them on hand and there ACQ approved.


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## Bud9051 (Nov 11, 2015)

That drywall could be in place for 40+ years, use screws rated for the job. Stainless steel screws would be my choice unless I was buying a lot and then maybe the hot dipped galvanized. 

Bud


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## Spyder (Jan 11, 2019)

just screw into the studs. if you "need' to, put 1 in the bottom plate and 1 just above it into regular lumber.

isn't screwing along the bottom plate gratuitous anyway?

Id feel differently if the whole wall was PT (it shouldn't be)


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## jeffnc (Apr 1, 2011)

Yeah, I don't understand the need to screw into the bottom plate to begin with.


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## Nealtw (Jun 22, 2017)

joecaption said:


> Roofing nails would also just corrode.
> Like wow I also just use ceramic coated deck screws since I already have them on hand and there ACQ approved.


Read Joe's post again.


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## Yodaman (Mar 9, 2015)

It just ties the wall studs to the base a little better. But I like to put a screw in the base directly under the studs. It makes it easy to find the studs when it comes time for base molding.


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## ron45 (Feb 25, 2014)

With the amount of screws used, placement, along with the baseboard, I have never seen a problem using regular drywall screws.


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## ZZZZZ (Oct 1, 2014)

Yodaman said:


> It just ties the wall studs to the base a little better. But I like to put a screw in the base directly under the studs. It makes it easy to find the studs when it comes time for base molding.


Great tip, Yoda. Never thought of that.

Just don't air nail into the screw. :biggrin2:
.
.


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## jeffnc (Apr 1, 2011)

Well, another thing to take into account is that drywall is supposed to be installed from the top down. Install ceiling drywall first, then install the walls at the top so they're pressed against the ceiling to help support it, and form a tight joint that is stronger when that corner is taped. Then the bottom piece of drywall (we're talking about standard installation of 4x8 drywall installed horizontally with 8' ceilings) is pressed up against the top piece using a drywall foot lifter. Often times, this does not even allow enough room on the bottom plate to screw into without damaging the drywall anyway. USG acknowledges this in their installation instructions: "A filler strip may be needed". So while theoretically it might be true that attaching the drywall to the bottom plate "ties" the studs to the plate to a very small degree, drywall is by no means a structural element, and in fact this might not even be desirable because if there is any shrinkage, warpage or twisting, it is more easily going to be transferred to the drywall and potentially cause some cracking. This especially true considering pressured treated lumber is wet. So I wouldn't want any drywall connected to it at all, myself.


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## ron45 (Feb 25, 2014)

ZZZZZ said:


> Great tip, Yoda. Never thought of that.
> 
> Just don't air nail into the screw. :biggrin2:
> .
> .


Most mark the floor where the studs are.


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## Old Thomas (Nov 28, 2019)

Glue to the treated lumber.


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## jeffnc (Apr 1, 2011)

Old Thomas said:


> Glue to the treated lumber.



Why? Drywall doesn't need to be attached to the bottom plate.


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## Old Thomas (Nov 28, 2019)

Agreed that it can be left unattached at the bottom. The poster asked about attachment, so if that is what he wants glue will accomplish it.


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## jeffnc (Apr 1, 2011)

Old Thomas said:


> The poster asked about attachment



Well if you want to get technical, he didn't ask that, he asked what screws he should use  Not trying to pick on you, but I'm saying after all the discussion in this thread, hopefully it's clear by now to the OP that he's asking the wrong question, because he doesn't need anything to attach it. This is one long red herring conversation. If someone else comes along and says it can be attached with stainless steel nails, I'll say the same thing - why? Or if someone else says replace the bottom plate with a regular 2x4 and protect it from the concrete with plastic, again I'll say why? Why are we still talking about this? This would only be a question if the vertical studs were pressure treated.


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## jbrah (May 29, 2018)

jeffnc said:


> hopefully it's clear by now to the OP that he's asking the wrong question, because he doesn't need anything to attach it.


OP here, and I should have provided more color in the initial post.

The reason I was asking about screwing into the PT bottom plate is I'm looking to get an airtight drywall setup. Backing up one step, I'll be attaching 1/2" foam board to the room-interior-facing-edges of studs and bottom/top plates to mitigate the thermal bridging effect. Then drywall on top of that.

So I was thinking I'd apply polyurethane construction adhesive to the foam board strips where the perimeter of each piece of drywall will attach. Then screw in the drywall (using 2" screws). I was thinking that screwing in along the bottom plate would help seal the bottom edge of the drywall by ensuring firm contact with the adhesive on the foam board while the adhesive cures.

If the drywall will be pressing firmly against the foam board and adhesive along the bottom plate just from driving in a screw 1" up from the bottom of each stud, then I can skip the screws into the bottom plate.


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## jeffnc (Apr 1, 2011)

jbrah said:


> The reason I was asking about screwing into the PT bottom plate is I'm looking to get an airtight drywall setup. Backing up one step, I'll be attaching 1/2" foam board to the room-interior-facing-edges of studs and bottom/top plates to mitigate the thermal bridging effect.



There's a bid difference between airtight and thermal bridging. Drywall on wood studs does not really present a thermal bridge.


Check out the section "Reduced effectiveness of insulation" particularly.



*https://www.kore-system.com/blog_list/thermal-bridging-what-it-is-why-you-should-avoid-it/
*


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## ZZZZZ (Oct 1, 2014)

ron45 said:


> Most mark the floor where the studs are.


