SawHorse.net
SawHorse.net
  • Hometalker
  • Atlanta, GA
Asked on Jul 27, 2012

Building Science Geeks- I need help with a window problem

SawHorse.netPaul MWoodbridge Environmental Tiptophouse.com
+7

Answered

Yes- I am a "geek" as well. Here is the issue:
I just got hired on a complicated whole house renovation where the house has structure and building performance issues. I have most everything worked out except for what to do with some misordered windows.
The client had already ordered the windows before they met me and once I got the specifications on the windows, the had already been manufactured so there is no going back. Here is the issue- they were sold triple paned windows designed for cold climate conditions. The u-value is .12 which is great however the Solar Heat Gain Coefficient is .5. GA code is .5 for u and .3 for the SHGC.
I gave the client my 20 cents, however I cannot force them to choose my options.
What would you all recommend and I can let you know some of the things that I recommended to them if they were to keep these windows?
10 answers
  • The .3 SHGC is that for the entire window? Or the Glazing along. Typically numbers that low are including the frame in the formula. I am working on an answer for you.

  • With a .5 or 50% of the heat gain coming though the window. That is a good thing in colder climates to help the house stay warmer in winter months. To lower that number to .3, although your really not, you can construct some sort of shading to lower the amount of sun exposure in the form of overhangs or install a film on the surface of the glass to lower the sun exposure of the glazing, thus making the window perform better. However will not change the Value based upon the manufactures rating and with a film that may not work may also void the warranty of the window. Plus the code office may not recognize the shading as the window still has the same rating regardless of what you do. The manufacture of the window would have to re-rate the SHGC with the film installed, provide a document to meet the local code requirement in order for it to be approved. Or get the code official to wave the requirements if the overhang was increased or the windows were facing a more northern /eastern direction. Even if you were successful in lowering the amount of sun exposure of the glazing the fact remains the window is still rated at .5. My suggestion is one or two things can be done. Contact the manufacture to see what if anything can be done to effectively (if at all) lower the rating to meet the current code that would not effect the warranty of the window unit. And that the code official would approve of. Or simply explain to the client there is nothing that can be done with these windows to meet the current code requirements. How many square feet of window are you talking about?

  • SawHorse.net
    on Jul 27, 2012

    I agree- these were designed for Germany or the NE US- not for GA. We need to block the sun since we have a good number of cooling degree days.

  • SawHorse.net
    on Jul 27, 2012

    Right now the best option that I can think of beside replacing all of the glass is to install exterior mounted solar screens since the windows tilt inward.

  • Issue is however, Depending upon the solar filtering within the windows themselves. Sometimes that has a way of canceling out the benefits of both filtering systems. But will the township allow this to bring the window up to code?

  • SawHorse.net
    on Jul 27, 2012

    The SHGC on the shades is about .15 so we should be good regardless of the SHGC on the windows. We still have to get them approved through the HOA, which should not be an issue since they are on motors and are retractable.

  • Check this product out. We have local installer doing this brand. Clients love it and have noticed a big difference in their comfort level as well as utility costs. Bob http://www.enerlogicfilm.com/en/Default.aspx http://www.vista-films.com/en/default.aspx

  • Paul M
    on Jul 28, 2012

    There are window films available that will cut the solar heat gain of those windows but I am not sure how it will affect the U-value. I do know that we put some of that film on some old double hung windows years back and the performance of those windows substantially improved in summer and winter after that. I had even considered doing the whole house once we found out how much better the windows performed, but we moved before we could get around to that.

  • SawHorse.net
    on Jul 28, 2012

    I also just found out that Marvin Integrity offers triple paned windows. I am headed to their plant next week and will share some pictures with the hometalk community.

  • SawHorse.net
    on Jul 28, 2012

    I will check out these films Bob- thanks for the suggestion.

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