Hello. I’m a new participant here. I’m looking at plans that feature a 14′ circular room with a dome ceiling. The center of the dome is to be 16 ” higher than the perimeter. I can work out several framing schemes, but I don’t know how the ceiling could be skinned, aside from plaster and wire lath. Is there a simpler, less “expert” way? Any tips out there for framing or surfacing would be most welcome. And if plastering is the only realistic approach, what sort of trowel would be best?
Thanks!
Replies
Try http://www.radiustrack.com
Might put you on the trail of finishing methods.
Or . . .
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=92083&item=7522162442&rd=1&ssPageName=WDVW
Do a search here for the thread Satelite (Satlite) dish. A discarded dish was used to form the dome and some ingenious jigs were made to aid in the finishing.Remodeling Contractor just outside the Glass City.
Quittin' Time
A trade magazine called 'Jobsite' recently landed in my mail. It's gone now but there was an ad for a steel-channel dome ceiling framing system. Specify your horizontal and vertical radii and they fab it up and ship it to you in pieces RTA. I would track that down and call the rep. Doubtless they know of ways to handle the facing. A commercial steel framing supply house may have good info for you.
I'm sure the easiest one is going to be plaster over expanded metal lath. If you bid the job you will need an extremely good plasterer.
In a current commercial job I'm trimming out, all of the halls are barrel vaults with the intersections either domes or groin vaults. The domes and vaults were a composite gypsum and fiberglass and came in pieces that were assembled by the framers and then taped and mudded by the finishers. We then applied panels and ribbing. I'd have to chase down the GC to find out who made the arched and domed panels but your local drywall supplier may know of one local to you.
On the floor describe the circle that will be the circumference of your dome at ceiling level,. Then snap a line down the center. and layout from the center each way on (I would use) 8'' center. This shows your dome in plan view.
You said the rise of the arc in the center will be 16''. Make sure you leave enough room so that you can install your arced frames in one piece, meaning drop a couple of inches if this distance takes you right up under the existing ceiling joists.
Now you want to create a section view of your dome at the center line. There are different ways to do this but the way I was taught, (I think I learned it in the pages of Fine Homebuilding) is to snap a line on the floor, tic off the total run, length of chord. Then create a perpendicular bisector, a square line from the center of the line segment. Measure up the bisector the same number of inches that you want for your total rise 16''. Now connect this point to either point on the original line and make a perpencular bisector to this new line segment. The point where these two perpendicular bisectors intersect is the center of the circle. Describing this arc will give you a section of the center of the dome. Now layout, on 12'' or 16''centers, this arc exactly the same as the other. Make sure your layout is equidistant from center on both sides. This will allow your to make two of each off the arc frames, one for each side and make less work.
Using the dome in plan view you can measure each of the runs. They get smaller as they get farther from center. Using the section view laid out will give you the rises in the same way. Having the rise and runs and the method I described above for finding a circles center you can use these measurements to describe new section views. The section views can be transferred to ply wood cut out and installed as rafters. Any perpendicular blocking can be described in the same way. I hope this isn't to confusing, if you scale down and lay it out witha compass on paper you will learn the technique, and see that it is not really as complicated as it seems. But I'll be glad to answer further questions. As far as the skin your dome has a lot of run in proportion to its rise, I would try some 1/4'' sheetrock. And experiment, But maybe a pro will come by and give us some good advice. This is by no means the only way. But I sure am tired of hearing about that sattelite dish.
USG makes the Grid-x system (like t-bar for drywall) and we have used it to frame similar domes, they have instructions on how to get started.
You can have the dome made up in 1,2 or 4 sections out of a gyp,glass composite. These are pricey and require waiting periods. They are also fairly hard to install, support and require access from above during installation.
Framing a dome isn't that tuff, just draw the curve from side to center and make up the pieces connecting at center.
Lath and plaster is the best, but I have seen domes similar to yours sheetrocked with 2 layers of 1/4". I said "no way will it work", but was proved wrong. Just don't let any yahoos atempt it.
Could you make a pattern for the dome's section as described by Quicksilver, halve it and copy it radially around the center? Since a dome is an arch spun around it's center, these arch beams would then create the shape and allow you to cut and use identical pieces. I would imagine that blocking would be needed between to firm up the structure, perhaps cut one full arch and set inplace to work around.
Here is a page that shows how to get a radius when all you have is the arc and a chord:http://mathforum.org/library/drmath/view/55037.html This is great when you have to create an arch when all you have is the height at the peak, the width of the chord (jamb distance) and the rise (difference between total height and at what point the arch "breaks" from plumb.
As far as finishing, do you have to wet the back of the quarter inch rock and set in the sun ontop of a bucket to let it sag? Best leave that to a pro finisher to answer.
That approach wiil work fine. And certainly is the more obvious. I wanted to suggest the approach I described because you can use it to describe an elipitical "dome' also. I really think arches and elipses are fun, and hope that carpenters will embrace traditional methods. Thanks for the link.
