Can you recommend suppliers of low U-value solid wood windows?

In the development of low U-value windows, U.S. manufacturers have gone to slim frames and synthetic materials, leaving the development of low U-value wood windows mainly to their European colleagues.

Since the testing cycles in Europe are not the same as in the U.S., we cannot say precisely how much of an edge the European windows have, but they tend to

• get better U-values while retaining higher SHGC and
• use natural materials rather than fiberglass frames.

Window manufacturers

Paradigm, Serious Windows and Thermotech are some of the best U.S.-made windows available.

But if you want high-performing wood windows, you will probably need to look at European manufacturers that sell in the U.S.

• T and T Window, Optiwin, Quantum Builders and Bieber USA come to mind, as well as the much lower-priced breezepanel.com (note that I own a 50% share in Breezepanel).
• These are all high performing and very long lasting windows; most are pricey, but I think still a good value for what you get.

A good and impartial discussion of many of these windows was published in Fine Homebuilding Aug/Sept 2010, which you could check out at your local library.

European windows

I am clearly partial to European windows, as you can see, and have advocated this position on Green Home Guide for years.

European, and notably Swiss, German and Austrian building standards have pushed their window manufacturers for decades to produce higher-performing windows.

• This has resulted not only in more efficient frames, but also in better glass.
• European sourced triple glass measures up to 1 3/4" from inside face to outside face, while most American triple glass measures only one inch.
• Sadly, the glass is actually in many cases made by the same manufacturer -- but they will not sell the high-performing versions in the U.S.