Curved Molding for Elliptical Windows
Wood as the Primary choice for Curved
If you are lucky the curved molding to match your elliptical window came with the window itself. That way you have a guarantee that it will fit properly. You'll also save on sticker shock, if you don't have to purchase such a curved casing independently.
A standard curved casing for say a 5' diameter elliptical window can run you upwards of $225 - $300. Much of this money is going to the freight company that has to ship a relatively delicate, custom made item from a specialized molding manufacturer.
Thus if you are just at the window buying stage you may want to trouble shoot this ahead of time and insist that the window manufacturer supply not only the window but the curved casing to match.
If you are not so lucky and need to order a curved wood trim to finish off around the perimeter, here are a few details for ordering the correct trim for an elliptical window:
1. Most window manufacturers have a standard shape. From what I have seen it is profiled as below. If you draw a line from left to right across the window where the curvature stops, and then measure straight up to the inside edge of the curved jamb the standard seems to be 17".
Try this and see if it works and then ask your local supplier if you are able to give him the name of the window manufacturer and the width and height,"Is that enough information to guarantee an exact match?" A standard curved trim package is usually cheaper.
2. If not then you only have one alternative. It will be necessary to first fabricate a template. Not all elliptical windows are made with the same height width relationship so a template is really the only way to assure that the right curved trim piece gets made to match your window (especially true if you can't provide the name of the window manufacturer). Therefore here's some info on making the template.
Making a Template for An Elliptical Window:
Tape a piece of paper to your window (you can use a paper table cloth if you don't have a better alternative). Using an exacto blade, cut slashes in the paper with the blade tight up against the inside jamb of the window (see "cut edge for template" in drawing below).
Don't cut more then 3" long before you remove the blade and skip the next 1", and then restart. This is so the inside piece of paper doesn't start falling apart on you before you've have had time to make it all the way around your window. Use a marker to show on the left and the right where the radius stops (ie. where it becomes a straight piece of casing dropping to the floor).
Remove the tape and lower the pattern to the floor. Finish cutting through the paper in all the 1" 'tabs' that you left in place to hold it all together. Cut your pattern straight across the bottom from left to right marks.
Indicate on the template, what you would like to add to this dimension for the "relief" on the jamb (usually 1/4"). Make sure that the supplier understands that you need the casing to be 1/4" larger all the way around!
A typically curved molding for a common sized elliptical window will come in a minimum of two pieces, necessitating a splice, or seam at the top. Larger windows may come as 3 pieces. Ask.
Don't forget to order matching "casing legs" and specify the type of wood AND the profile or pattern you would like your curved trim to be fabricated from.