Running Pex through metal frames in basement - vapor barrier?

[Mgmny]

Hello!

I just finished framing out my unfinished basement with galvanized steel studs. I am now going to turn to electrical and plumbing. My basement walls are poured concrete, all waterproofed on the outside, and then covered in rigid foam panels with an R-10 foam surrounding entire structure, and then another  R-5 foam on the 2 side walls that are partially above grade.

The wall for the bathroom is the completely below-grade wall (attached garage abuts the top of the wall), so it has R-10 insulation with exposed concrete on the inside. I have metal studs 1/2 inch away from the concrete wall. I want to run my pex lines through the pre-drilled metal stud holes.

The internet is telling me that i need to run my pex lines on the "warm" side of the vapor barrier that i will need to install on the inside of the metal studs so that my pex lines don't freeze. Is this necessary?? Will a vapor barrier really allow the wall to get below freezing? I think it will be dubious that any of the room will be below 32 degrees given that it is R10 insulation and completely below grade. Because the garage is above the outside of this wall, i'm not even convinced that it will ever freeze on the outside of this wall anyway.

How would i even run the pex on the inside of the vapor barrier? Wouldn't my drywall be in the way?

Any help here would be appreciated. Thank you!

[bacchi]

If your rigid foam is foil-faced and taped, it's already a vapor barrier.

[nereo]

There’s a difference between a vapor barrier and a vapor retarder (i.e. Perm between 0.1 and 1).  Depending on what type of rigid foam you have, whether it’s foil faced and/or properly taped you might have a vapor barrier or a vapor retarder.

Also, while you mentioned your PEX is all below grade you didn’t state what the frost line is in your area, and how far below grade your lines are.  6” below grade in climate zone 7 is way different from 2’ below grade in zone 4.

ALso, upon re-reading your post I am unclear whether the rigid foam is on the interior or exterior of your foundation walls (or both, as with ICF construction...).

[Mgmny]

If your rigid foam is foil-faced and taped, it's already a vapor barrier.

I don't think it is foil-faced. It is blue, so that to me says no.

[Mgmny]

There’s a difference between a vapor barrier and a vapor retarder (i.e. Perm between 0.1 and 1).  Depending on what type of rigid foam you have, whether it’s foil faced and/or properly taped you might have a vapor barrier or a vapor retarder.

Also, while you mentioned your PEX is all below grade you didn’t state what the frost line is in your area, and how far below grade your lines are.  6” below grade in climate zone 7 is way different from 2’ below grade in zone 4.

ALso, upon re-reading your post I am unclear whether the rigid foam is on the interior or exterior of your foundation walls (or both, as with ICF construction...).

It is definitely taped, and all the screw holes are taped over as well. It is blue. I will go look and check on the brand.

The frost depth for my area is reported as 42". The ceilings are 9 feet, so I would guess that i might hit this threshold in the shower head where it would be at 7 feet or whatever.

The foam is on both sides of my foundation along 2 walls. 1 wall is stick framed with insulation, and the wall that the pex is run on only has 2 inches of rigid foam on the outside of the wall. I questioned the builder about this last year, and he said that it wasn't necessary to put foam on the inside because the wall is completely below grade.

[Mgmny]

[Endo1030]

If you're conditioning that space there's no way the pex lines will freeze.  Maybe what you read has something to do with condensation forming on the cold water pex lines?  I've never built with steel framing, so not sure of the details.  The best thing you can do is find a detail for basement walls that is specific to your climate and the materials you already have in place. 

I question if you really need a vapor barrier on the interior face at all.  With exterior insulation all of your drying potential may be restricted to the inside. 

How new is the construction?  the walls themselves may still be releasing a lot of moisture

[Mgmny]

If you're conditioning that space there's no way the pex lines will freeze.  Maybe what you read has something to do with condensation forming on the cold water pex lines?  I've never built with steel framing, so not sure of the details.  The best thing you can do is find a detail for basement walls that is specific to your climate and the materials you already have in place. 

