Condensation out side top floor storm windows/new HVAC/new Spray Foam

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pt5040

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Hi all - thank you in advance for any guidance. I'm a home owner in Chicago. I live in an old brick home that was recently renovated with all new mechanicals and spray foam insulation on the top floor and attic crawl space. We also did spray foam on the rear half of the first floor.

We replaced the original furnace radiator system with two zones of forced air. Each zone has an aprilaire humidifier. Using Hygrometer that I purchased i measure relative humidity in the house around 30-40 depending on the outside weather (0-50+). Both Zones are set to 68d and with the remote thermostats the various corners of the house measure roughly that target.

We have original wood windows on the top floor and the front half of the first floor while the rear of the home has new aluminum windows. Across all the old original windows we have storm windows.

Ever since we moved back into the house, post remodel, the exterior of the top floor storm windows are completely covered in condensation (frozen or not depending on exterior temp) when the outside temp is below roughly 40d. We never had this problem before. Additionally, we do not see this issue on any of the windows on the first floor.

Is this the result of the HVAC system, the spray foam insulation, something else? And what types of remedies can I pursue - other than the exceptionally costly replacement of all old windows. I've read that the spray foam is both a thermal and vapor barrier - is the condensation the result of the fact that these old windows are now the only exit place for heat/humidity?

Thank you for any advice and please let me know if I can supply any technical details from the system or insulation if that's helpful in your advice giving.
 

Fitter30

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Moisture laden air is leaking out of the window / frame condensing on the storm window. Here's a chart for outside temp and house setting from Aprilaire. This window film might help. Box stores carry this also.
www.amazon.com/Frost-King-V73-3H-Shrink/dp/B0000CBJN3/ref=asc_df_B0000CBJN3?mcid=a42b84179ec13cd2803ca886eb425d65&tag=hyprod-20&linkCode=df0&hvadid=693499423661&hvpos=&hvnetw=g&hvrand=14932870401359996430&hvpone=&hvptwo=&hvqmt=&hvdev=t&hvdvcmdl=&hvlocint=&hvlocphy=9023792&hvtargid=pla-400889448612&psc=1
Screenshot_20250201-132928.png
 

wwhitney

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68F air with 40% relative humidity has a dew point of 43F. So whenever that air hits a surface colder than that, you will get condensation. Presumably your storm windows are single paned, so the interior surface temperature is close to the outdoor temperature, and the wood windows are quite leaky of air.

Why didn't this happen before? Presumably you had no humidifier, and your house overall may have been leakier of air when you had no spray foam. So your indoor humidity was lower in the winter, maybe 10%-20%, and the dew point was usually above the temperature of the interior face of the storm windows.

How to avoid this problem? You either need to make the wood windows less leaky of air (retrofit air sealing or replacement), or raise the temperature of the interior face of the storm windows (edit: or give up the humidifier to lower the air's dew point). That could be done by replacing them with double paned storms, assuming such a thing exists. If the new storm windows have metal frames, those would need to be thermally broken; other wise the interior face of the metal will still be cold and you'll just be moving the condensation problem from the glass to the metal.

Cheers, Wayne
 
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pt5040

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Thank you very much wwhitney. The table from aprilaire is very useful as well...I wasn't aware of this issue. One issue I had read about online is this that mold can become a problem in the attic if either the hvac isn't "tuned" to the fact that spray foam is installed. I'm not thrilled that my storms are covered in condensation (much prefer they are clear and heat isn't escaping as you point out) but would be very concerned if mold was a threat. Do you have any thoughts on what scenarios I'd need to be worried about? That is, if the humid air is escaping from the windows and condensating because it hits the cold storms that seems very different than condensation forming on the interior of 4" of spray foam as the humid air in the attic shouldn't be meeting a cold surface. Am I thinking about this correctly? Thanks
 

pt5040

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Thank you very much Fitter30. I was not aware of this table/implications of the dew point changing the recommended RH. I'll make that adjustment.
 

pt5040

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Where is the foam in the attic?
The roof is a typical pitched roof (tudor style home). The entire top floor was down to the brick. So they sprayed the underside of the roof on the wood between the joists and then all the walls of that level. The thickness was 4" or greater. They also sprayed the rear of the home on the lower level - so on that side its contiguous foam from the roof down the walls (the remodel was the result of water damage that forced the removal of original plaster walls on that side of the home).
 

wwhitney

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So if the underside of the roof deck is sprayed, and if the attic is unventilated (as would be suggested by the attic being inside the thermal envelope), I believe the foam should be closed cell. That makes it a vapor barrier, so that humidity should not penetrate the foam. I believe that with open cell foam, the humidity can make its way through the foam and hit the cold roof deck and condense to water, and you end up with soggy foam held against the wood, causing moisture damage to the wood roof framing.

