# Condensation behind Insulation



## gpas233 (Feb 15, 2021)

I've been installing some Rockwool (R14) insulation in front of the rigid I installed before framing but came across something that does not look good for closing this in. It's been generally about -10 to -20 C in Edmonton the last couple weeks, and I noticed this starting to happen. Attached a couple photos showing the beads of water coming down after I pulled back some of the Rockwool after 4-5 days.

This seems to be in the same areas I've had beads of condensation running down the concrete when it's winter, but now I'm a bit hesitant to close this in. My hope was that the rigid foam would stop this from happening, but now not sure exactly what I should do. I did pick up a Smart Barrier to hopefully allow the walls to breathe somewhat if moisture ever accumulates, but this seems to be more that what that would be able to handle. Any thoughts advice on how to proceed would be appreciated.


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## Nealtw (Jun 22, 2017)

Did you have a gap between the foam board and the insulation? 
Did you fire stop the top of the wall. 
Your problem is the wall is breathing too much.


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## gpas233 (Feb 15, 2021)

The foam board is completely sealed at the top & bottom/sides with beads of canned sprayfoam. The top of the wall and rim joists were also recently completely sprayfoamed after framing - attached another photo of this.


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## stick\shift (Mar 23, 2015)

My guess is the foam is not thick enough.


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## Nealtw (Jun 22, 2017)

gpas233 said:


> The foam board is completely sealed at the top & bottom/sides with beads of canned sprayfoam. The top of the wall and rim joists were also recently completely sprayfoamed after framing - attached another photo of this.


When you have 2 insulations, what is the temp between them.
Condensation happens when warm moist air contacts a cold surface.
Warm moist air from the house got behind the first insulation where it came in contact with the cold foam board.

The test would be to insulate and completely seal so no air could get in and after some time check and see if you have condensation.


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## jim_bee (Feb 23, 2021)

If the surface of the foam is cold enough for condensation to form, it isn't thick enough. I see one layer of R-5 insulation, which works here in Virginia, in climate zone 4. In climate zones 5 & 6, the foam should be at least R-7.5 and in climate zone 8 at least R-10. If you can pull the framed wall out enough, you may be able to temporarily remove a couple of studs and slide in another layer of R-5.


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## Nealtw (Jun 22, 2017)

jim_bee said:


> If the surface of the foam is cold enough for condensation to form, it isn't thick enough. I see one layer of R-5 insulation, which works here in Virginia, in climate zone 4. In climate zones 5 & 6, the foam should be at least R-7.5 and in climate zone 8 at least R-10. If you can pull the framed wall out enough, you may be able to temporarily remove a couple of studs and slide in another layer of R-5.


He had insulation in front of the foam so there is no heat to keep the inside of the foam warm. 
Insulation in the wall in front of the insulation is fine but the water is coming from air, he has to stop the air.


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## jim_bee (Feb 23, 2021)

If you have enough foam to keep reduce the heat loss from the basement to the outside wall, the interior side of the foam will not be cold enough to condense vapor. My experience and everything I've read for several years, says to not put a vapor barrier over the framing when using foam insulation over the basement wall followed by framing and fiberglass or rock wool insulation. That creates a double vapor barrier with the potential to trap moisture between the polyethylene and the foam insulation. There is still vapor drive from the soil toward the heated basement air and at some point in the wall, the temperature differential can create condensation. 

*Keeping The Heat In - Section 6: Basement insulation: floors, walls and crawl spaces*


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## gpas233 (Feb 15, 2021)

Thanks for the replies, Jim - to address that last post I chose the Smart Barrier for that reason to address this as it's a requirement for us to have a vapor barrier outside the insulated wall, just under drywall. I also don't think the 1 inch thickness of GPS insulation I used technically qualifies as a V.B. In hindsight, I should have gone maybe a bit thicker with it. I was thinking it should be enough to provide some continuous insulation with the Roxul providing the rest, but wasn't really thinking this condensation could form again (assuming my R14 batt insulation would keep it cold enough to prevent the condensation). There is room in some areas for additional foam but not others (the concrete walls weren't completely even to begin with) where it's tighter to the framing.

