Image Credit: Screen shot
Image Credit: Screen shot I got quite a surprise when I opened my new insulating blinds on the first cold morning to find a nice layer of ice on the inside of my single-glazed windows.
Image Credit: Carl Seville
More Green Building Curmudgeon
We had some serious cold weather down here in Georgia recently, and although it didn’t come close to Martin Holladay’s recent experiences in Vermont, the low temperatures were a bit of a shock and caused a lot of problems.
As the cold wave settled in, I was amused by a radio interview with a local plumber who said that the freezing wasn’t the problem, rather it was when everything thawed the pipes started leaking. He wrapped up by saying that he was going to have a very busy weekend and he was going to make a lot of money.
My plumbing survived
Having just reoccupied my almost finished renovation, I was a bit concerned about how it would fare in the deep freeze.
My house has an unconditioned and unvented crawl space with spray foam insulation on the underside of the first floor. I initially insulated the floor about eight years ago when the crawl space regularly filled up with water and sealing it was not feasible. As part of the renovation, I elected to retain the insulated floor rather than insulate the crawl space walls and remove floor insulation.
I use a dehumidifier in the summer, and as part of the renovation I was able to fill up the low spots so the area is now dry. I recently had all the plumbing pipes insulated with spay foam, a simpler process than installing separate pipe insulation.
I never checked the temperature in the crawl space during our cold spell, but no pipes froze, nor did my outside tankless water heater have any problems, so I think I’m safe for the next half century or so.
My single-glazed windows iced up
The house still has several single-glazed windows, and about half the walls remain uninsulated. That’s normally not much of a problem in this moderate climate, but 5 degrees sure doesn’t seem moderate (unless of course you live in Vermont).
I had installed cellular blinds on most of the windows just before moving back in, and while I realize they have insulative properties, they were primarily intended for privacy. I was somewhat amused to learn just how well they insulate. When I woke up on the first freezing morning, I opened them to see a fairly thick layer of ice on the inside of all the single-glazed windows. I had never seen even condensation on these windows in the past, so the ice was a bit of a surprise.
Part of the renovation project included comprehensive air sealing of the addition, and as much of the existing house as possible. (I have not done a blower-door test to compare the before and after numbers yet, but will report on that when it’s done). I surmise that the improved air sealing is retaining a fair amount of moisture inside the house (rather than letting it leak out through exfiltration as is common in the winter), keeping the relative humidity fairly high for the winter.
So, I had the very cold windows that created opportunities for condensation on the inside, and, the insulating blinds kept the space between them and windows below freezing, leading to the lovely layer of ice. I had not planned on installing storm windows, but now I am reconsidering that decision.
The house itself was never uncomfortable, although I tend to keep the temperature low. My minisplits did a great job of keeping it toasty, somehow, almost magically finding enough heat in the frigid outdoor air.
I do notice that the uninsulated walls tend to be a bit of a heat sink in very cold weather, as the plaster slowly acclimates to the wall cavity temperature. I chose not to insulate these walls as it would have required stripping interior plaster or exterior siding, neither of which would have any reasonable payback period. Sweatshirts and slippers are a much better investment for the few cold days we get here.
Southern winters are pretty short
So after single digits last week, I had the doors open yesterday when it was in the 60s and sunny. I feel fortunate that I made it through the cold snap with no frozen pipes, and the ice on the windows didn’t last long or cause any damage.
Having just moved back in a few days before, I was able to be there as the house got a good workout and fared quite well. I feel like I will be pretty comfortable for the foreseeable future.
With the exception of a few minor details, the interior is complete. The exterior carpentry is finished and ready for paint. Last on the list is a new driveway and landscaping. I’m hoping to have everything wrapped up in another month or two, depending on the weather.
I’m still working on some hot water distribution issues, and will write about them when I figure everything out.
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9 Comments
Frozen Pipes
One important house design element is NOT to install plumbing pipes on exterior facing walls. It's better to run the plumbing on interior walls in order to prevent freezing. Also, exterior air flow is the real enemy behind frozen pipes, so seal up those homes.
While homes are insulated based on the local code/climate zone. One has to remember that weather can go through extremes and cold spells in a Zone 3 climate are not only possible but most likely will continue to get worse. Any green builder worth his or her 2 cents will always insulate ABOVE CODE.
In Phoenix (Zone 2) they put the main water line on the exterior of the home, above ground, exposed to all the elements. Every winter people have to go outside and put blankets on the pipe when it gets below freezing. One winter it got into the mid 20's and thousands of pipes broke throughout the area, making plumbers very happy and wealthy. So it's not uncommon for a Zone4 climate to experience Zone5 weather or vice versa. Heat waves kill more people in the USA than cold winter weather.
Windows
It's also not uncommon to see ice forming on leaky double pane windows either. The below pic shows an Intus Window (triple pane) next to a double pane/double hung window on a -7F snowy day with -36F below zero wind chill.
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Windows don't much care about "wind chill"...
Wind chill is all about the amount of time it takes exposed human skin to freeze (frost bite), and nothing about the heat loss characteristics of windows.
Disruption of the boundary layer air film on the exterior pane by wind yields a small hit in performance for a double-pane window (and a bit more for a single-pane), but nothing like the implied difference between a -7F temp and a -36F wind chill temp.