I question if you really need a vapor barrier on the interior face at all.  With exterior insulation all of your drying potential may be restricted to the inside. 

How new is the construction?  the walls themselves may still be releasing a lot of moisture

We moved in August 2019. The walls were poured May 2019. The internet says they still may be drying for another year or so... This sorta makes me think adding a vapor barrior to the inside of my steel framing may be more problematic.

That said, they were happy to put the rigid foam on both sides of the concrete along with spray foam sill plate along the top, so if there is significant moisture being released, i'm not sure how much i would be causing problems if they are already doing a good job locking it in with 2 rigid foams and spray foam on top...

I personally would prefer not to put a vapor barrier up, i think it is overkill - especially because my foundation is waterproofed, but i also want ot follow code so i don't get into trouble later.

I find it dubious the pipes will freeze too, but the last thing i want is to not follow code and then have one of them freeze and burst after i tile a nice walk in shower... lol

[bacchi]

You could always borrow a laser hygrometer to check humidity levels.

Is there a thermal break between the walls and the metal studs where the pipes are going to run? Personally, I'd put rubber pipe insulation on the pex and not worry about it. As Endo1030, it's a conditioned space.

[Mgmny]

You could always borrow a laser hygrometer to check humidity levels.

Is there a thermal break between the walls and the metal studs where the pipes are going to run? Personally, I'd put rubber pipe insulation on the pex and not worry about it. As Endo1030, it's a conditioned space.

There is 1/2" between the studs and the concrete wall.

Are you saying you wouldn't worry about the pex freezing or wouldn't worry about putting up a vapor barrier?

[nereo]

You could always borrow a laser hygrometer to check humidity levels.

Is there a thermal break between the walls and the metal studs where the pipes are going to run? Personally, I'd put rubber pipe insulation on the pex and not worry about it. As Endo1030, it's a conditioned space.

There is 1/2" between the studs and the concrete wall.

Are you saying you wouldn't worry about the pex freezing or wouldn't worry about putting up a vapor barrier?

What you have is XPS rigid foam in a conditioned basement. At 2” thick and taped it qualifies a a vapor retarder with a Perm of ~0.5.  The poured walls will continue to dry out, albeit at a very low rate (and thats fine, provided they were done right in the first place). 

For comparison, 1/2” gypsum with 2 coats of latex paint has a Perm = 5, or an order of magnitude greater, so moisture that eventually migrates from your walls through the XPS will have a much easier time permeating through into your basement.  Which is what you want (your wall cavity will not become a humidity trap).

I don’t see any reason for further concern here. You’ve got a vapor retarder on the inside portion of your foundation walls, and a thermal break (gap) between the metal framing and the insulation. Just don’t go off and install another several inches of insulation on the basement side of the framing, as that could prohibit the wall’s ability to dry out and make the wall cavity colder (by blocking heat transfer from your conditions space - aka the basement - into the wall cavity)

Why did you use metal framing?  Just curious...

[Mgmny]

You could always borrow a laser hygrometer to check humidity levels.

Is there a thermal break between the walls and the metal studs where the pipes are going to run? Personally, I'd put rubber pipe insulation on the pex and not worry about it. As Endo1030, it's a conditioned space.

There is 1/2" between the studs and the concrete wall.

Are you saying you wouldn't worry about the pex freezing or wouldn't worry about putting up a vapor barrier?

What you have is XPS rigid foam in a conditioned basement. At 2” thick and taped it qualifies a a vapor retarder with a Perm of ~0.5.  The poured walls will continue to dry out, albeit at a very low rate (and thats fine, provided they were done right in the first place). 

For comparison, 1/2” gypsum with 2 coats of latex paint has a Perm = 5, or an order of magnitude greater, so moisture that eventually migrates from your walls through the XPS will have a much easier time permeating through into your basement.  Which is what you want (your wall cavity will not become a humidity trap).