I think for now I will take Neal's advice and seal off a section with full insulation and Vapor Barrier (Membrain Smart Barrier) and see how it performs over a good extreme cold and warming cycle. In the area I will also seal the studs in the 'test area' with canned foam to ensure that no warm/moist air gets behind the Roxul batts.

I think one of the issues is our humidity in the house is about 55-60% most of the time (main floor), but basement could be a bit lower than that.


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## Nealtw (Jun 22, 2017)

jim_bee said:


> If you have enough foam to keep reduce the heat loss from the basement to the outside wall, the interior side of the foam will not be cold enough to condense vapor. My experience and everything I've read for several years, says to not put a vapor barrier over the framing when using foam insulation over the basement wall followed by framing and fiberglass or rock wool insulation. That creates a double vapor barrier with the potential to trap moisture between the polyethylene and the foam insulation. There is still vapor drive from the soil toward the heated basement air and at some point in the wall, the temperature differential can create condensation.
> 
> *Keeping The Heat In - Section 6: Basement insulation: floors, walls and crawl spaces*


If you do not let moisture in, what moisture are you trapping? 
Double sealed windows do not let air in and when you lose the seal and moisture does get in, it never breaths out.


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## Nealtw (Jun 22, 2017)

gpas233 said:


> Thanks for the replies, Jim - to address that last post I chose the Smart Barrier for that reason to address this as it's a requirement for us to have a vapor barrier outside the insulated wall, just under drywall. I also don't think the 1 inch thickness of GPS insulation I used technically qualifies as a V.B. In hindsight, I should have gone maybe a bit thicker with it. I was thinking it should be enough to provide some continuous insulation with the Roxul providing the rest, but wasn't really thinking this condensation could form again (assuming my R14 batt insulation would keep it cold enough to prevent the condensation). There is room in some areas for additional foam but not others (the concrete walls weren't completely even to begin with) where it's tighter to the framing.
> 
> I think for now I will take Neal's advice and seal off a section with full insulation and Vapor Barrier (Membrain Smart Barrier) and see how it performs over a good extreme cold and warming cycle. In the area I will also seal the studs in the 'test area' with canned foam to ensure that no warm/moist air gets behind the Roxul batts.
> 
> I think one of the issues is our humidity in the house is about 55-60% most of the time (main floor), but basement could be a bit lower than that.


Your floor will always be in the mid 60* F so that cools the house air in the basement and that drives the humidity up.
I am thrilled that you will be doing the test. Do two, do one the same as what you had this time, so you will have apples to compare to apples.


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## gpas233 (Feb 15, 2021)

This may not be the most informed question, but when all is said and done - would you expect some condensation to be on the drywall? Or should the insulation (total R19 according to the ratings) be enough between the cold concrete & exterior to the warm side, to prevent this from happening on the wall face or within the wall assembly.


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## Nealtw (Jun 22, 2017)

gpas233 said:


> This may not be the most informed question, but when all is said and done - would you expect some condensation to be on the drywall? Or should the insulation (total R19 according to the ratings) be enough between the cold concrete & exterior to the warm side, to prevent this from happening on the wall face or within the wall assembly.


If you seal the wall, the only moisture in the wall will be what you leave in the wall. 
If you have holes so air can get in and all the way to the cold side of the insulation you will have condensation. 
1.Sometimes you will find moisture and mold on the painted side of the drywall. That can be caused by 2 things. 
Inside a closet or behind furniture where warm air is not circulating to combat the cold and over time no amount of insulation would help. 
2.Holes in the insulation in the wall so cold can get to the back side of the drywall.


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## jim_bee (Feb 23, 2021)

Nealtw said:


> If you do not let moisture in, what moisture are you trapping?


That is true, but if you have any air movement into the wall, you have moisture. Theoretically, if you could create a vacuum in the wall between two vapor barriers, like a thermos, you wouldn't have to worry about it. But, the foam insulation is a vapor retarder and not totally impermeable to vapor movement. Concrete is not vapor impermeable and vapor will carry moisture that will condense on a cold surface if it is trapped in the wall.


