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What Type Of Wood
For Exterior Window Trim?

I am installing new windows on my house. What is the best type of type of wood to use for the exterior trim? I have chosen to trim my windows with some type of 1x4. My house is 20 years old and the siding is painted cedar 1 X 6 planks, it's in good shape. Should I use cedar, hemlock, pine, pressure treated something, etc? 

Steve K.

If the siding on your house is rough-sawn cedar, then my personal preference would be to use similar rough-sawn cedar 1x4 for trim. Matching the texture would be my highest priority. Rough-sawn lumber is available at many lumber yards. Over the past few years I have seen rough-sawn cedar stocked occasionally at either Home Depot or Lowes.

If the siding is smooth, then you could use any type of lumber. Pressure-treated Southern Yellow Pine (almost all that treated stuff is SYP) is not everyone's favorite for trim because sometimes it warps badly. But if held with enough nails (and long enough nails, 1 inch penetration into the framing) it should stay in place.

You could also use any clear and straight softwood, pine, spruce, fir, etc. For many people the price of the wood drives their decision. But any wood with knots will have a tannin bleed-through problem if covered with a light-colored paint or stain. Unless, that is, you first spot-prime the knots with Zinsser's B-I-N Primer Sealer. It's the only product I know of that keeps the brown tannin spots from bleeding through.

You mentioned that your house is 20 years old and has painted cedar siding. Is it possible that what's on the siding is solid-tone stain? Around here there are hundreds of houses with rough-sawn cedar siding, and while some appear painted, they are actually covered with solid stain. The benefit of solid stain is that it does not flake off over time, but it just sort of fades away.

Last summer I "painted" a large house with a solid-tone stain. It was a product called Rubbol made by Sikkens, and it is supposed to last about 15 years. We did the trim (all made from rough-sawn cedar 1x lumber) in white and the clapboards in blue. It worked quite well.

The point I'm getting at is: the choice of wood may be less important than the choice of finishes. Whatever you choose (which should match the texture of the siding), you will be best served by priming the back and all sides of every piece of trim. I have read a lot lately about the benefits of "back-priming", which deters moisture from getting into the wood from behind, from the sides, etc. You should also carefully caulk all the way around the window trim, between the end of each siding clapboard and the trim. This does not take that long to do. I use a siliconized acrylic-latex caulk such as Alex Plus. There are other products that are stainable, which is important if there is not a color of caulk that matches your finish.

You also might find some helpful people at a local paint supply store... the kind that caters to professional painters. I've found employees at some of these stores to be very knowledgeable.

Also, make sure that the window installers carefully install flashing around the windows (if you are using windows with a nailing flange) to ensure that stray rain does not get behind the window and damage the framing.


Bruce W. Maki, Editor.

Update 2005:

One word: Azek

Azek is an awesome wood substitute for exterior trim. While expensive, more than double the price of wood, it's worth every penny. Azek is cellular PVC, and it's water proof. Period.

Azek can be cut, nailed, drilled, and routed like wood. It can be painted but doesn't require painting. For exterior trim work I won't use wood anymore. I prefer Azek.



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Compiled April 13, 2001