I don’t see any reason for further concern here. You’ve got a vapor retarder on the inside portion of your foundation walls, and a thermal break (gap) between the metal framing and the insulation. Just don’t go off and install another several inches of insulation on the basement side of the framing, as that could prohibit the wall’s ability to dry out and make the wall cavity colder (by blocking heat transfer from your conditions space - aka the basement - into the wall cavity)

Why did you use metal framing?  Just curious...

Thank you so much for the wonderful reply. This is super helpful!

I went with metal because i read it was "easier" because everything is straight and no warping like you deal with wood. Also, a 10' metal stud in my area is ~$4.50, whereas a 10' wooden stud is $8 - so my framing material was probably about 50% of the total costif i had gone with wood. It allegedly is going to be easier for me to run the pex and electrical through as well - we will see though. I am going to need to do some extra blocking on one of the walls where i plan to hang cabinets though.

Basically, it is cheaper and lighter and cleaner to work with. Instead of using a saw for all my cuts, i just used a tin snips, made 2 cuts along the side, then bent it back and forth a few times and it snapped.

I've never framed with wood, so i can't say if it was easier or harder or what, but it definitely was cheaper than wood and i didn't have to worry about warped wood.

[nereo]

Thanks for giving your impressions re: metal framing.  I’ve never used it - I’ve only used wood studs.
For me wood is easy to use, though you do have the occasional very warped board.  All wood is crooked, some boards are just more crooked than others.  One nice thing about wood is that you can ‘pull’ it back into true with some fasteners and a hammer (within reason, of course). BUt I can see how having very straight metal pieces would be nice.

How do you hang heavy items like cabinets?  Metal-screws, obviously, but is that sufficient on its own?

[Mgmny]

Thanks for giving your impressions re: metal framing.  I’ve never used it - I’ve only used wood studs.
For me wood is easy to use, though you do have the occasional very warped board.  All wood is crooked, some boards are just more crooked than others.  One nice thing about wood is that you can ‘pull’ it back into true with some fasteners and a hammer (within reason, of course). BUt I can see how having very straight metal pieces would be nice.

How do you hang heavy items like cabinets?  Metal-screws, obviously, but is that sufficient on its own?

So, for hanging things like cabinets, which i intend to do, I guess it's largely just using toggle bolts or using wood blocking where the cabinets are and just drilling into them and that's supposed to be good enough.

[bacchi]

Don't forget insulators.

https://www.sharkbite.com/products/thru-stud-insulator

[Fishindude]

I built tons of commercial and industrial buildings and metals studs was about all we ever used.  They are a fine product if you know what you are doing.

I assume what you are wanting to do is run some plumbing lines in the outside stud walls alongside the foundation?   The Pex pipes go inside the insulation and you simply drill or punch holes thru the metal studs (if there aren't pre-existing holes) then run the PEX through the holes much like you would in a wood framed walls.   The insulators suggested above are a good idea so the sharp edge of the studs don't wear a hole in the plastic Pex over time.

Regarding hanging cabinets or anything substantial on these walls, it is wise to run 2x4 or 2x6 wood blocking between the studs / behind the drywall where you need to hang things.   This would include cabinets, chair railings, door bumpers, fire extinguishers, or just about anything heavy.   Pictures and light items can be hung from the drywall using moly type fastener inserts.   If you have a whole bunch of heavy stuff you want to hang but are unsure exactly where, it's a good idea to install a layer of plywood on the entire wall behind the drywall to anchor to.

[Mgmny]

Don't forget insulators.

https://www.sharkbite.com/products/thru-stud-insulator

Yes! I have these: https://www.menards.com/main/electrical/conduit-conduit-fittings-raceways/conduit-fittings/metal-stud-bushings-25-bag/sb13-25/p-1444424266703.htm

I only really considered them for electrical though. I guess it would make sense that i would want them for pex too...

[Mgmny]

I built tons of commercial and industrial buildings and metals studs was about all we ever used.  They are a fine product if you know what you are doing.

