[Leo55]

Hey guys, I'm in the middle of a big remodel, and am working with existing 2x4 exterior walls. I live in climate zone 5, in central Ohio, where we get a lot of precipitation. It gets both pretty hot and pretty cold.

The house exterior is vinyl siding, with house wrap, and OSB. On the interior, everything is stripped to the studs. The old drywall had a plastic sheet under it, and lots of the old insulation was moldy. The old insulation was fiberglass batts.

Does anyone have any suggestions for how best to insulate these walls? Spray foam could be an option, although I am concerned about condensation forming in the wall.

I could fur the wall out to make it a 2x6 wall, and insulate that. The house is very small. VERY small. Just about 800 sq ft. I really don't want to make the rooms any smaller than they already are if it wouldn't make a big difference.

Any thoughts would be much appreciated.

 

[Nealtw]

Hey guys, I'm in the middle of a big remodel, and am working with existing 2x4 exterior walls. I live in climate zone 5, in central Ohio, where we get a lot of precipitation. It gets both pretty hot and pretty cold.

The house exterior is vinyl siding, with house wrap, and OSB. On the interior, everything is stripped to the studs. The old drywall had a plastic sheet under it, and lots of the old insulation was moldy. The old insulation was fiberglass batts.

Does anyone have any suggestions for how best to insulate these walls? Spray foam could be an option, although I am concerned about condensation forming in the wall.

I could fur the wall out to make it a 2x6 wall, and insulate that. The house is very small. VERY small. Just about 800 sq ft. I really don't want to make the rooms any smaller than they already are if it wouldn't make a big difference.

Any thoughts would be much appreciated.

You need 2 things to get condensation in the wall. Warm moist air and a cold surface. Wet dirty or moldy insulation would point out air leaks

If you just replace the fiberglass thickness with glass or rock wool you could add 1" foam board properly sealed would be the air barrier and add 5R and a thermal break on the studs.

 

[Colbyt]

I'll hazard a guess that is electric BB heat or some form of no forced air.


I think I read builders made a mistake in the 70's and early 80's using plastic as a vapor barrier.


Personally, I would make really sure it is dry and that any mold on the studs is killed and then go back with plain old kraft faced insulation.

 

[Leo55]

Yes, the old insulation was dirty in places, so there was air infiltration.

And yes, the old place had baseboard heating. Out of curiosity, what made you guess that?

A ductless mini-split is what I'm thinking to go to. The house sits on a slab, and there is no ductwork. It's so small, I think a mini-split might be a good solution.

Regarding the walls, do you think 1" of rigid foam on the interior would be in danger of creating a plane for condensation inside the wall? I plan to air seal the daylights out of the wall both to the exterior and interior, to eliminate as best I can gross air infiltration. But the ambient air here in the summer will still be very humid, and the inside of the place will be air conditioned. I don't know if 1" is thick enough to create enough of a thermal break so that condensation would not be a risk.

Thanks again for the thoughts. I appreciate it.

 

[Porsche986S]

Here is what I would do but I'm no expert :biggrin2: Let's say your studs are spaced at 16 " on center . Get some 3/4 " or 1 " thick rigid foam insulation and cut the foam so there is aprox. a 1/4 " gap all the way around in the stud cavity . Use a few nails/screws to hold the foam in place . Do this for all stud cavities . After all the foam board is in place take cans of spray foam like Great Stuff or whatever brand is available in your area and fill that 1/4 " gap all the way around . This will eliminate air infiltration . You may have to get a little creative around switch and outlet boxes .

I would then attach 1x furring strips to the face of the studs and then install kraft faced fiberglass insulation . Then finish with the wall product of choice . Use this same air sealing methodology for anything that goes from inside to outside like ceiling can lights as an example . The more drafts you can eliminate the better your home will feel regardless of heating or cooling .

 

[SPS-1]

We should really be more specific here. The term "foam", has been used maybe half a dozen times so far in this thread. Maybe somebody can educate me on the proper wording, but the term "foam" means nothing to me.

There is EPS, XPS, Polyiso, and polyurethane that can be purchased as board. Some of these are similar, some are very different. XPS is a good vapor barrier, EPS - not so much.

