I am having my 50 year old new england colonial home renovated. It was re-sided about 10 years ago with Maibec white cedar factory treated with bleaching oil. I haven't done anything to the shingles since they were applied. I am now having an addition put on the back of the house and the front is being partially re-sided as we are making some changes to a side entrance and garage. I'm thinking that I should use untreated white cedar for the new siding and then power wash the 10 year old shingles then apply a semi transparent stain to both sections to try to get a close match. Any suggestions?

Thanks to everyone for the insights and suggestions. Am now confident that our shingles are not CCA treated and very doubtful that anything else was applied for a variety of reasons. One other relevant observation is that subterranean termites had tunneled through a defect in the slab ledge, up the back of the brick veneer, and into the cedar shingles. There were thousands (tens of thousands?) of the little beasts found eating a large section of cedar when the contractor pulled off the composition roof the previous owner had installed over the original. Just recalled this wouldn't have happened in the presence of CCA, though unsure how much they would have been bothered by other possible preservative/retardant chemical treatments. I probably gave too much emphasis to CCA in the initial post because it was my greatest concern in using as mulch for reasons discussed earlier. The broader question is whether there were any chemical treatments for cedar shingles in common use at the build time and location that would still pose a danger in mulch/compost. I couldn't find any that would not have leached, eroded, or otherwise broken down sufficiently by now. If you have an interest or are bothered with insomnia one night, Performance of Preservative-treated Wood Shingles and Shakes (pdf) gives a good summary of treatment options at around 1995. Also read somewhere that a tablespoon of ash from CCA treated wood is considered a lethal dose for humans. That's a lot to ingest unintentionally, but a reminder of how dangerous this stuff can become if mishandled.

Thank you for your help!! The bumped out portion on the front has the cedar underneath, getting ready to unveil. I’ve been told by someone that in order to keep the home listed as “contributing” in the NRHP that I need to have the addition match (with the same cedar). Just checking to see if that really is the case? Thank you

I must say, the aged look of the shingles is quite beautiful to me. Sounds like (from the above) that doing your spot repairs as needed could be the way to go, both esthetically and financially. May I ask pros for more detail about how you would prep either for clear finish or paint if thats the route someone wanted to go? If wood is dark do you assume that its mildew (prob use deck clearner type product?) or is it just some natural aging (patina) of the wood that could take a clear finish over it? Just curious - dont have a shingle house at the moment but almost did once. If the damage is limited conceivably OP could use an epoxy-base d wood hardener + wood fill product on it? Generally my experience with 100 yr old wood is :-) and not :-( This is likely still old growth timber and as such was hard as nails very unlike the farmed wood of today (and still is, if its not too rotted) Was so shocked when I got some cedar trim milled for my old porch at how soft and splintery it was - nothing like the existing wood. And I would reiterate about trying to find someone local who is old house friendly and has wood restoration in his/her repertoire - either to do the actual work or you pay them for a consultation. Your plastic guys - siding, windows, etc. - have their own business model and ways of doing things so you really cant expect them to be knowledgeable in other methods. Its fine with me if thats what they want to do, but where I have a problem is when they dont recognize their limitations and make these pronouncements about how the old siding or windows have to go .... like its some kind of ulitimate truth. Consequently, a lot of people dont look any further and the end result is ... at least in my neck of the woods.... a lot of plastic-clad houses.