Cutting Back on Glass

glass buildings

“How do we go about designing buildings today for tomorrow’s weather? As the world warms and extreme weather becomes more common, sustainable architecture is likely to mean one major casualty: glass. For decades glass has been everywhere, even in so-called “modern” or “sustainable” architecture such as London’s Gherkin. However in energy terms glass is extremely inefficient – it does little but leak heat on cold winter nights and turn buildings into greenhouses on summer days.”

“For example, the U-value (a measure of how much heat is lost through a given thickness) of triple glazing is around 1.0. However a simple cavity brick wall with a little bit of insulation in it is 0.35 – that is, three times lower – whereas well-insulated wall will have a U-value of just 0.1. So each metre square of glass, even if it is triple glazed, loses ten times as much heat as a wall. Cutting back on glass would be an easy win. Windows need to be sized, not glorified, and sized for a purpose: the view, or to provide natural light or air. Windows also need to be shaded. Many would argue that we need to re-invent the window, or the building. We need to build buildings with windows, rather than buildings that are one big window.”

Read more: Climate change means we can’t keep living (and working) in glass houses. Via Lloyd Alter.

The Kume Shade: DIY Insulating Curtain

kume insulating curtains

The Kume curtain is a simple and inexpensive home-made insulating curtain that can help save money, keep our homes cozier and be kinder to the environment.

The Kume is a roll-up curtain that is composed of four distinct layers.

  • A front panel which acts as the first layer and seals the perimeter of the window opening when the curtain is closed
  • A moisture barrier which prevents indoor humidity from reaching the window and condensing on the cold glass and window frame
  • Wooden battens which maintain the fabric stretched out and thereby ensure that the curtain fits tightly against both sides of the window opening (the battens also create air pockets which further reduce heat losses through the curtain)
  • A back panel which acts as the final layer of insulation and helps seal the perimeter of the window opening when the curtain is closed.

kume insulating curtain insideWhy is a Kume curtain so effective at reducing heat loss?

  • Still air is one of the best insulators found in nature, and the Kume curtain contains a lot of it. First, between the fibers of the thick polar fleece that is used to make the curtain, and second inside the thin spaces that are created between the front and back panels by the battens.
  • When closed, the Kume curtain fits tightly against the top, bottom and sides of the window opening. By doing so it traps a layer of insulating air between the glass and the curtain, and prevents the cold air that forms against the glass from seeping into the room.
  • A Kume curtain basically works just like a good down jacket on a cold winter day. The air that is trapped in the thick layer of down creates an effective insulating layer, and the tight fit of the jacket around your waist, neck and wrists keeps your body heat in, rather than letting it leak out into the cold environment.

See and read more (including construction plans) at Kume Insulating Curtains. Via BuilditSolar. Thanks to Frank Van Gieson.

Bubble Wrap Window Insulation

bubble wrap window insulation

“This is a simple technique for insulating windows with bubble wrap packing material. Bubble wrap is often used to insulate greenhouse windows in the winter, but it also seems to work fine for windows in the house. The view through the bubble wrapped window is fuzzy, so don’t use it on windows where you need a clear view. But, it does let plenty of light through.”

“The bubble wrap has a short payback in cold climates. About 2 months for single glazed windows, and half a heating season for double glazed windows. For an 7000 degree day climate (northern US), and single glazed windows, the bubble wrap increases the R value from about R1 to about R2. This cuts the heat loss from the window in half.” Read more.

Retrofit Measures Can Achieve Energy Savings Comparable to New Replacement Windows

window retrofit strategies

“Growing interest in improving the energy efficiency of residential buildings inevitably raises questions about what to do with existing windows. Homeowners often assume that replacing older, leaky windows is the only way to save energy, an assumption actively promulgated and reinforced by companies selling replacement windows and by the availability of federal tax incentives for installing new, high performance windows.”

“The confusion is often compounded by a lack of easily accessible information on the range of window improvement options available and the ability of these options to provide meaningful energy savings.”

“This study examines multiple window improvement options, comparing the relative energy, carbon, and cost savings of various choices across multiple climate regions. Results of this analysis demonstrate that a number of existing window retrofit strategies come very close to the energy performance of high-performance replacement windows at a fraction of the cost.”

Saving Windows, Saving Money: Evaluating the Energy Performance of Window Retrofit and Replacement“, Preservation Green Lab, 2012. Via Old House Web.