Oak and Steel

Understanding Window Energy Ratings

Buying new windows for your home can be expensive and intimidating.   Understanding the Energy Performance Ratings can make the process less painful while adding comfort and energy savings.  There are four main measurements to look for when shopping for new windows: U-value, solar heat gain coefficient, visible transmittance, and air leakage.  But what do these numbers mean?

U-Value is a measurement of the heat flow through the window.  It can be compared to the R-value (resistance) in insulation though it is the opposite.  A lower U-value means less heat is transmitted through the window.  U-value = 1/R-value.  A window with a U-value of 0.33 would have a R-value of 3.  A lower number provides more insulation.

Solar Heat Gain Coefficient is the ratio of solar heat gained by the window compared the amount of solar energy hitting the window's surface.  The measurement is a number between 1 and 0.  A SHGC of 1 indicates 100 percent solar gain while 0 indicates no solar gain.  It is best to develop a window strategy with different SHGC for different windows.  West-facing should be avoid but when they are used,  the SHGC should be very low to avoid over heating the home in the afternoon.  South-facing windows should have a high SHGC to allow low angle winter sunlight in to heat the home passively.

Visible Transmittance is the measure of how much light the window transmits.  The number is also between 0 and 1.  The higher the number, the more light allowed to pass through the window.

Air Leakage is the measure of cubic feet of air leakage per minute per square foot of window.  Windows with air leakage less than 0.3 cfm/ft2 is recommended.  Casement windows generally preform better than sliding windows in air leakage while fixed windows perform the best.

"Air leakage siphons about half of an average home's heating and cooling energy to the outdoors each year.  Air leakage through windows is responsible for much of this loss."  -Paul Fisette Energy-Efficient Building

Spring Has Sprung

When pruning flowering trees in spring, bring some of the branches inside and place in water.  The heat in your home with force the branches to bloom.  An easy way to celebrate the changing of seasons and bring beauty inside.

Shipping Container Conversions

Sustainable Residential Remodeling - Sonoma

Simple Savings - Window Treatments

Ideally after your retrofit is complete, your house will have dual paned windows with UV filtering glass in the right places.  Window replacement is quite expensive and is generally the last step in a phased remodel.  The whole low hanging fruit and bang for your buck idea.  In the meantime, there are first steps to help you stay comfortable and save energy.

Well designed window treatments can go a long way to cutting your energy and saving you money.  Heat moves to cold, so depending on the situation or time of year, you will use different strategies.  Thermal lined drapes or roman shades are best for keeping the heat in during the winter.  Open them up during the day to let the sun warm the room and close them tight after the sun goes down.  There are special thermal lining products on the market and an additional flannel interlining can increase the insulation.  In the summer, it is best to keep the sunlight off of the window rather than block it once it in inside.  Outdoor solar roller shades, permanent overhangs, or deciduous plants can help block the summer heat when well designed.