What matters when you’re laying out a coffered ceiling is the size of the finished beam, not the size of the crown molding. And you have to use the Outside Dimension of the full finished beam—the O.D.—not the backing or substrate you might be installing first.
I make my coffered ceilings using what I call “hollow backing.” I make three types of hollow backing shapes or forms: one is for beam intersections and is shaped like the intersection of two streets (see TOP form in the photo to the right).
I make another simpler shape for locations where beams terminate into walls. I use the same form for mid-span backing—when I want to support a beam between intersections, or when I’m running a single long beam across a ceiling. I usually install mid-span hollow backing about every 2 ft. (see LEFT form in the photo to the right).
For ceilings with perimeter beams—half-beams or full beams right against the walls—I use L-shaped hollow backing for intersections (see RIGHT form in the photo to the right).
But don’t be confused by the backing. The real O.D. of the beam is the face of the beam itself, not the backing. When you layout a ceiling, you have to consider the finished O.D. of the beam, from the face of the beam to the face of the beam, then (as Jed Dixon always says), you have to work back to the rough or the backing.
Construction Master Pro
If you’re using a Construction Master Pro calculator, you have to do a little imaginary math. Here’s why: There’s an unequal amount of spaces and beams. In order to make the math easy, you want to work with an even number of beams and spaces—and there’s always one more space than there are beams; unless, of course, you’re installing half-beams around the perimeter of the room (more on that later).
To make the math easier, add an imaginary beam. You can’t add an imaginary space, because you won’t know the dimensions of the spaces until after you’ve calculated the layout. But you do know the exact O.D. of the beams. This technique is very similar to laying out wainscoting: with wainscoting you subtract the last stile; but with coffered ceilings, you add an imaginary last beam.
Let’s use a simple and small ceiling as an example, something we can fit into a tight drawing—an 8 ft. x 10 ft. room. We’ll install three beams across the 8-ft. span. The O.D. of the beams is 5 in. To make the math easier, I’ll add an imaginary beam outside the ceiling, making the calculated span 101 in.
Now the job is easy. Simply divide the calculated span by the number of beams or spaces: 101 / 4 = 25 1/4 in. Remember, that’s NOT the space between the beams! That’s the size of the space PLUS the O.D. of the beam.
To layout the beam locations on the ceiling, measure across the ceiling from one wall, and strike a line at 25 1/4 in. That mark represents the back face of beam #1.
Now use the calculator’s memory to locate the succeeding beams. Press the + (“plus”) button followed by the = button. That sum—50 1/2 in.—is the back face of beam #2.
Don’t press the + button again. Just press the = button to find all other beams. In this case, there’s just one more beam—at 75 3/4 in.; but if there were five more, you’d press the = button to locate the back face of each one.
The CM Pro smartphone application also has a “Tape” feature, so if you forget one of the layout numbers, or when it’s time to pull a tape from the other end of the wall, just hit Convert and then the = button. The CM Pro “Tape” records every keystroke you make, so scroll down through the first few calculations until you get to the series of “Sub-Total=” lines.
Once all the beams have been laid out to their finished dimensions, work back to the rough substrate or backing. I normally snap lines just for the backing, not for the finished O.D. of each beam.
BuildCalc has an advanced “Baluster Layout” feature, and it makes laying out everything extremely fast and easy—from balusters, to wainscoting, to coffered ceilings. If you’re using BuildCalc, check out all the advanced features, especially for laying out stairs.
To use BuildCalc’s “Baluster” feature for coffered ceilings, start by pressing the CONV button, then press the Baluster button (when you press CONV, the “Stair” button changes to the “Balstr” button).
The advanced features in BuildCalc are a little like setting up a story pole—the calculator will do all the mental work for you. Here’s how to set up the “Baluster Function” for a coffered ceiling:
One of these days, BuildCalc will probably be able to calculate coffered ceiling layouts for half-beam perimeters, but right now it can’t, so if you’re not installing full-size beams around the perimeter of the room (that rarely looks good, especially in BOTH directions!!), leave the “Members at ends?” option blank.
Most carpenters like to measure from a wall to the face of a beam, rather than to the back face of a beam. If that’s your way, then be sure to choose Layout Marks at: leading edge—that way you can strike measurement marks at the finished face of each beam, then work forward 3/4 in. and snap lines at the rough substrate or backing. I like to snap lines on both sides of the hollow backing—that way, I never make the dumb mistake of installing the backing on the wrong side of the line.
The last step is to enter the number of beams—and don’t add an imaginary one! In this case, under “Number of Members”, enter 3.
Scroll down the screen and you’ll find the layout measurements: Member 1 is at 20 1/4 in.; Member 2 is at 45 1/2 in.; and Member 3 is at 70 3/4 in.
Oh, wait! I forgot to explain how to lay out ceilings with perimeter half-beams! When I do rooms like that, I just measure in from the wall and mark the finished O.D. of the perimeter beams. I subtract that sum from the overall span of the ceiling, and then use the result as the actual coffered ceiling span—as if the room is made smaller by the perimeter half-beams. Yeah…I bet there’s a much easier way…