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## Bud9051 (Nov 11, 2015)

@jim_bee great link, but it will take me time to read it in detail. Even the experts change their minds. In just my quick skim through some of it I see some details that need discussion, such as earth being a poor insulator. What earth lacks for r-value per inch (standard measure for insulation) it makes up for by having many feet of soil between the heat and the cold air. More later.

Bud


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## Nealtw (Jun 22, 2017)

jim_bee said:


> That is true, but if you have any air movement into the wall, you have moisture. Theoretically, if you could create a vacuum in the wall between two vapor barriers, like a thermos, you wouldn't have to worry about it. But, the foam insulation is a vapor retarder and not totally impermeable to vapor movement. Concrete is not vapor impermeable and vapor will carry moisture that will condense on a cold surface if it is trapped in the wall.


Air movement in the wall can not make water, what water are you talking about? 
Warm air evaporates water so it can condense. You have to have a source of water for that to happen. 
Wall that breath also suck air, in cold weather any cold air in the wall will contract and suck in moist air from the house. 
As we know moisture that gets in the wall like that stays there. Stop the air, problem solved.


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## SPS-1 (Oct 21, 2008)

stick\shift said:


> My guess is the foam is not thick enough.





jim_bee said:


> If the surface of the foam is cold enough for condensation to form, it isn't thick enough.


What they said.

R5 in Edmonton is nothing.
Putting Rockwool on the interior side of the foamboard does not accomplish anything if there is no vapor barrier on the "warm in winter" side.
So what is happening here is the inside face of the foamboard gets very cold (because R5 is nothing) and warm moist air goes right through the rockwool and condenses on the foamboard.
I'm not sure if that foamboard is or is not a vapor barrier, but you are best with one vapor barrier, not two.
You need to do more research on how to insulate a basement in Edmonton. How we do things here in the sunny south may not translate very well to Edmonton.


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## gpas233 (Feb 15, 2021)

Thanks for the replies. It's a more expensive option at this point, but I'm wondering if the best bet is just adding a couple inches of sprayfoam to cover everything.

I could still return 9 bundles of Rockwool I haven't opened yet.


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## SPS-1 (Oct 21, 2008)

Give a call to a local outfit that does sprayfoam, and ask for their recommendation. Of course their recommendation will start with sprayfoam, but you will have a better idea of what is good practise in your climate.

I have two inches of closed cell sprayfoam (about R10-12) and then R13 fiberglass over that. But I am in Southwestern Ontario and my basement walls are not going to get anywhere near as cold as yours will.

Know anybody with a new house ? -- minimum code for new houses is one way to determine what is reasonable in your area. (you might even be able to find it on the internet)


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## XSleeper (Sep 23, 2007)

That is pretty normal in the winter when you don't have the drywall on yet. All your warm moist air is simply condensing and freezing on your sheathing. Once your poly vapor barrier is installed and the drywall is on it will quit doing that.


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## gpas233 (Feb 15, 2021)

That makes sense. The weird thing is that the condensation actually doesn't come back with the Rockwool pulled down and the other room that had just boardfoam had none as well. I wonder what putting the Rockwool up is doing that brings out the droplets of water - again full disclosure I'm a relative Building Science newbie


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## SLSTech (Jan 19, 2021)

Part of the issue is you have warm moist air from inside hitting the foam directly (which is a condensing surface unlike the batts) - in order for any type of batt insulation to work properly it must be fully enclosed on all 6 sides. The amount of foam you do have is not enough - you need enough to push the condensation point outside or reduce any chances to only extreme events. Based on a quick look at your temp ranges I would compare you to at least a climate zone 5 here which would mean for a minimum code compliant house you need at least an R10 but the more you have outside the better. 
Let me give you two pieces to review: Common Sense Building: How much insulation should I install? (thehtrc.com) & FAQ: Why are my windows / walls wet or have ice on them? (thehtrc.com)


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## XSleeper (Sep 23, 2007)

The rockwool is blocking the cold exterior wall from the heat source inside, so the foam is colder with the insulation than it is without. Colder surfaces will collect more frost.


