Soffit and fascia basics
The soffit closes the underside of the roof overhang, between the wall and the roof edge. The fascia is the vertical board along the roof edge, where the gutters attach. Together they protect the rafter tails from weather and pests, and vented soffit panels supply the intake air for attic ventilation.
How the calculator counts soffit panels
Vinyl and aluminum soffit panels are usually installed perpendicular to the wall, cut to the depth of the overhang:
- Pieces needed = eave length ÷ panel exposure (the width each panel covers), plus waste.
- Pieces per panel = panel length ÷ overhang depth, rounded down.
- Panels = pieces needed ÷ pieces per panel, rounded up.
Example
120 ft of eaves with a 16 in overhang, using 12 ft panels with a 12 in exposure:
- 120 pieces, or 132 with 10% waste;
- each 12 ft panel yields 144 ÷ 16 = 9 pieces;
- 15 panels;
- soffit area: 160 ft²;
- fascia for 120 ft of eaves plus 60 ft of rakes: 198 ft with waste, so 13 boards of 16 ft;
- 22 pieces of 12 ft channel (F-channel at the wall and J-channel at the fascia);
- material cost at $18 a panel and $25 a board: about $595.
Plan the cuts: with a 20 in overhang, a 12 ft panel only yields 7 pieces, and the leftover 4 in is waste.
Vented or solid?
Use vented soffit panels where the attic needs intake air, and solid panels elsewhere, such as over porches or where the overhang does not connect to the attic. A common rule is 1 ft² of net free vent area for every 150 ft² of attic floor, or 1 per 300 ft² with a balanced intake and exhaust system and a vapor retarder, with about half of it at the soffits. Check the net free area printed on the panel packaging.
Fascia materials
- Wood (pine, cedar) is traditional and needs painting.
- PVC or composite boards do not rot and need little maintenance.
- Aluminum fascia wrap covers an existing wood fascia; it is bent on site with a brake.
Replace any rotten fascia before installing gutters, since it carries their weight.
Installation tips
- Check that the overhang is level and the fascia straight; add nailers where the panels need support every 12 to 16 in.
- Leave about ¼ in at the ends of panels and channels for thermal expansion of vinyl, and do not nail tight.
- Keep insulation from blocking the vents: install rafter baffles at the eaves.