I've done that, but by the time all the rest of the construction, painting, lots of sweeping up etc are done, the marks on the floor are gone. :biggrin2:
.
.


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## Yodaman (Mar 9, 2015)

ZZZZZ said:


> I've done that, but by the time all the rest of the construction, painting, lots of sweeping up etc are done, the marks on the floor are gone. :biggrin2:
> .
> .



And they are definitely gone if you have just put down your finished floor and are looking for studs to nail your base mold to.


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## jbrah (May 29, 2018)

jeffnc said:


> There's a bid difference between airtight and thermal bridging. Drywall on wood studs does not really present a thermal bridge.
> 
> 
> Check out the section "Reduced effectiveness of insulation" particularly.
> ...


Jeff, I don't follow. I'm not saying airtight drywall and thermal bridging are the same.

The wood studs are a thermal bridge. I lined the stud bays with 1/2" foam. Using a heat gun, I just checked the surface temp of the foam - it's 56*F. The surface temp of the stud face next to it is 53.3*F. Once the cavity is filled with insulation, the differential will be even greater - i.e., the studs are acting as thermal bridges.

So the idea is foam strips covering the stud faces (and also bringing the cavities back to 3.5" depth so I can fit standard insulation without compressing it). Then getting an airtight seal between the drywall and the foam, so there's no free flow of interior air into the wall cavities.


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## Yodaman (Mar 9, 2015)

Have you considered completely sheathing over the studs with foam board and taping the seams? This will reduce the thermal bridge, provide a air barrier, and increase the insulation value of the wall.
One inch of high density foam will add about R5.

Compressing 1/2" of fiberglass is not a big deal. Then of course drywall over.

This would also allow you to use un-faced insulation. Although I doubt it would save you any money, un-faced does install a little quicker.


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## jbrah (May 29, 2018)

Yodaman said:


> Have you considered completely sheathing over the studs with foam board and taping the seams? This will reduce the thermal bridge, provide a air barrier, and increase the insulation value of the wall.
> One inch of high density foam will add about R5.
> 
> Compressing 1/2" of fiberglass is not a big deal. Then of course drywall over.
> ...


Everything I've seen on insulation says not to compress the batts, so I figured it would be safest to cut foam board strips to cover the studs and get back to 3-1/2" depth cavities. Also, since the back of the cavities are now air sealed (1/2" foam board with spray foam around perimeter), I was thinking foam board sheets over the framing would create a foam sandwich that would trap any moisture that gets inside the cavities (no path to drying to the exterior or interior). 

I suppose the moisture trapping issue could be mitigated by removing the facing from the foam board sheets? The facing peels off fairly easily from the FOAMULAR 1/2 in. x 4 ft. x 8 ft. R-3 Square Edge Rigid Foam Board Insulation Sheathing.

As for the insulation compression issue, I was planning on using Rockwool. Would compressing that from 3-1/2" to 3" have a material reduction in insulating value?

The benefit of your suggested approach vs cutting foam board strips to cover only the studs, in addition to further air sealing and greater overall insulation value of the wall (assuming it's not negated by compressing Rockwool from 3-1/2" to 3"), is saving time/effort. It's a lot easier to put up entire sheets than cutting foam board into narrow strips.


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## Yodaman (Mar 9, 2015)

In theory you would loose a little R value by compressing. Theory being compressed fiberglass is no greater R factor than loose. So a R15 mat'l made for 3.5 cavity provides 4.29 R per inch. So the same insulation put into a 3" cavity should theoretically yield R12.8. Of course that is in a perfect world in lab conditions. But on the other hand insulation that is too loose, or doesn't fill the cavity completely is just a harmful. Loose insulation can leaves voids. And voids collect cool air that can cool surfaces.

1/2" ? I wouldn't be concerned about it. When you remove it from the pkg it's already squashed to about 1-2" thick. 

Since you are air sealed at the the back of the cavity with a closed cell product, best to leave it as is. Pealing the foil would still not guarantee permeability. 

Another option might be to use open cell un-faced foam board on the inside. It should not trap vapor. It would help with the bridging issue, and provide some additional R value.


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## jbrah (May 29, 2018)

Yodaman said:


> Since you are air sealed at the the back of the cavity with a closed cell product, best to leave it as is. Pealing the foil would still not guarantee permeability.
> 
> Another option might be to use open cell un-faced foam board on the inside. It should not trap vapor. It would help with the bridging issue, and provide some additional R value.


That's an interesting idea, but all the foam board I've seen is closed cell - XPS, EPS and polyiso.

I guess I'll stick with cutting strips of XPS foam to cover the stud and bottom/top plate faces. Turn on some podcasts and do a whole lot of foam cutting!

On a side note, air sealing the room has made a huge difference. Don't get me wrong, it's pretty cold in that room (no insulation, no drywall, no heat (disconnected the hydronic heat pipe in this room during the remodeling), but prior to air sealing, I could feel cold air blowing in. Now it's just cold, but without the draftiness. So I'm hopeful that with Rockwool insulation, insulating the studs, and a layer of drywall, this room will be fairly comfortable (it was by far the coldest/hottest room in winter/summer).

Before I put in the Rockwool, I'm going to go around with some incense and see if there are any remaining air leaks.


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## ron45 (Feb 25, 2014)

ZZZZZ said:


> I've done that, but by the time all the rest of the construction, painting, lots of sweeping up etc are done, the marks on the floor are gone. :biggrin2:
> .
> .


Scheduling is everything.


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