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## SPS-1 (Oct 21, 2008)

gpas233 said:


> I wonder what putting the Rockwool up is doing that brings out the droplets of water


Nothing. The moist air flows right through the rockwool.


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## SPS-1 (Oct 21, 2008)

SLSTech said:


> I would compare you to at least a climate zone 5 here which would mean for a minimum code compliant house you need at least an R10 but the more you have outside the better.


THIS outfit in Edmonton pushes their 2.5" R-13 foam.

Edmonton re-defines the word cold. It's supposed to hit -27 F tonight, and winter won't officially start for over two weeks.


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## jim_bee (Feb 23, 2021)

Nealtw said:


> Air movement in the wall can not make water, what water are you talking about?


Under normal circumstances all air has moisture, we just don't see it until it condenses.


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## jim_bee (Feb 23, 2021)

Bud9051 said:


> Even the experts change their minds. In just my quick skim through some of it I see some details that need discussion,


Great. I'm always interested in learning something new. I try to keep up with the latest consensus and don't mind finding out I've missed something.

I posted that specific link because it's from Canada, same as the OP. For the technique he used, see section 6.2.4 of the document.


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## jim_bee (Feb 23, 2021)

gpas233 said:


> hanks for the replies. It's a more expensive option at this point, but I'm wondering if the best bet is just adding a couple inches of sprayfoam to cover everything.


i agree with SPS-1's advice above. That would be an option, provided that you still provide the required R value over all.


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## SPS-1 (Oct 21, 2008)

gpas233 said:


> I think one of the issues is our humidity in the house is about 55-60% most of the time (main floor), but basement could be a bit lower than that.


That's very high for winter.
More likely, the humidity is higher in the basement. Assuming the absolute humidity is consistent through the house, if the temperature is lower in the basement, the relative humidity will be higher.


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## ddsrph (Nov 23, 2013)

Would it be practical to use all foam in the wall. You can cut polyiso boards and fit tightly into stud cavities or more expensive spray foam. I did my partial underground block and brick house using recycled polyiso and have had no problems. Walls have 6 inches of foam board between block and Sheetrock with board joints overlapped and taped. With a similar attic insulation I heat and cool for about $50 per month with 1 1/2 ton heat pump. Check out my thread in showcase section under “partial earth sheltered home”


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## gpas233 (Feb 15, 2021)

I was thinking along those same lines that one option could be installing another R10, 2" of GPS foamboard (same as what I used) and sealing around the edges/behind the studs with canned foam bringing it up to R15 total. That would be for the walls susceptible to frost. Hopefully I could just leave the walls where they are and build it into the stud bays - the tightest studs are right up against the 1" foam. I attached a markup of the areas of the basement that I've seen some moisture buildup over the years living here.The south facing wall has never had any condensation or frost since 2014 when I bought the house, so I think I should be safe there.

I'm waiting for the insulation company who did my rim joists to let me know about the cost of spraying over the board foam and if they think it's a good idea or not. They seem pretty good to deal with and up front, so not too worried about a complete sales pitch.


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## ddsrph (Nov 23, 2013)

gpas233 said:


> I was thinking along those same lines that one option could be installing another R10, 2" of GPS foamboard (same as what I used) and sealing around the edges/behind the studs with canned foam bringing it up to R15 total. That would be for the walls susceptible to frost. Hopefully I could just leave the walls where they are and build it into the stud bays - the tightest studs are right up against the 1" foam. I attached a markup of the areas of the basement that I've seen some moisture buildup over the years living here.The south facing wall has never had any condensation or frost since 2014 when I bought the house, so I think I should be safe there.
> 
> I'm waiting for the insulation company who did my rim joists to let me know about the cost of spraying over the board foam and if they think it's a good idea or not. They seem pretty good to deal with and up front, so not too worried about a complete sales pitch.