Only those humans silly enough to bare a lot of skin during sub-zero weather need to pay attention to the wind chill number (and yes, -36F wind chills can freeze the tip of your nose or your exposed earlobes pretty quickly if you're not paying attention.)
In a zone 3 climate those single-digit temps can raise hell with the ventilated crawlspace concept if there's any wind, between frozen plumbing and frost forming on the conditioned space floor above the crawspace vent on the windward side. If there weren't already reason enough (and there IS, in a GA climate), I'd think just one round of this would be enough to convince folks to air seal, insulate and condition the crawl spaces.
To Dana Dorsett
I agree but while windchill does not effect inanimate objects, the increased wind speeds of a -7F mph wind chill vs a -36F mph wind chill can increase the leakage rates of a window, especially a double hung window. Blower door tests are done based on a 20mph wind hitting the home but increase that wind to 35mph or higher and the test results would change. Windows that are poorly sealed and that leak air at 20mph will leak even more air at 35mph. Air leakage in below freezing/below zero weather will cause moisture condensation to form, hence the frozen ice on the interior windows.
Response to Peter L
Peter,
You wrote, "Air leakage in below freezing/below zero weather will cause moisture condensation to form, hence the frozen ice on the interior windows."
Actually, this type of condensation (frost) has nothing to do with air leakage. The source of the moisture is the interior air. The glass window pane and the lower part of the sash frame are the coldest surfaces in the room, so that is where the condensation or ice will form. This phenomenon will occur even if there is zero air leakage -- as long as the interior air is warm and moist enough, and as long as the window glass and sash frame are cold enough.
The pipes and windows
About four years ago, Martin wrote story about Jeffrey Gordon's research on pipe bursts...
https://www.greenbuildingadvisor.com/blogs/dept/green-building-blog/jeffrey-gordons-paper-bursting-pipes
Since this is the time of the year... and its just been a few weeks since Martin's composite story of past winters and frozen pipes. Along with Carl's story... the pipe burst study is worth reading... It is a good reminder why good pipe insulation such as installed by Carl -- is useful even in a balmy Georgia climate.
In part 2 of the pipe burst study, Jeffrey included calculations on the BTU heat loss/hr with different winds blowing against the pipes. Thus my question to Dana and group -- ignoring windchill (a human effect value) -- why isn't the heat conduction loss from the center of the window significantly higher? Shouldn't the conduction off the glass have a similar effect as the conduction of heat from the copper pipe... (I understand there are different thermal properties).
As for the ice in the corners... everytime I've seen that... it has been thermal bridging problems in the frame... not the extra pane of glass. I've seen single pane windows in MT at -40F without frost on the inside (unheated garages-- small cheat)... but without pushing it.. I've also seen double pane windows vinyl windows that are sweat and frost free.
One hint -- look for melting on the outside pane of the window... that can be a tale tell sign just like the frost on the roof.
Response to Peter L comment #4
The effect of the wind on window performance is well under 10%, at 10 mph, and doesn't get any worse from there until the wind literally breaks the window. A little bit o' back of the napkin math:
The R-value of the exterior air film in calm air is about R0.17. A window with a U-factor of U0.35 has an R value of (1/U=) R2.86, and that includes the exterior air film. In a howling wind that exterior air film effectively goes to zero, leading to an R-value of(R2.86 - R0.17=) R 2.69, or a U-factor of (1/R2.69=) U0.37. That means it's losing about (U0.37/U0.35 = ) 1.06 as much heat as in calm air, a 6% increase in heat loss vs. calm air.
At.,say, -5F and a 40mph wind, you get a wind chill of -36F(see: http://www.nws.noaa.gov/om/windchill/ ). But the increased heat loss of the window in a 70F room from that same 40mph wind is roughly 3% more, the equivalent of a 3% greater delta in interior and exterior temperatures. So, given that 1.06 x a delta of 75F is about 79F, which implies a "window chill" factor of (70F-79F= ) -9F when it's -5F out in a howling wind.
In better performance lower-U windows the loss of the exterior air film has an even less of an effect, since the air film comprises an even lower fraction of the R-value of the window assembly.
The difference between -9F "window chill" and a -36F "wind chill" is huge, and that's why using human-skin wind chill factor figures has no real relevance in a discussion about building-component heat losses.
Copper is a refractory material of EXTREME thermal conductivity.
The bottom line is, glass and copper aren't very similar at all.
Both aluminum and copper have a thermal conductivity more than two order of magnitude higher than glass, and several orders of magnitude higher than the argon or air between panes of sealed glass. (See: http://hyperphysics.phy-astr.gsu.edu/hbase/tables/thrcn.html ) Sealed windows typically have aluminum separating the panes, forming a thin but highly conductive thermal bridge.
If you're not seeing frost on single-pane glass at -40F outdoor temps it means your ventilation rates are high enough to keep the interior dew point extremely low, which would be pretty likely in a garage, that doesn't have interior moisture sources such as showering/cooking/breathing humans. An occupied-conditioned house really IS different.
Copper is different
Thanks Dana, I knew the answer - a little bit of a setup and yes garage was a cheat (unheated separate)... but thought it would be useful for others to really understand. I have seen insulated glass windows installed into unheated (and mostly vacant) building...
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