The Structural Fascia Board
“It is our professional opinion that it is poor construction practice to support roof joists on the fascia board at the ends of the roof rafters.” We have rendered this professional opinion with minor variations more than few times.
The fascia board is the one inch thick board that is nailed to the lower ends of the rafters, roof joists, or trusses to close the eave (Figure FB-1). Technically it is not considered a structural member, but it provides structural support for the gutters, when they are nailed to it.
An ice filled gutter can apply about 20 pounds of weight per lineal foot to the fascia board. This weight is usually manageable for the fascia board. However, a twelve foot wide roof for a patio or other addition can apply about 180 pounds per lineal foot to the fascia board. You can see the problem: 180 pounds per lineal foot can easily bend, pullout, or otherwise fail the nailed connection at each rafter unless the fascia board is unusually well fastened.
Figure FB-2 shows a close-up view of a fascia board separated from the ends of the rafters. Note the severe bend in the nails. The moderate corrosion and discoloration on the nail shanks indicate that the nails have been exposed to excessive moisture for years. However, the relatively clean underside of the roof covering indicates that fascia board separated relatively recently.
The support for the roof joists or rafters should be taken back to a ledger board mounted to the studs in the wall of the house. Simpson connectors are helpful in developing enough connection strength for the ledger and the joists or rafters.