 

[Bud9051]

The readily available charts to provide some guidance for how much rigid (?) is needed have moved behind membership requirements.
https://www.greenbuildingadvisor.com/article/combining-exterior-rigid-foam-with-fluffy-insulation

My free time has expired but you can take a look.

The down side is these charts are dealing with exterior rigid and i'm not sure how easily we can apply them to an inside application, but it is a start.

Air sealing is a key to any assembly then thermal bridging. But without a continuous layer of rigid there are still major gains to be made with better insulation (like mineral wool), and a neat installation. If new siding and or new windows are somewhere in the future than exterior rigid could be considered.

Bud

 

[Leo55]

Yes, please feel free to be more specific about the rigid foam. I am not knowledgeable enough yet to be able to be more specific myself. I have not gotten that far yet. I've been mulling over the more general idea of whether or not it is advisable in my climate to have 1" of rigid foam on the interior of a 2x4 wall. I'm not sure if the wall is too thin for that, and you might get condensation between the rigid foam and the insulation.

I'm pretty sure in my area you don't need to have a vapor barrier anymore, but instead a vapor retarder, which I think can be just painted drywall.

Also, I've seen it suggested in my area that if you replace your siding, they encourage you to add 1" rigid foam with an r value of 5 to the exterior beneath the new siding.

My plan is to attend very carefully to air sealing. The old insulation was very dirty. I saw a chart not long ago that showed the curve created when heat flow was plotted against r value, and how most of the benefit occurs in the first part of the curve. My goal might be to get the wall to an r value of 20, if that would be possible. Here is a link to the page with that chart for anyone who wants to see it.

https://www.energyvanguard.com/blog/76941/The-Diminishing-Returns-of-Adding-More-Insulation


Thanks for the link to that Green Building Advisor article.

 

[APA]

Hey guys, I'm in the middle of a big remodel, and am working with existing 2x4 exterior walls. I live in climate zone 5, in central Ohio, where we get a lot of precipitation. It gets both pretty hot and pretty cold.

The house exterior is vinyl siding, with house wrap, and OSB. On the interior, everything is stripped to the studs. The old drywall had a plastic sheet under it, and lots of the old insulation was moldy. The old insulation was fiberglass batts.

Does anyone have any suggestions for how best to insulate these walls? Spray foam could be an option, although I am concerned about condensation forming in the wall.

I could fur the wall out to make it a 2x6 wall, and insulate that. The house is very small. VERY small. Just about 800 sq ft. I really don't want to make the rooms any smaller than they already are if it wouldn't make a big difference.

Any thoughts would be much appreciated.

Was the framing moldy or did the insulation just smell musty? I almost guarantee it was because of that plastic vapor barrier under the drywall. How old is the house. If it is old and hasn't rotted by now, it isn't. I would just get the newer 3.5-inch, r-15 kraft faced and staple it in. However, since the house is so small, look into spray foam. there will be no condensation with that stuff.

 

[APA]

I would say that 90% of houses in this area has some mustiness in the walls. It is a product of how they are constructed.

 

[SPS-1]

Was the framing moldy or did the insulation just smell musty? I almost guarantee it was because of that plastic vapor barrier under the drywall.

I don't understand the suggestion that a vapor barrier on the warm-in-winter side is a problem in a cold climate. The warm moist air is inside the house. The cold air outside contains very little moisture. If warm moist air hits a cold surface, it will condense to liquid water, so I can understand the desirability of a vapor barrier behind the drywall.

Things can be different in a warm climate, but OP indicated he is in Zone 5.

 

[Nealtw]

I don't understand the suggestion that a vapor barrier on the warm-in-winter side is a problem in a cold climate. The warm moist air is inside the house. The cold air outside contains very little moisture. If warm moist air hits a cold surface, it will condense to liquid water, so I can understand the desirability of a vapor barrier behind the drywall.

Things can be different in a warm climate, but OP indicated he is in Zone 5.

People have seen all kinds of problems with VB but they never consider that it was just not done properly. :vs_cool:

 

[Leo55]

Thank you guys for the thoughts.

To answer your questions---the house was built in 1985. It's very small---about 800 sq ft. The insulation was moldy, not really the framing. It seems to have been from condensation on the plastic vapor barrier.

I'm in zone 5----we get a lot of precipitation. In the summer it gets hot and muggy, and in the winter we have snaps down in single digits.

