Your windows "freeze up" because the interior temperature of the window is below freezing. As you explain it in your post it isn't just the glass but the sash and frame as well that have ice on them.

The question is not so much "should" they freeze up, as it is "why do they" freeze up.

Since you have done your research, you already know that condensation forms on an object when the temperature of that object is below the dew point temperature of the air surrounding it; and that relative humidity is a comparison of the actual vapor density versus the saturation vapor density at a particular temperature; and that dew point is 100% vapor saturation or 100% relative humidity at a particular temperature.

You noted that your home was at 30% RH when you were having icing problems on your windows. Keeping in mind that 30% RH at 55 is a good bit different that 30% RH at 85°, what does 30% RH possibly mean in your situation?

Well, at 55° you would need a little less than 3-1/2 grams of moisture per cubic meter (g/m^3) of air to reach 30% RH; while at 85° you would need 9 g/m^3 to achieve 30% RH - almost three times as much water in the air at a 30-degree difference to maintain the same RH. If you kept your home at 70°, then 30% RH equals 5.5 g/m^3 moisture. So why is any of that important?

The difference is in the dew point. Dew point is based on the level of moisture in the air and is independent of the temperature of the air at a given moisture level. In other words, if you have 5.5 g/m^3 moisture you have a dew point temperature of 35° F regardless of the temperature you keep the air in your home. BUT, the RH changes based on the temp in your home. So, at 5.5 g/m^3 moisture, you have a RH of 19% at 85° and an RH of almost 50% at 55°.

If you keep the air in your home at 74° and 30% RH during the winter, you have a dew point of 38.5°. So anything in your home that is at 38° will likely develop condensation.

If you keep the air in your home at 66° and 30% RH during the winter, then you have a dew point of 31° - which happens to be below the freezing temperature of water so that you not only have condensation forming, but now you also have the added possibility of ice forming as well.

Your windows donÂt have a LowE coating which is unfortunate because in the cold winter months LowE coatings work to help keep the warmer air that is inside your home  inside  by raising the U-factor of the IGU (Insulating Glass Unit) which lowers conductive heat loss, and they do it by blocking radiant heat loss thru the glass unit as well. LowE coatings work as advertised. And to answer your last question, they work very well on the north side of your home  the level of sunshine is immaterial in that situation.

From your post it sounds to me like you have A LOT of condensation. You have water running down the windows and covering the sash/frame as well which then freezes causing your windows to freeze shut.

A dual pane window without LowE coating is going to have a center-of-glass temperature of about 43° when the outside temp is 0° and the inside temp is 70°. This does not take into account, any outside winds, any air movement in the home that may contact the glass surfaces, or any direct solar gain. The center-of-glass is normally the warmest part of your window. The edges are going to be cooler. Also, you didnÂt mention what kind of windows that you have  double hung, casement, sliders, etc. That can make a big difference in performance, particularly if they were not installed correctly, but the level of air leakage can vary among different styles of windows as well. Air leakage can be important.

Your windows are forming ice. That means that the surface temperature of the unit is below 32°. The 5.5 g/m^3 of moisture in your air that you would have at 70° and 30% RH equals about 110% RH at 32° - which will result condensation and potential ice forming on the window surfaces.

Nature doesnÂt like things out of balance. Nature tries to put things into balance.

As the air around your windows cools, it releases moisture as condensation, thus the air near the window surface is going to be both cooler and dryer than the rest of the room (as an aside, many people believe that heating air dries it. This is not true. Warming air does lower RH, so that we perceive the air as being drier as long as the moisture level has not changed). Since nature doesnÂt like the idea of the air near your windows to be either colder or dryer than the air in the rest of the room, nature responds by trying to equalize the temperature and moisture level everywhere in the room  including next to the windows  you then develop convection currents that move warm air over the window surface and cooler air into the rest of the room. That warm air is carrying that 5.5 g/m^3 into the colder area around your windows and that moisture is condensing on the window surfaces and cooler and drier air is circulating back into the room. And welcome to air conditioning 101. And, if there are any air leaks in your windows, warm air is going out to be replaced by colder air and the process is exacerbated.

One way that you can help your windows is by using fans to blow warm air across the surface of the windows. I know that this sounds a bit counter intuitive based on what I typed in the last paragraph, but warm air movement over the windows will warm the surfaces and hopefully raise the temperature to somewhere above the dew point of the units.

Another is to check for leaks. Improper initial installation can result in air leaks between the frame and the wall and between the frame and the sash. Even tiny leaks can be a factor. I might also carefully remove a piece of edge trim and see if the contractor insulated the space between the wall framing and the window frame. No insulation, inadequate insulation, or improper insulation in that area can be critical to a windowÂs performance.