I bought a huge quantity of 2 1/2 inch poly iso from a commercial roof contractor for $4 a 4 by 8 sheet. On my block wall partial underground house I put 1/2 XPS blue board against the block then the rest overlapped joints of the polyiso. I also bought some reclaimed 1 1/2 inch poly iso. Before any framing I placed the 1/2 inch XPS then sheets of 1 1/2 poly iso for a continuous 2 inches total. Then framed walls against the 2 inches and carefully cut polyiso to fill all cavities. My utility bill for heat pump is estimated to be about $50 per month. Have had zero moisture problems. I live in southern TN which has very variable weather. Been near 70 for highs past three days but could just as easily be highs in 30’s.


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## gpas233 (Feb 15, 2021)

It seems I can install the lower batts without condensation (soil against those walls), condensation only occurs higher up on the exposed walls which are the coldest. I've isolated a section with canned foam behind the studs and will see how it performs before drywalling sometime in the new year. As long as I don't feel any major condensation after a stretch of -20 C or so (very common here, although it's a balmy -8 C right now), I think I should be fine. I pretty much know which walls stay the coldest from the previous winters (same areas appear to sweat each year), so those will be the spots I check.

If I ever break the vapour barrier seal with nail holes or anything in the future would that be anything to worry about - or am I overthinking it a bit?

I also haven't used the MemBrain smart barrier I bought before, but I'm assuming it doesn't let any vapour in - just allows some out.


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## Nealtw (Jun 22, 2017)

gpas233 said:


> It seems I can install the lower batts without condensation (soil against those walls), condensation only occurs higher up on the exposed walls which are the coldest. I've isolated a section with canned foam behind the studs and will see how it performs before drywalling sometime in the new year. As long as I don't feel any major condensation after a stretch of -20 C or so (very common here, although it's a balmy -8 C right now), I think I should be fine. I pretty much know which walls stay the coldest from the previous winters (same areas appear to sweat each year), so those will be the spots I check.
> 
> If I ever break the vapour barrier seal with nail holes or anything in the future would that be anything to worry about - or am I overthinking it a bit?
> 
> I also haven't used the MemBrain smart barrier I bought before, but I'm assuming it doesn't let any vapour in - just allows some out.


Below frost depth the wall is warmer. Do that test we talked about.


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## gpas233 (Feb 15, 2021)

Nealtw said:


> Below frost depth the wall is warmer. Do that test we talked about.


I'll be sealing up a section (same location I experienced the condensation) about 11 foot long this Saturday and checking it as it gets colder again.

Just have to get the wife calmed down that I'm not drywalling yet... lol


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## Nealtw (Jun 22, 2017)

gpas233 said:


> I'll be sealing up a section (same location I experienced the condensation) about 11 foot long this Saturday and checking it as it gets colder again.
> 
> Just have to get the wife calmed down that I'm not drywalling yet... lol


I would take a piece of insulation and cover it with sheet poly all taped and seal to the foam and surround with insulation that is not sealed. 
There are some here that would like to see me proved wrong. No air in, no condensation. Anyone else offering any proof of anything.


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## Akcabin (5 mo ago)

I believe that the r5 continues insulation is a good thermal barrier. The rockwool between the studs is good. 
A visqueen vapor barrier with seams taped. Drywall seams and nail holes done up. Pool table might be nice. 
The ridgid foam is not a vapor barrier but considered a retarder. As it can stop a lot but not everything. So installing visqueen over it all will be a barrier. Use only enough staples to hold it in place. 
Hey good luck if you haven't completed it. And this is only my thoughts. I happened to be researching ridgid insulation also


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## ddsrph (Nov 23, 2013)

gpas233 said:


> It seems I can install the lower batts without condensation (soil against those walls), condensation only occurs higher up on the exposed walls which are the coldest. I've isolated a section with canned foam behind the studs and will see how it performs before drywalling sometime in the new year. As long as I don't feel any major condensation after a stretch of -20 C or so (very common here, although it's a balmy -8 C right now), I think I should be fine. I pretty much know which walls stay the coldest from the previous winters (same areas appear to sweat each year), so those will be the spots I check.
> 
> If I ever break the vapour barrier seal with nail holes or anything in the future would that be anything to worry about - or am I overthinking it a bit?
> 
> I also haven't used the MemBrain smart barrier I bought before, but I'm assuming it doesn't let any vapour in - just allows some out.


