Not all Green houses are created equal. Some are 'greener' than others. We like refer to this as 'shades of green'. Of our 4 new houses I would rank them like this:
Rowayton and California: Super- dark Green! Definitely LEED certifiable Gold or Platinum. (Rowayton is the only house actually getting certified and we are hovering on the Gold /Platinum line) Both are extremely energy efficient, use low carbon footprint materials and construction and make good use of alternatives in the form of Geothermal (ground source heat pump), Photo-voltaics (electrical solar panels) and Solar Thermal Panels (hot water solar panels)
Westport: Very Green. This house would probably get LEED Silver at least. Very energy efficient, mostly green materials and products, and use of geothermal.
Greenwich: Light Green. This is a solid energy efficient house- much better than your standard house construction - but not extreme in its green measures.
(btw: LEED is a rating system that registers how 'green' a building is. You can go to this website to learn more:USGBC website
So what is the difference. Well, as Mies van der Rohe said 'God is in the details'. Its all about individual components, very specific construction details and methods and degrees of performance in products such as insulation and windows. Today we will look at windows:
Below is a photo of the windows at the Greenwich house. They are quality Marvin windows. Nice.
You can see from their sticker (below) that they get a U-factor of .32, a Solar Heat Gain Coefficient of .26 and Visible Transmission of .45. The U-factor is like the R value of insulation. It tells us how energy efficient the window is. Solar Heat Gain Coefficient tells us how much of the sun's rays are getting though (You want the sun to get in if you are in a heating season and your house is designed for passive solar heat gain..you don't want the sun to get in because it fades the upholstery.) The Visibility refers to just that -how 'see through' the window is.
Films that are applied to make the window more efficient will lead to less visibility and less solar heat gain. So sometimes if we have designed a house to work in a passive solar way -yet still want it to be very energy efficient- we have to play a trade off game. Like maybe we decide to make the south facing windows less energy efficient than all the others so that we can get that winter sun in to heat up the house.
Here is a picture of the Westport house's windows:
They look very similar and are in fact made by the same parent company - Marvin Windows. These windows are - however- Marvin Integrity Windows. They get a U Factor of .29 or .30 depending on which window, a SHGC of .26 and VT of .46.
With U-factors, the smaller the number the better (the more efficient the windows). With this U Factor they are eligible to get the $1500 federal tax credit for energy efficient windows...but just barely.The u-factor needs to be .30 or less to apply. Next year I think they are lowering it to .28...I need to verify that. These windows meet Energy Star requirements (another sort of rating system.)
These windows are better performers than the 'normal' Marvins on the Old Greenwich house. Both are double paned, Low-E glass and filled with Argon gas. The Integrities are primarily fiberglass frames with wood veneer on the inside where as the normal Marvins are primarily wood frames with aluminum cladding on the outside. Fiberglass is more efficient than wood, wood is more efficient than metal.The difference in U factors comes from other tings too- like what the spacer bar between the glass is made of and how the windows are assembled.
The Integrities are less costly than the normal (O.G.)Marvins. So why not buy them? Well many people don't like fiberglass windows (Integrities or anyone's) when they get up close and personal(too thin or flimsier than the normal Marvins.) But honestly I think they have come a long way! I think they look pretty darn good up close and personal these days.
(And just as a note- my Minnesota architect friends think that the Integrities don't even cut it as energy efficient windows. They usually spec triple pane fiberglass windows with no muntins (you know those window grilles that everyone likes so much). Those windows achieve U factors of .20 or .22 or sometimes even as low as .15 or .16!! Pretty amazing. But in our neck of the woods we have a more mild climate and it is not really worth the cost to get windows that are THAT efficient. (Although if you really want to live 'off the grid' you should go for it.) People usually are concerned about the R.O.I. (return on investment) and don't see the value.
BUT speaking of triple pane windows- lets look at the Rowayton house:
These windows are triple pane Eagle windows with a wood frame and aluminum clad exterior. They get a U factor of .27. The best of our group. They achieve this due to the 2 air spaces between the 3 panes as well as having the low-E 4 glass. You can read about it here at Eagle Windows. These windows cost more than the Integrities but less than the normal Marvins and they give the benefits of having a nice wood window with high efficiency.
The performance of the window in the envelope also depends a lot on how they are installed and how those gaps around the windows are sealed. We'll get into that more later...
