Re: Installing exterior cedar window trim
Normally the trim is installed before the siding and against the sheeting. What I would do in your circumstances is hold the trim on the window, draw a line along the edge, set a circular saw to the depth of the siding and trim the siding back so you can mount the trim. You will caulk where the siding meets the trim on the side and bottom. On the top you should install a drip cap and flashing like this
That way all the water running down the siding will not leak behind the top frame.
Hope that helps
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