I assume what you are wanting to do is run some plumbing lines in the outside stud walls alongside the foundation?   The Pex pipes go inside the insulation and you simply drill or punch holes thru the metal studs (if there aren't pre-existing holes) then run the PEX through the holes much like you would in a wood framed walls.   The insulators suggested above are a good idea so the sharp edge of the studs don't wear a hole in the plastic Pex over time.

Regarding hanging cabinets or anything substantial on these walls, it is wise to run 2x4 or 2x6 wood blocking between the studs / behind the drywall where you need to hang things.   This would include cabinets, chair railings, door bumpers, fire extinguishers, or just about anything heavy.   Pictures and light items can be hung from the drywall using moly type fastener inserts.   If you have a whole bunch of heavy stuff you want to hang but are unsure exactly where, it's a good idea to install a layer of plywood on the entire wall behind the drywall to anchor to.

"The Pex pipes go inside the insulation." I guess i wasn't planning on running insulation between the studs - people above even told me not to... Do you think it's necessary?

The plywood seems like a good idea, though it could get expensive. I think i just need to be smart about where i'm putting it. Along the wall i'm going to run cabinets and along the wall i plan to put a tv.

[Bradfurd]

I just finished my basement with metal studs and XPS on the walls as well. It went smoothly. Doing all of the framing at night without power tools (only snips and a utility knife as mentioned by OP) was priceless while my two little ones slept upstairs. I can carry a bundle of studs on each shoulder without issue and every one was perfect. Glad to see someone else doing it too!

[Mgmny]

I just finished my basement with metal studs and XPS on the walls as well. It went smoothly. Doing all of the framing at night without power tools (only snips and a utility knife as mentioned by OP) was priceless while my two little ones slept upstairs. I can carry a bundle of studs on each shoulder without issue and every one was perfect. Glad to see someone else doing it too!

Yeah i have two as well (2.5 and 0.5), and a saw would not be ideal...

 

[Fishindude]

"The Pex pipes go inside the insulation." I guess i wasn't planning on running insulation between the studs - people above even told me not to... Do you think it's necessary?

I'm really having a hard time understanding the original question.  I see insulation (blue board) on those outside walls.  My only point is that you want the plumbing on the heated side of that insulation.   There is no need to insulate any of the other wall stud cavities.

The plywood seems like a good idea, though it could get expensive. I think i just need to be smart about where i'm putting it. Along the wall i'm going to run cabinets and along the wall i plan to put a tv.

Metal studs and / or drywall will not support the weight of cabinets a TV, or anything significant.   You have to install full wood blocking between the studs, or plywood as suggested.   If not, your cabinets are likely to fall off the wall.

[Mgmny]

"The Pex pipes go inside the insulation." I guess i wasn't planning on running insulation between the studs - people above even told me not to... Do you think it's necessary?

I'm really having a hard time understanding the original question.  I see insulation (blue board) on those outside walls.  My only point is that you want the plumbing on the heated side of that insulation.   There is no need to insulate any of the other wall stud cavities.

The plywood seems like a good idea, though it could get expensive. I think i just need to be smart about where i'm putting it. Along the wall i'm going to run cabinets and along the wall i plan to put a tv.

Metal studs and / or drywall will not support the weight of cabinets a TV, or anything significant.   You have to install full wood blocking between the studs, or plywood as suggested.   If not, your cabinets are likely to fall off the wall.

I'm trying to understand if I run my pex through my metal studs:
A) is it an issue if i install a vapor barrier between the stud and the room as recommended by building resources (i.e. will my pex freeze? I've read pex needs to be on the inside of the vapor barrier, but this would make installation technically challenging/impossible)

B) do I even need a vapor barrier?

[Fishindude]

A vapor barrier is just a film of plastic with little insulation value so it won't stop much heat transfer.  Inside a basement like that, pipes are very unlikely freeze regardless.
I really don't see much need for the vapor barrier.
 

[Mgmny]

A vapor barrier is just a film of plastic with little insulation value so it won't stop much heat transfer.  Inside a basement like that, pipes are very unlikely freeze regardless.
I really don't see much need for the vapor barrier.

Thank you!