Although most people don't take it into consideration, the width of the fascia board should be included in your calculations. The reason being is that is is the top outside edges of these members that will need to match after the fact. In most cases the width is .75" (1 x lumber). However stacked fascias or perhaps in rare instances a 2x4 fascia board may be used on the job. Verify any additonal horizontal factors that may affect the over-hang assembly depending on the soffit finish prior to working your calculations on the job.
NOTE
Remember that if you subtract a negative number, it becomes a positive. So if your match point falls below the Top Plate line (which it usually does), therefore making it a negative number, add it to the plumb before subtracting the drop to achieve your lug dimension.
WARNING
If for any reason a top chord member must be adjusted in size (say from a 2x4 to a 2x6), you may need to rework your match point depending on the circumstances. The plumb of the stick is different for each lumber size (see plumb chart) and slope and must be taken into account when working with these variables. If you change the top chord that controls the match point, be sure to rework your other fascia drops accordingly.
NOTE
Any combination of pitches may be used to run these calculations. If your over-hang = 12", then the drop = the pitch. If your over-hang must be adjusted, the following formula is used to set up the proper ratio drop for you.
Drop/Overhang = Pitch/12
NOTE
Due to the excessive lug cut on the 12/12 pitch example, a wedge must be incorporated. The lug cut is 5-1/4", whereas the bottom chord (assuming a 2x4 is used) is only 3-1/2" deep. All framing members not only must meet but must provide adequate plating surfaces to transfer the loads throughout the trusses. Your truss fabricator will size any required wedges. In this example the "lug" is not cut from the bottom chord at all. Instead, the heel of the truss must be raised to complete the lug definition as used in these examples.
Plumb (+) Lug = OWH (over-the-wall height)
OWH (-) Drop = Match Point
NOTE
The match point is only determined in the first formula. You will set the lug, usually 1/4" (but not always). After that, the lug, as a rule, becomes the unknown factor to determine the OWH.
