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Q.We all know truss uplift can be a problem at the intersection of ceilings and interior walls. Is there a way to install crown molding so that you don’t see a paint-line reveal when the ceiling moves?

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 wall, behind the crown molding. This additional trim improves the look of most simple moldings. When truss uplift is a concern, two pieces of flat trim will be needed.

Start by installing the first piece of flat trim stock to the wall. Then, before installing the triangular nailing base, nail or screw the second piece of flat trim to the back of the triangular nailing base. Next, install the triangular nailing base by nailing it or screwing it to the ceiling. Finally, the crown molding can be installed, using longer finish nails at the top of the crown, and very short brads at the bottom. Since the crown molding is fastened to the ceiling not the wall, some truss uplift movement can be accommodated between the two pieces of flat trim stock.

All of the pieces except the triangular nailing base will need to be prefinished, to allow movement to occur without revealing a line where the finish or paint stops. The crown molding will look best if the second piece of flat trim has a molded bottom, to help disguise the unsecured sliding joint between the two pieces of flat stock.

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