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How Green Are Wood Doors?

Wood is a great option for an entry door, but its inherent insulating quality, look and renewable nature are not its best green feature. It's the fit that matters.

WOOD DOORS CONTINUE TO BE A FAVORITE at the high end of the custom home market. They're secure, renewable, convey warmth and status, and  have the "feel" that homewoners expect in entry doors. That "feel" quality may sound like an emotional perk, not a building science one. But they're actually on to something.

It's the fit that matters, more than the R-value.

A 1-inch wood door  has a U-value of about .64. Most people are more familiar with R-Values, so let's use those instead: A solid, 2-inch-thick wood door with a wood storm door has an R-value of about 4.17. That's about as good as you're ever going to get with a wood door. And keep in mind, it's still only about one fourth the R-value of a 2"x6" fiberglass insulated wall with no door in it. Walls trump doors and windows when it comes to energy efficiency. That's just the way buildings work.

But there's another factor to consider when evaluating the energy performance of any door: air leakage. If you accept the fact that in an older home, especially air leakage from doors, windows, walls, ceilings and pipes accounts for up to 50% of all heating/cooling loss, then the "fit" of a door takes on high importance.

In fact, according to neutralexistence.com, "An exterior door with a 1/8” gap between the door and the threshold is equivalent to a two square inch hole in your wall. By simply eliminating these gaps with door sweeps and weather stripping, you can potentially cut your your heating and cooling cost by 15%."

Add to that some additional energy loss for any missing or poorly fitted  weatherstripping, flimsiness or warpage in an old door, and the potential savings for replacing it with a new, prehung product gets even higher.

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Another issue is quality. Wood doors are typically assembled with wainscotting and fancy joint work. Assembly has to be top rate. Otherwise you could have air leakage through the door structure in coming years.

So what's the bottom line? Spend a little extra for a heavy, solid, wood door that has an equally well built, pre-weatherproofed jamb. Minimize glazings, and protect the door with a durable, tough finish that will keep joints healthy for decades to come.