On shallow ellipses, the method of using two foci and a loop of string does not work. The stretch of the string will lead to inaccurate results. Even dacron, steel, graphite, and others have too much stretch.
Recently, I faced the task of creating an elliptical dome in an elliptical shaped coffer. The opening for the coffer was 9.5 feet on the short axis and 19 feet on the long axis. The elliptical dome inside this coffer was only 11 inches high. We couldn't get any kind of line to work with traditional methods. Here is what we did.
First I drew the ellipse in autocad. I wanted 64 ribs for the shape so I used autocad to segment the elliptical line into 128 segments. I deleted every other one including the minor and major axis. This gave me four identical sets of 16 ribs. I simply needed 16 patterns. I used autocad to derive the length of each of these sixteen segments from the segment point on the edge to the center point.
Once I had the lengths of the ribs, I used autocad to create an ellipse with a minor axis of 11" and a major axis of each of the the rib lengths. After I had created the 16 ellipses, I quartered them. I now had the shape of my 16 ribs. I added a horizontal and vertical axis line. On the horizontal axis line, I added six inches in width to each shape so that it would not come to a long sharp point. More on that later. I then nested them together inside a rectangle that was six feet wide and 48 feet long.
This is where the fun part starts. I took the electronic file to a shop that makes sails for sailboats. They had a computer controlled cutting table. They rolled out a sheet of reinforced mylar on the table and fed in the electronic file that I supplied them. The machine then cut out our sixteen patterns. I took these back to the job.
We used 1 1/8" plywood for the ribs. We layed the patterns out, subtracting back out the six inches that we added for strength. Then we just spray painted a stencil of the pattern onto the plywood. We made four of each pattern and then fastened them into place.
For the center, I determined that I could use an ellipse of a certain size that I figured out mathmatically. I cut this out of 3/4 plywood and the size of it allowed me to zip off each rib to butt into it. The cut ends were 1" thick and the shape just flowed into the 1/4" difference in thicknessbetween that and the 3/4" plywood center. The finish will be done in plaster of course. The 3/4" center ellipse section was about 34" long and 17" wide and I had the computer cutting machine cut it out and lay out the segments in pen from a layout that I included in the electronic file. The machine can use either a cutter or a pen.
The autocad work took me 45 minutes. The cutting machine took another 45 minutes. Making and installing the ribs to two men two days. The frame was too pretty to cover. I thoroughly enjoyed developing the method and executing it and when we were done we just through the patterns in the dumpster. I really doubt that I will be asked to do this again and if I did the dimensions would be different.
Traditional methods are fine but developing new methods that work better are at least as fulfilling.
I think I will cross post this to a new thread and hope no one will mind.
Excellent post--you are one bad dude! I just want to know why there's a canvas shop in Austin.
Lake Travis, Lake Austin, Lake LBJ, Lake Marble Falls, Lake Buchanan, and Inks Lake are all in the area. They also make awnings but the owner is one of the best sailors in the area. In the sailboat races that they hold every weekend, if he is on your boat, you stand a good chance of winning.
Ray I saw you started a new thread so I posted this again This is the kind of discussion I really like.
Sounds pretty cool. Although I dont' know how to use autocad. . . yet. I never said anything about using a string and nails to describe the elipse. a simple method of describing an elipse was taught to me some years ago. This approach will give you a quarter elipse, simply reflect it to get a half and reflect again for a whole and you will be able to describe an elipse of any size. I think any good carpenter should be able to produce this in the field. I post this in hopes that someone picks it up. Any elipse has a travel distance - run, and a rise. Snap a line on the floor and make a line square to it. Now measure and mark the run on one and the rise one the other. Now divide the run into X number of equal parts one to two inches per part. Now divide the rise into the same number of equal parts.. When your done you should have the run line ticked off lets just say 24 ticks one inch apart for a 24 inch run, and the rise of say 10 inches ticked 24 times also, comes out to .416, rounded down, or 7/16 light. I figured that on a calculator but in the feild I use dividers. OK the connect the line closest to the axis on the run to the one farthest away on the rise, the the second closet on the run to the second farthest away on the rise., and so on. You will see the quater elipse appear and described. so that it can be jigsawed for a pattern. This method again is probably not as accurate as autocad but I can produce this any time I'm on a job in the matter of minutes, same with the method I described above for finding a circles center with only a chord and an amount of rise. You obviously don't need advice, but others amoungst us might. I am just trying to share methods that have allowed me to do some pretty cool work in the past. ThanksEdited 6/16/2005 5:07 pm ET by quicksilver
Edited 6/16/2005 5:36 pm ET by quicksilver
I'm curious as to why you didn't just take the file to a cab. shop w/ CNC machinery & have it made there?
I could have but it would have been more costly to make 64 ribs at cnc machine rates. I talked to my cabinet guy about it. Good idea though.