How to Estimate Soffit and Fascia
Soffit and fascia work together to enclose the underside of your roof overhang, protect rafter tails from weather, and provide ventilation for the attic. Estimating these materials starts with the linear footage of your eaves and the depth of the overhang.
Linear Fascia Formula
Fascia covers the vertical edge at the end of the rafters. The linear footage equals the perimeter of the roof eaves (the horizontal edges where the gutter sits):
Fascia LF=Eave Perimeter×(1 +Waste%)
Soffit Area Formula
Soffit closes off the horizontal underside of the overhang. Its area is the eave perimeter multiplied by the soffit width (the distance from the wall to the back of the fascia):
Soffit Area=Eave Perimeter×Soffit Width
Standard Panel Sizes
Vinyl and aluminum soffit panels come in 12 inch wide strips, in lengths of 12 ft (3.7 m) or 16 ft (4.9 m). Fascia covers usually come in 12 ft pieces with a J-channel that hides the cut shingle edge above.Material Comparison
| Material | Cost / LF | Lifespan | Maintenance |
|---|---|---|---|
| Vinyl | $1 - $3 | 20-30 yrs | None |
| Aluminum | $3 - $6 | 30-50 yrs | Repaint as needed |
| Wood (cedar/pine) | $5 - $10 | 15-30 yrs | Paint every 5-7 yrs |
| Fiber Cement | $4 - $7 | 50+ yrs | Paint every 10-15 yrs |
Plan for Ventilation
At least every 4 to 6 ft of soffit run should be a vented panel to provide intake airflow for the attic. Continuous vented soffit panels give the most consistent ventilation. Pair with a ridge vent for balanced exhaust per IRC R806.