Hey, everyone.

I am in the planning and early design stages of a new home using SIPs and with a very modern design approach (square form, a fair amount of windows).

I have three only-slightly related windows and glass questions.

1. I was originally set on doing the large window areas as glass block. I am not building on a vista lot, and I presumed the R-Value on glass block would be significantly higher than insulated windows and provide privacy without having to use blinds or curtains to prevent visibility into the interior. I then read recently that modern insulated windows have the same R-Value as glass block. Has anyone heard either anything to confirm or deny this?

2. I have since wanted to look into insulated windows, but still like the idea of the privacy that the glass block provides. Does anyone know of vendors or product lines that offer insulated windows that are not translucent but either frosted or otherwise altered to prevent visibility in while still allowing all the light into the spaces.

3. Does anyone know if there common building codes that require windows to be used as a means of egress from the house? If I choose glass block for windows, are there some minimum number of windows that would need to be kept openable for the purpose of egress?

Thanks for any advice, feedback.

- Peter B.

Actually, some windows have a higher R-Value(It's usually expressed as a U-Value). For Glass block, figure somewhere around R-2. Also, glass is a thermal conductor, and a glass block usually has conductivity between the outside and the inside.

I don't have a pointer, but I've seen windows that use electricity to change from clear to opaque.


Every bedroom must have an egress window. I have a client who tried to use a master bathroom window as the egress window for the Master BR. The building dept shot that idea down, and they had to find another wall in the master in which to create that window.

Go to PittsburghCorning.com for a lot on info about glass blocks. Here's their design data. LINK. There are several options for installing glass block windows, so you have an interesting info hunt ahead of you. There are acrylic blocks out there too. I think most, if not all, window mfrs can supply regular windows with obscure glass for bathrooms. But glass blocks rock, IMHO. I'm using one in the house I'm ready to build. Then there are outfits like Seattle Glass Block who sell preassembled block windows.

There are specific requirements for egress windows. If you can't find the info easily write back. I can quote it for you from the IRC.

Your questions belie the fact you are unfamiliar with these issues. I would recommend for your own benefit you do some research and learn what you can before you design, buy, or build, anything. Be careful talking to window sales people, especially the ones who sell replacement siding and windows. They aren't the biggest liars in the sales world, but I won't say where in the spectrum they are, IMO.

1. R-value on glass block, to my knowledge is not well established, but given the large air gap inside, the convection current probably make it a poor insulator. Insulated glass windows Energy Star qualified for your particular location woudl be a better choice. See the Efficient Window Collaborative.

2.   You can get energy star qualifed windows with obscure (frosted-there are other options also to achieve your goals here such as reeded or seeded that are more attractive than glass block or obscure) glass that will have the high insulation values and the privacy you wish.  See [b]custom windows[/b].

3.  all codes require a means of egress from each bedroom and at least one other means of egress in the rest of the home.  You will have to have an opening window in each bedroom of certain dimensions to meet this requirement.  The dimensions depend on what typreof window.  Make you get the company you quote these with to mark the egress windows in their quote.

Also someone mentioned glass that changes to opaque with a switch, this is very expensive and looks extremely grainy when in the clear mode.  Otherwise it performs like glass.  The retail charge for this glass will run arounf $150-$200 per square foot.

I have installed double glass block windows for one customer. On an ICF wall one set of glass blocks flush with the outside and another flush with the inside, which leaves 3-4 inches in-between the glass blocks. I think this would be very energy efficient and I plan on doing this on my own house.