The National Trust for Historic Preservation has quietly been operating its Preservation Green Lab for a few years now and we’re finally starting to see quantifiable data verifying what preservationists have long believed – replacement windows are not the best option for home weatherization measures. With the help of the Cascadia Green Building Council and Seattle-based Ecotope, the Green Lab has issued this new report which makes it clear that storm windows combined with cellular shades is probably the best solution to weatherizing windows in our older and historic homes.

Portland was one of the cities reflected in this study, so the report should be seen as even more relevant to the owners of the thousands of Portland area homes built with traditional wood windows – most prior to World War II.

So what are a few of the takeaways from this important study?

1. Retrofitting your old windows can give you energy performance similar to that of replacement windows.

2. Nearly all retrofit measures provide a better return on investment than replacement windows.

3. The average initial cost for replacement windows in Portland is roughly twice that of a combination of exterior storm windows and insulated cellular shades. When you combine that with the fact that the average energy savings between these two types of weatherization measures is a mere 2-3 percentage points, you can see why replacement windows are, by far, not the best option.

You can read more about the report on the National Trust’s website here.

One final note for owners of designated historic homes:  Interior weatherization measures like installing insulated cellular shades or interior window panels, probably won’t trigger those historic design review fees that many in Portland are (rightfully) up in arms about.  So not only can you save money and energy, you might also save the hassle and cost of that process.