Soffit, the horizontal panel under your eaves, and fascia, the horizontal trim board at the bottom edge of the roof are part of your roofing system. Keeping fascia and soffit in good repair is your best defence against attic pests, such as birds and squirrels. Minor damage, such as loose soffit panels and fascia boards, can be easily repaired. Because of their position at the edge of the roof, boards and panels with serious damage should be replaced.
Inspect the eaves for loose and missing fascia boards and soffit panels. Use an awl to probe wood near loose joints. Plan to replace pieces where the awl penetrated easily more than 1/8 inch deep, which is a sign of dry rot.
Scrape old caulking and paint from loose joints, using a paint scraper. Use a hammer to tap fascia boards or soffit panels back into position. Use 2-inch finish nails to reset fascia boards, two nails in each rafter tail of the loose section. Reattach loose panels using an air stapler and 1 1/2 inch-wide crown staples.
Caulk the seams, nail and staple heads and the edges of reattached loose pieces, using painter's caulk. