Seal failure.

One thing I don't like about casement windows is that the outside glass surface sits proud or outside the plane of your wall, which has the effect of making the glass surface colder than the glass surface of other types of windows in the same conditions.

Also when the window sits deeper or further out from the plane of the inside walls, it's harder for warmer inside air to "wash" the window and warm the glass.

Add to that the internal screen which, in my opinion, causes casements to be more prone to inside condensation when it's really cold outside.

First thing, lose the inside screen when it's cold out. That should help. Second if you have curtains or shades that cover the windows at night, leave them open as much as possible when it's cold out. You need to get warmer air flowing over the glass, something the screen or any other coverings will block.

Basically, the glass is COLD which is pretty obvious given the ice formation resulting from the glass surface temperature being below freezing. IG seal failure isn't going to cause that, but missing or worn weather stripping or the window not closing tight might be a contributing factor, or might not.

Relative humidity is the percentage of moisture in your air compared to the amount of moisture the air can hold at a given temperature. Raise the temperature without changing the moisture level and rh goes down. Lower the air temperature without changing the moisture level and rh goes up. Basic physics.

Dew point is defined as saturation vapor density or 100% relative humidity. Dew point temperature is 100% dependent on the amount of moisture in your air and is 100% independent of the temperature of the air.

If the glass temperature is above the dew point temperature - dry windows. If the glass temperature is below the dew point temperature - wet windows. Your glass temperature is way below the dew point temperature.

You can stop condensation by either raising the glass temperature above the dew point, or lowering the dew point to a level below the glass temperature by removing moisture from the air. That's how you eliminate window condensation.

Your glass is below 32°F, we know that because of the ice formation on the glass. You say that your relative humidity is 28%. Two questions - first, where was the reading taken? Second, what is the temperature in your home?

For an example (I am mixing metric and imperial because it’s easier to calculate in metric but giving temperatures in F is easier for non-metric folks),

consider a home at 65°F with a relative humidity reading of 40%. In this scenario there are 6.25 grams of water in a cubic meter of air in the home which equates to a dew point temperature of 38°F.

If the window glass is less than 38°F then condensation on the glass is likely to occur. Since it appears that the Rh is too high resulting in wet windows, what if we lower the rh by raising the air temp to 75°F resulting in lowering the rh to 29%. Will lowering rh fix the problem?

Unfortunately despite lowering rh reading of 29%, the windows will still have condensation build up because lowering Rh by raising air temperature did nothing to lower the dew point which is still 38°. Changing Rh to eliminate condensation only works if excess moisture in the air is removed. So in your case you may have an rh reading of 28%, but clearly and unfortunately your glass temperature is way too cold for the level you do have.

Your fix is not to lower moisture, your fix is to warm up the glass. To repeat, first lose the screens and don't close curtains or blinds if you have them. Second, use a small fan or even space heater to warm up the glass when it gets very cold so that the dew point is well above freezing.

Do you know if you have LowE coated glass? That makes a HUGE difference.

Again, IG or glass seal failure does not result in interior (that you can touch, if between the lites is a totally different story) condensation when it gets cold out. Bad or missing weatherstripping or a window that doesn't close tight might.

I suspect that you live someplace where it's usually relatively warm even in winter based on your comment about the cold, so it is entirely possible that your problem will clear up as soon as the temperatures return to something approaching normal for you.

@oberon476, I have implemented many of the things you have suggested already, and still the ice in the photo above appears.

In my research, it appears that ice can also form on the inside of the window if the panes were not installed properly or the seal has failed (this article and many others say as much:https://www.ecolinewindows.ca/ice-on-windows/)

What tests are available to determine whether the issue is due to a poor installation or failing seal vs. a humidity issue? We have been very careful with our indoor humidity, have not closed the blinds all the way, etc., and we still have a problem and that is why I wonder about the seal.

If you wipe the water and ice off of the inside of the glass is there water and ice between the panes of glass?

@oberon476, we have the issue on many of the windows throughout the house, to varying degrees. The window in the photo is in our master bedroom. We run a big fan in that bedroom all night long, so there is good air circulation. We also have this issue in rooms that are relatively dry, such as our sunroom, and in my office, although there we did not have as much ice or condensation as the bedroom.

In our master bath we run the fan for a good 1-2 hours after we have showers to reduce the humidity.

I just talked with my parents who live in our area, and they said they had zero issues like what we have experienced in this last cold streak. Maybe a small amount of condensation on their bathroom window, but certainly no ice.

These windows are a nationally-known brand based in Minnesota.

What is the IG seal? Is that Inert Gas?

I don't know of anybody who lives in Minnesota (like we do) who has to go out of their way to blow fans, run special heaters on their windows, or do extensive mitigations to prevent issues like this. These were very expensive windows installed in 2015, and it seems crazy that we would have to practically hire a curator to take care of our windows to prevent issues. Only time I've had problems like this was in college with cheap single-pane vinyl windows.

I, misread and thought this was between the glass.

They appear to be leaking air at the bottom, are the windows locked? The window spacer can be a weak point when temps get that cold.

Bayport or Warroad? And I take back my comment about relatively warm...

The IGU's in your windows were made by Cardinal. If you are unfamiliar with them, they are headquartered in Eden Prairie and are probably the largest residential IG manufacturer in the world. I am biased but I truly believe that they make the best IG units available.

Are you in the cities?

You are right that you shouldn't have to practically hire a curator to take care of our windows to prevent issues,

Have you had issues in previous years or is this something new this year?

Can you send me a private message?