A.Chuck Green, NARI-certified remodeler and owner of Four Corners Construction in Ashland, Mass., responds: Truss framing can lead to major separations at the intersection of ceilings and interior walls. If your crown molding is assembled from at least two components that can slide independently, it should help disguise some truss uplift movement, rather than be part of the problem. The aim is not to resist the movement but to hide any gaps as much as possible. Where truss uplift is a major problem — that is, where a truss-framed ceiling moves seasonally an inch or more — the solution suggested here may need to be scaled up.

I typically install crown molding with a rough base underneath it. This nailing base is triangular in section, with the outer face fitting between the back of the crown molding and the wall. I also usually install at least one additional piece of flat trim stock — which can be square edged, beveled, rounded, or molded at the bottom — against the...

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