That’s why absolute vapor barriers are not recommended by many experts. They always leak to some extent and trap moisture. Try to find articles by “Building Science” they have a good discussion using 5 different examples of insulation techniques specifically addressing basement insulation. I used that info when I was building my partial earth sheltered 1200 sq foot house.


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## gpas233 (Feb 15, 2021)

Nealtw said:


> I would take a piece of insulation and cover it with sheet poly all taped and seal to the foam and surround with insulation that is not sealed.
> There are some here that would like to see me proved wrong. No air in, no condensation. Anyone else offering any proof of anything.


I plan to do the full wall to see how the assembly works for the coldest weather we get, but may also do this second test. I'll try Rockwool in the same area of the next bedroom where the condensation has also been noticable in the past, with out vapour barrier. Even putting up one batt in a stud bay last night leads to condensation behind it.


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## XSleeper (Sep 23, 2007)

gpas233 said:


> I'll try Rockwool in the same area of the next bedroom where the condensation has also been noticable in the past


What is that saying about doing something twice and expecting a different result? What's baffling is why you think this is so complicated. If you put up insulation, you need to cover it with a vapor barrier (and drywall) as soon as possible, because its going to get frost on the cold exterior sheathing if you wait any prolonged period of time... like even overnight. I fail to see why you need to "test" this, it's building science. Unless you just need to prove that what we are telling you is true. More foam thickness on the exterior sheathing would be a good thing. You don't want the dewpoint ever being crossed within your wall cavity.


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## carpdad (Oct 11, 2010)

Once you drywall the problem will go away. Even better will be caulk the stud edges, top and bottom plates when drywalling. Caulk/foam around electrical boxes. Use oil base primer and 2 coats of good acrylic paint. Paint also gives some vapor retarder factors. Make sure gaps between foam board and stud wall is sealed with spray foam. Basically, seal any gap, even if just a crack or looks like a tight joint, between foam board and rockwool. I sealed all sides of the foam board against the foundation too. Fire blocking later.
BTW, insulation does NOT stop heat/cold transfer. It just slows it down. If your outside is cold enough, it WILL overcome the heating inside. If very cold, you just have to heat more inside. 
Though effectiveness of plastic vapor barrier is mentioned in above post, I would use it and do a very good job. But keep in mind that you have 2 layers of insulation and both must be air sealed very well to avoid air movement and accompanying moisture.
Electrical boxes, maybe using plastic boxes since they have less holes. Caulk/foam around the cable clamps.
What I said about problem going away is on faith. You can do the best you can and hope for best.


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## gpas233 (Feb 15, 2021)

Nealtw said:


> I would take a piece of insulation and cover it with sheet poly all taped and seal to the foam and surround with insulation that is not sealed.
> There are some here that would like to see me proved wrong. No air in, no condensation. Anyone else offering any proof of anything.


Here are a few photos of different tests this week. The full wall test was still condensing on the foam after the first day, but I've left it alone now for a few days. I did my best to tape all the edges, but didn't want to mess around with acoustical sealant if I end up pulling it off later.


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## Nealtw (Jun 22, 2017)

So have you removed this and found condensation behind the insulation?


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## gpas233 (Feb 15, 2021)

I opened a slit in the vapor barrier and reached behind the full wall I did after day1 and still felt condensation on the foam board. I was thinking it could be some remaining humidity in the wall, so might be best to check after a few days. I haven't checked the 2 batts I put up with poly wrap yet. 

I did check with a local insulation contractor (same guy who did my rim joists) and he said they sometimes spray foam these problem areas above grade, then batt and poly below grade if the home owner wants to save some money.


