After much research, we have found the horizontal glue laminates for the gable detail as engineered to be cost prohibitive and dimensionally incorrect. Since we changed the gable fascia from 12 inches to 8 inches, an 8-inch horizontal arched beam is more appropriate. Hence we have opted to join two each 5/4 x12 x16 smart lap trim boards via glue and screw and then cut to arch. The depth of arch dimension should be 4 inches at C/L depending on best practices and determined by the builder.
The length of the arched beams on the two smaller gables to the left and right of the main gable can be no more than 96 inches, so the position of the lower corbels is predicated on this dimension and the location of the top apex of the arched windows. Again, the location of the lower corbels is predicated on 96 inches and best practices as determined by the builder.
The reason why we are limiting the arched beam length on the smaller gables is that we are using 2 each 5/4 by 12 by 16 trim boards to make two separate arched beams. If however, the length of 96 inches is inadequate then we will purchase two more boards. The initial distance will be determined by placing a horizontal 2 by 4 at the apex of each arched window from gable rake to gable rack.
The large center gable horizontal arched beam length will be determined by the installer.
The lower corbels will be made from one 20 inch piece of smart lap trim board backing board (5/4 x 4×20 inches)
An 11 inch long lower corbel cut from 4 by 12.
And a 15 inch 4 by 4 horizontal protruding
The 20-inch piece of backing board can be temp installed with sheetrock screws to facilitate siding install. The upper aspect of the backing board end will be cut to fit snugly against the freeze board at the appropriate angle. The upper 4 x4 x 15-inch horizontal protruding pieces can be mounted to the freeze board via angled and counterbored screws.
Please look at existing drawings and hand drawings.