If it is closed cell foam, then the only concern I'm aware of would be gaps or voids with the coverage of the spray foam. Any gap in the vapor barrier provided by the foam would similarly allow humidity to reach the cold roof deck and condense. If it's a sufficiently large gap, you might see water dripping out, but I imagine that small gaps leading to void could allow the water to be trapped against the wood roof framing. I don't know what the best practice is to ensure that you don't have such gaps or voids, or to check for them after the installation is done.

Cheers, Wayne
 

pt5040

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So if the underside of the roof deck is sprayed, and if the attic is unventilated (as would be suggested by the attic being inside the thermal envelope), I believe the foam should be closed cell. That makes it a vapor barrier, so that humidity should not penetrate the foam. I believe that with open cell foam, the humidity can make its way through the foam and hit the cold roof deck and condense to water, and you end up with soggy foam held against the wood, causing moisture damage to the wood roof framing.

If it is closed cell foam, then the only concern I'm aware of would be gaps or voids with the coverage of the spray foam. Any gap in the vapor barrier provided by the foam would similarly allow humidity to reach the cold roof deck and condense. If it's a sufficiently large gap, you might see water dripping out, but I imagine that small gaps leading to void could allow the water to be trapped against the wood roof framing. I don't know what the best practice is to ensure that you don't have such gaps or voids, or to check for them after the installation is done.

Cheers, Wayne
Thank you very much for the detailed replies. I double checked the invoice and the foam used was indeed closed cell: Demilec HeatLok HFO Spray Foam Closed Cell - R30 average depth 4"......So it seems from what you and Fitter30 shared is that I simply have a situation change relative to my radiator days....The spray foam may be "forcing" the air escape to be concentrated through the windows instead of the entire surface of the home. Solutions are new windows or a window film. Second I need to manipulate the internal relative humidity more dynamically along with changes in exterior temp. Thanks again for your education and assistance.
 

wwhitney

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Solutions are new windows or a window film. Second I need to manipulate the internal relative humidity more dynamically along with changes in exterior temp.
To recap, you'll get condensation whenever air hits a surface cooler than the air's dew point.

So to avoid condensation, you first need to pick a layer that will be well air sealed, the air control layer. If your storm windows are well air sealed, that's your current choice; if they are not, you don't currently have an air control layer at your windows, as you said the wood windows are leaky.

Then you need to ensure that the indoor face of the air control surface will be warm enough to avoid condensation. You can do that be either lowering the indoor humidity based on the temperature of that surface (which will depend on the outdoor temperature); or improving the thermal separation between that surface and the outside, to raise that surface temperature; or some combination of the two.

If you make your storm windows the air control layer (leave the leaky wood windows as is), you'll either need to drastically lower the indoor relative humidity, or change the storm windows so the indoor face is warmer (maybe thermally broken double paned storm windows, which I assume exist on the market). If you make your wood windows the air control layer (via replacement or by adding a seasonal sealing film across them), then that should suffice, if as I understand you are not currently getting any condensation on the wood windows.

Cheers, Wayne
 

John Gayewski

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I hope your don't have Asphalt singles. If you do plan on replacing them about every ten years.
 

pt5040

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To recap, you'll get condensation whenever air hits a surface cooler than the air's dew point.

So to avoid condensation, you first need to pick a layer that will be well air sealed, the air control layer. If your storm windows are well air sealed, that's your current choice; if they are not, you don't currently have an air control layer at your windows, as you said the wood windows are leaky.

Then you need to ensure that the indoor face of the air control surface will be warm enough to avoid condensation. You can do that be either lowering the indoor humidity based on the temperature of that surface (which will depend on the outdoor temperature); or improving the thermal separation between that surface and the outside, to raise that surface temperature; or some combination of the two.

If you make your storm windows the air control layer (leave the leaky wood windows as is), you'll either need to drastically lower the indoor relative humidity, or change the storm windows so the indoor face is warmer (maybe thermally broken double paned storm windows, which I assume exist on the market). If you make your wood windows the air control layer (via replacement or by adding a seasonal sealing film across them), then that should suffice, if as I understand you are not currently getting any condensation on the wood windows.

Cheers, Wayne
Thank you again for all the help and guidance. Really, very informative.
 

pt5040

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I hope your don't have Asphalt singles. If you do plan on replacing them about every ten years.
Hi John - how are the roof shingles at play in this situation? I assume you are believe that my setting leads to reduced life of the shingle roof. Thank you for the help.
 

John Gayewski

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Yes. Asphalt singles need an air gap between the roof decking and any insulation. Any warranty on asphalt singles will be void without this gap. There are several products on the market which are stapled or placed between the roof decking and foam /insulation. This air gap should feed to your eves and ventilated soffit. This creates the conditions necessary for shingles to last 20 or more years.

My dad actually made this mistake on his house. It's an extremely large house with a lot of roof. It lasted ten years under the conditions you described above. Although I do think he was able to find a way to use the single manufacturers warranty. I don't think they checked or have a way to check. It's a cross your fingers situation.
 
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