Glass Block or Insulated Replacement Window
December 19, 2013 7:44 PM   Subscribe

So I have been working on my house and making it energy efficient. It is now time to replace the basement windows in my split level. One double wide window needs to be replaced with one that opens to meet code, but the other three single wide windows do not. Would I be better installing glass blocks in those three, not vented, or installing either a picture, slider, or another type of insulated vinyl replacement window? If I should do a replacement window, which type should I use?

The window openings are in the foundation. The bottom and sides abut cement block with the top of the opening being painted, pressure treated wood. I am looking to get the best seal and insulation value for everything. Energy efficiency trumps everything for me. I will be doing all of the work myself, but can get assistance as needed if a two person job would be significantly easier. I have very high carpentry skills so nothing really scares me. Rough openings for the three needing replacement are 35 inches wide by 22.5 inches high. I have enough space to install 4 inch deep glass blocks or any other type of window. Please let me know what you think, I have been thinking this over for more than a month and have gone crazy looking at numbers and options.
posted by Nackt to Home & Garden (6 answers total) 1 user marked this as a favorite
If energy efficiency is the trump card for you, you'll go with regular windows over glass block.

Glass block specs here (pdf) - look at the "U-value" column (R-value works too, R and U are really the inverse of each other, so you're looking for a higher R-value or a lower U-value. Insulation is typically specified in R, windows generally U, but you'll get listings for both sometimes). Pittsburgh Corning is the big glass block manufacturer, so those numbers are probably standard, and their engergy-efficient model gets a .45 U-value (2.22 R-value).

Milgard is one of the larger manufacturers of replacement windows, and specs for one of their vinyl products can be found here (on the tabbed thing down the page, click on the "specs" tab). This seems like just their base model double hung window, and it has a U-value of .35 (R-value 2.85).
posted by LionIndex at 8:12 PM on December 19, 2013

Best answer: Additionally, you can increase the U-value of the window further by using a casement or awning instead of double-hung (is that what you mean by double-wide?) for a U-value of .31. Milgard gives a range, the best U-value may be based on getting triple glazing or exotic coatings, but even their worst product beats glass block.
posted by LionIndex at 8:17 PM on December 19, 2013

You want windows if you want the light, non operable if you don't need the ventilation. If you don't need either, then insulation is best.

Windows come in a very wide range of insulative values - your budget is the limit here. Any good window manufacturer can provide U-values for their products. Depending on the rest of the house, you may be better off spending your money elsewhere though.
posted by ssg at 9:52 PM on December 19, 2013

Response by poster: By double wide, I meant that I will be getting a 70 inch x 22.5 inch sliding window. That will be my emergency exit.

Light is not too much of an issue since the other windows open up beneath the deck on the back, the extra wide side window has a nice view of my side lawn. I am looking to close them up and do not need the ventilation.

So far, it looks like a vinyl picture window will get me what I want.
posted by Nackt at 3:59 AM on December 20, 2013

We had the same concern in our basement and went with wood Marvin Awning Windows. The actual windows where the Ultimate Push Out Awning Window. They are very energy efficient and do give you the option of opening the windows for a little fresh air which we found preferable to glass blocks.
posted by lstanley at 9:24 AM on December 20, 2013

If the windows are under a deck, they aren't really doing anything for you. Close the ROs off with plywood and insulate them.
posted by ssg at 9:52 AM on December 20, 2013

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