What can I do to fix rotting fascia boards?

To fix rotting fascia boards that cap rafter ends and support gutters, you need to assess extent of rot and choose repair or replacement to prevent gutter failure and water damage. For minor surface rot where wood is soft but structure is solid, you can repair by scraping out rotted wood with chisel, applying wood hardener that consolidates soft wood, filling with exterior wood filler or epoxy that is sandable and paintable, sanding smooth, priming with exterior primer, and painting with exterior paint to seal against moisture, costing 20 to 50 dollars DIY. For moderate rot where fascia is soft and crumbling but rafters are solid, you may need to cut out rotted section and splice in new piece of matching wood using scarf joint and exterior wood glue and screws, ensuring joint is sealed. For extensive rot where fascia is severely deteriorated, sagging, or causing gutters to pull away, full replacement is needed: remove gutters, pry off old fascia, inspect rafter ends for rot and repair if needed, install new rot-resistant fascia board such as PVC, cedar, or pressure-treated pine or aluminum-wrapped wood, securing to rafters with nails, priming and painting, and reinstalling gutters with proper slope. Address cause of rot, which is often gutter overflow from clogged gutters, ice dams, or lack of drip edge, by cleaning gutters twice yearly and ensuring proper drainage away from fascia. Professional repair costs 6 to 20 dollars per linear foot.