I am putting fiber cement claps on a small building. I've seen two ways to do the corner boards. Either put the corners on the building first, then butt the siding -or- put up the siding with the corner boards on top of the siding.
Do you have a preference? The installation instructions for the hardiboard show it both ways. I was thinking of putting the corner boards on top of the siding would be a lot easier because I wouldn't have to be so precise with the cuts on the claps.
There are a bunch of ways to do it. I like to nail vertical furring strips to the corners, run the siding, then nail the corner boards to the furring so they cover the ends of the clapboard. You should still seal all cut ends of fiber cement product with paint, even if they are hidden.
---------------------------- Advantages: * Easier measuring of siding. Disadvantages: * Ten times as much caulk. * Harder to get the cornerboard straight.
Siding butted to cornerboard
---------------------------- Advantages: * Lots less caulking. Disadvantages: * You have to be careful measuring.
Suggestions
----------- * Put the cornerboards on first. * Be sure to put factory ends together in the field (where two pieces of siding butt up to each other). The joint will be prettier. * Get those butt joints nice and tight. * Leave just a little space for expansion, no more than 1/8", between the siding and the cornerboard. * Don't align the top edges of adjacent pieces. Hold a straightedge under the bottom edge of the siding to align the new piece to the one already on the wall. The width varies just a little, and the bottom is what will be visible. * Caulk all the vertical joints. Don't caulk the bottom edges--water needs a way out. * Rent or buy the scissors to cut the HardiBoard. The dust from sawing it is awful.
We did 8" lap smooth fiber cement on our new garage. On the recommendation of the building matls supplier, we installed 1" thick corner boards (I think they were deck boards) then installed the siding, relatively tight to the corners, but not perfect, then installed more fiber cement siding vertically on the corners, covering up the 1" boards and lapping over the siding about 3/4" and covering up the not-so-perfect cuts. Overall it looks pretty good, and was easy to do.
Depends on the width and thickness of the corner boards you want to use. Generally about an inch to an inch and a half less than the corner board width. Allow for the corner boards overlapping at the actual corner.
I also like to use an expanded polystyrene corner board, such as Azek.
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