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## Bud9051 (Nov 11, 2015)

I apologize in advance but I have avoided this thread because you are doing so many things wrong and the advice you are getting is poor. Why am I posting now? Because those pictures show you are confusing vapor barrier and air barrier. It is the air barrier you need and plastic without a "RIGID" air barrier does not work. Feel free to ignore me as you seen set on your path.

Bud


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## Nealtw (Jun 22, 2017)

gpas233 said:


> I opened a slit in the vapor barrier and reached behind the full wall I did after day1 and still felt condensation on the foam board. I was thinking it could be some remaining humidity in the wall, so might be best to check after a few days. I haven't checked the 2 batts I put up with poly wrap yet.
> 
> I did check with a local insulation contractor (same guy who did my rim joists) and he said they sometimes spray foam these problem areas above grade, then batt and poly below grade if the home owner wants to save some money.


Are you sure you felt wet, or did it just feel cold?


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## gpas233 (Feb 15, 2021)

Nealtw said:


> Are you sure you felt wet, or did it just feel cold?


It felt wet for sure.


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## Nealtw (Jun 22, 2017)

gpas233 said:


> It felt wet for sure.


It looks like the bat was tight against the foam board. In order to have vapour condense out of the air, you need air in the cold area.


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## gpas233 (Feb 15, 2021)

Nealtw said:


> It looks like the bat was tight against the foam board. In order to have vapour condense out of the air, you need air in the cold area.


I just felt behind the full wall (top right of photo), it was still wet on the foam in the 2 spots I checked.

The other two sample areas with the batts and poly were both wet, but seemed less wet than the batt beside it with no poly. I moved the sample batts a bit more off the foam in case that was causing any problems.


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## Nealtw (Jun 22, 2017)

gpas233 said:


> I just felt behind the full wall (top right of photo), it was still wet on the foam in the 2 spots I checked.
> 
> The other two sample areas with the batts and poly were both wet, but seemed less wet than the batt beside it with no poly. I moved the sample batts a bit more off the foam in case that was causing any problems.


When we want to check concrete for leaks we seal a sheet poly to it, if we have water behind the poly we have a leak in the concrete. Are you sure the insulation is dry when you started the test?


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## jim_bee (Feb 23, 2021)

To be a bit repetitious, see this article from Journal of Light Construction: Condensation Control in Basements


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## gpas233 (Feb 15, 2021)

jim_bee said:


> To be a bit repetitious, see this article from Journal of Light Construction: Condensation Control in Basements


I have read up quite a bit on this, and did prior to installing the 1” foam. At the time I acknowledged I would have to install a vapour barrier and planned on it. That was the trade off for the extra space in small-ish basement. I guess I didn’t plan on a scenario where I would have continual condensation with a Vapor barrier up.

Besides being labor-intensive, does anyone see a downside in ‘cut and cobble’ additional R10 GPS insulation into the stud bays where I’ve had condensation (about half the basement)? I was thinking I could test a corner and cover with drywall for a couple weeks and see how it performs with no Vapor barrier. I would leave the walls where they are, but use canned foam behind the studs to fill in the gaps. It would be R15 between the studs with the R5 + R10 foam I would be adding.


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## XSleeper (Sep 23, 2007)

You can't go wrong with more rigid foam. The idea being that the more rigid foam you have, the warmer the interior surface of the foam is, the less likely it will be to condense vapor inside the wall on that cold(er) surface.


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## jim_bee (Feb 23, 2021)

Keeping the interior surface above the dewpoint will prevent condensation. A previous post noted that R10 is recommended for your climate zone, so R15 should be sufficient.


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## gpas233 (Feb 15, 2021)

jim_bee said:


> Keeping the interior surface above the dewpoint will prevent condensation. A previous post noted that R10 is recommended for your climate zone, so R15 should be sufficient.


The downside is I won’t have enough room for the Roxul, unless I furr out the studs. I kind of like the idea of leaving it open to dry if ever needed, so leaning towards leaving it at the R15 foam and calling it a day for those walls.

