A.Wood finishes expert Bill Feist responds: The color change in the old wood is caused by ultraviolet and visible light. Since the color change is just on the surface, it could be removed by sanding. Of course, sanding all of the existing roof sheathing and paneling to reveal the blond wood underneath would be difficult and tedious, so the best way to achieve a match is to stain the new wood.
That said, it is difficult to stain new pine to exactly match the color of wood that has been slowly changing for 25 years. You should warn the homeowners that an exact match will not be possible. One trick is to thin out some of the stain used on the new wood to also color the old wood — but only slightly.
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