We have glass that freezes, too. Ours are Pella and the reason for the excessive condensation is that Pella sold our development builder single fixed outer pane with removeable inner glass casement windows. We live in Zone 5, which requires double fixed pane with argon gas between. After five years we are still working at getting this corrected.

WOW thanks oberon that is a lot more detail then I've found anywhere else. So out of all that I've picked out two statements that really fit me and would for the most part explaining the freezing.

"If you keep the air in your home at 66° and 30% RH during the winter, then you have a dew point of 31° - which happens to be below the freezing temperature of water so that you not only have condensation forming, but now you also have the added possibility of ice forming as well. "

So keeping our house colder for the most part accelerates the freezing since it misses the dewpoint that is above freezing it almost goes directly from air to ice.

"A dual pane window without LowE coating is going to have a center-of-glass temperature of about 43° when the outside temp is 0° and the inside temp is 70°."

So since we don't keep our house at 70 it's more like 67 that's going to lower the inside temp of the window thus causing it to reach the dew point faster which is already close to the freezing point.

This is great information but bad news. So the next question is to figure out how to get a happy medium between indoor temp and humidity with out the nose bleeds and with out so much water running off our windows.

I've heard that you're not suppose to put storm windows on vinyl because it can build up heat and warp them but can that happen on north windows where they get no sun? Also if we would do that plastic over them from the inside would that do the same as storm windows? We thought about doing a storm like window but with vents for more of an air breaker but have the vents to keep it from getting to hot. Thoughts on that?

I knew I shouldn't of let the wife put in so many windows when we built.

Sorry I forgot to mention that we have double hung which we just found out are much worse the any other ones. How do they still get the energy star rating I have no clue. I think they said the casements were the best. Maybe we will have to upgrade to triple pain casements.

Double hungs can allow more air leakage than other window styles. But, there are double hungs that are very tight and that do stop airflow quite well.

I would suggest that the first step is to carefully pull a piece of side trim from one of the windows and see what the manufacturer used for insulation between the window and the wall framing. Or to see if there is insulation in that gap.

I might also measure a couple of the windows corner to corner to check on the squareness of the installation and also check the level of the units.

Again, since they are clear glass, they don't have the best possible glass-insulation value, but from your descriptions it does sound like there could be an air leakage factor as well.

I might also suggest holding a flame near the window when you have a steady wind to see if you might find leakage somewhere. Air leakage is also often a sign of poor installation and in two year old windows I would probably think of that as a possible factor as well.

The simplest assessment might be to place a hygrometer next to the window/s and measure the humidity level. If it is 30% in the middle of a large room, it wouldn't be unusual to have levels near 70% next to a cold glass area of a window. If this is the case, be thankful that you purchased a well sealed window, and then install an air exchanger in the attic.

Our home was built in 2007 and is a two story with fir/metal clad windows. The interior surfaces are varnished. The manufacturer is All Weather Windows. Our home is in Edmonton AB...very cold winters. The windows are dual glazed with low e, argon filled. For whatever reason, the windows (on the second floor only!!!) freeze shut in the winter. We manage our humidity levels quite well and don't get much moisture buildup on the glass. It's particularly odd that only the second floor windows freeze shut. Anyone know what's going on here?

My first thought would be moisture levels on the upper floors vs. the lower floors.

Use a psychrometer to see what the humidity levels are upstairs vs. downstairs when the air is more static.

Moisture levels have been rigorously checked. Temperature and humidity are consistent between upper and lower floors. I wondered about a "stack effect" occurring but a Blower Door Test came with acceptable results (meaning no significant air loss causing air pressure to drive to 2nd floor). Window manufacturer has no suggestions.

Any other comments?

What is the construction of the home?

Does the lower floor have more thermal mass, exposure, insulation, etc?

What did the IR scan indicate?

Custom built 2007, wood frame, r-values as per northern climate spec. Same construction main floor and 2nd level. Blower door test identified no significant leakage. Didn't do an IR scan - good idea though.

My only theory so far is that the air pressure (stack effect) is greater than window seal capability. No cold air coming from outside but interior air pressure is somehow pushing to outside. Stack effect would drive pressure to second level but, then, this doesn't jive with the blower door test which indicated the house is air tight. Perhaps the test is representative of air in only and air out (stack effect) is higher pressure than blower door test? Hmm.

Thank you for your thoughts so far.

Insulation levels in attic at the eaves?

Stack pressures inside the home will drive exfiltration to outside the home via top plates, can lights, windows, etc.

That does not help answer the frozen answer.

How big are the eaves? Are you getting direct sunlight on the upper windows?

Is there a danger of the crank mechanism freezing open during the winter nights in below zero temperature ?

Is there a danger of the crank mechanism freezing open during the winter nights in below zero temperature ?

Is there a danger of the crank mechanism freezing open during the winter nights in below zero temperature ?

No there is not....