People used to run a window air conditioner in there in the summer. I think warm muggy air infiltrated the wall, and moisture condensed on the vapor barrier, which was touching the cool drywall.

I like the idea of adding 1" of some kind of foam to the wall, to create a thermal break and raise the wall's r value. I just want to be sure that I don't somehow create a situation for condensation to form.

 

[Nealtw]

Thank you guys for the thoughts.

To answer your questions---the house was built in 1985. It's very small---about 800 sq ft. The insulation was moldy, not really the framing. It seems to have been from condensation on the plastic vapor barrier.

I'm in zone 5----we get a lot of precipitation. In the summer it gets hot and muggy, and in the winter we have snaps down in single digits.

People used to run a window air conditioner in there in the summer. I think warm muggy air infiltrated the wall, and moisture condensed on the vapor barrier, which was touching the cool drywall.

I like the idea of adding 1" of some kind of foam to the wall, to create a thermal break and raise the wall's r value. I just want to be sure that I don't somehow create a situation for condensation to form.

If you are running the AC a lot then the worry is getting air from the outside in the summer. Gaps in the insulation are the real problem when you have mold inside the poly.

 

[APA]

People have seen all kinds of problems with VB but they never consider that it was just not done properly. :vs_cool:

Because it is so easy to do improperly.

 

[NotYerUncleBob2]

The poly vapor barrier is fine...if you're in Canada or Alaska. Not so much for most heating/cooling climates in the US.
For the best comfort your order of importance is to air seal, then insulate the attic, then insulate the walls.
If you're looking to break the thermal bridge and have already gutted the interior, consider the bonfiglioli wall approach: https://www.finehomebuilding.com/2014/11/26/breaking-the-thermal-bridge

 

[Nealtw]

@APA @ NotYerUncleBob2


Mold does not grow on fiberglass or poly, it grows on dust and dirt left there by passing air. So there was an air leak one or both sides of this wall.
Are you saying with out poly, there would have been no mold?

What would you blame if there was no poly?

 

[Leo55]

From what I've read it sounds like a poly vapor barrier isn't necessary where I live.

Neal, yes, there was air leakage, probably on both sides of the wall. The mold was concentrated on the surface of the insulation touching the poly vapor barrier.

I'm not sure what it would have looked like if there had been no poly. Maybe mold on the backside of the drywall? Seems like you still might have gotten some condensation, maybe just not as much? You'd still have had the air leakage, and the contact between humid air and a cool surface----just a more porous surface, the backside of the drywall.

Air sealing is high on my priority list.

 

[Nealtw]

From what I've read it sounds like a poly vapor barrier isn't necessary where I live.

Neal, yes, there was air leakage, probably on both sides of the wall. The mold was concentrated on the surface of the insulation touching the poly vapor barrier.

I'm not sure what it would have looked like if there had been no poly. Maybe mold on the backside of the drywall? Seems like you still might have gotten some condensation, maybe just not as much? You'd still have had the air leakage, and the contact between humid air and a cool surface----just a more porous surface, the backside of the drywall.

Air sealing is high on my priority list.

Yeah, air getting in the wall from either side can deposit dirt and moisture and the mold spores are everywhere.

With 2x4 walls that don't leak and are well insulated, we still can see ghosting on the walls where the dust collects where the studs are.



Dew point is the temperature where moisture in the air will condense on a cold surface.

I would think we would like to keep that temperature about the center of the wall and then if we have that we don't want any moist dirty air there.

So keeping air out of the wall is very important.
I have tried to imagine what that dew point line might look like in a wall that is done with out air leaks and remembering that the studs have a very low R value. Ghosting on the wall is when the dew point has made it all the way to the inner surface, not enough R value or poor heat circulation behind furniture, maybe.



So I tried to figure what the dew line might look like in a wall with out air leaks and the same wall with outside light or inside switch box.
I don't think it matters how you block the air as long as you are blocking it.

So this is what I imagine and I did not try to figure what would happen with air leaks.

 

[Bud9051]

Here is an article from Building Science Corp to add to the debate. For disclosure, I haven't read all of it but it has nice pictures .
https://www.buildingscience.com/doc...ng-cold-weather-condensation-using-insulation

Bud