Any concerns about leaving the walls where they are? (Lots of work to move them now, based on how it’s framed). Tightest spots are just over 1” from the concrete. That’s what the spray foam guys here space the walls off concrete so I feel it should be okay, I was just thinking of the possibility of moisture on the studs due to only having the R5 behind them.


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## Jeffdmc1 (Dec 5, 2020)

XSleeper said:


> What is that saying about doing something twice and expecting a different result? What's baffling is why you think this is so complicated. If you put up insulation, you need to cover it with a vapor barrier (and drywall) as soon as possible, because its going to get frost on the cold exterior sheathing if you wait any prolonged period of time... like even overnight. I fail to see why you need to "test" this, it's building science. Unless you just need to prove that what we are telling you is true. More foam thickness on the exterior sheathing would be a good thing. You don't want the dewpoint ever being crossed within your wall cavity.


Hi Gpas.
I've been listening in because I have my own flying circus going on in the Chicago area.
I'd like to get your thoughts on insulating an unfinished basement.
Presently, the concrete foundation walls are framed out with 2x4's with a 1",or so, gap between the studs and concrete wall. Unfaced R13 was installed in the joists space with an FSK blanket stapled with 1000's of staples. I opened it up, because there is another problem going on, and did not detect any mold, stain or smell.
I would think that the many staples, should be taped over, along with the top and bottom plate areas. Unfortunately, the ceiling is only framed with webbed joists and difficult to seal the area above the insulated wall. 
The home is 3 years old.

Also, relating to rim joist insulation, if there is 2-3" of spray foam, is a vapor or batt insulation necessary? I don't mind it being a little cooler with foam alone, as long as, no moisture is coming in.

Thank you for any comments.


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## gpas233 (Feb 15, 2021)

Jeffdmc1 said:


> Hi Gpas.
> I've been listening in because I have my own flying circus going on in the Chicago area.
> I'd like to get your thoughts on insulating an unfinished basement.
> Presently, the concrete foundation walls are framed out with 2x4's with a 1",or so, gap between the studs and concrete wall. Unfaced R13 was installed in the joists space with an FSK blanket stapled with 1000's of staples. I opened it up, because there is another problem going on, and did not detect any mold, stain or smell.
> ...


Hi Jeff, there are others on here that may be able to help you better than I can. I would say best bet is to start a new post into the forum if you haven’t already.

I beleive that should be plenty thick for the spray foam not to need a separate barrier.

I would say post some photos of the insulation blanket. I don’t have much experience with those, just what I’ve seen in some videos.

Cheers,
Greg.


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## Jeffdmc1 (Dec 5, 2020)

gpas233 said:


> Hi Jeff, there are others on here that may be able to help you better than I can. I would say best bet is to start a new post into the forum if you haven’t already.
> 
> I beleive that should be plenty thick for the spray foam not to need a separate barrier.
> 
> ...


Thank you and I'll do that.
Happy New Year!!


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## gpas233 (Feb 15, 2021)

For the walls with condensation I've completed a section of how I intend to complete them. Any visible problems with the approach I'm taking here? Aside from taking more time, I believe it should perform comparably to spray foam. I'm at R20 (5+10+5 above grade, where the condensation was happening) and R15 below grade for the bottom 3 feet - left it that way due to the wiring.


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## Bud9051 (Nov 11, 2015)

From what I can see you are going to be warm and toasty.
I usually recommend most insulation (when codes will allow it) above grade down to one or two feet below grade. Below that the earth provides a huge amount of insulation value.
Good Job
Bud


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## jim_bee (Feb 23, 2021)

Looks good. Nice, neat installation.


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## gpas233 (Feb 15, 2021)

Bud9051 said:


> From what I can see you are going to be warm and toasty.
> I usually recommend most insulation (when codes will allow it) above grade down to one or two feet below grade. Below that the earth provides a huge amount of insulation value.
> Good Job
> Bud


Thanks for the feedback Bud. I think im about 2 feet below grade just looking out the closest window, but will keep that in mind.


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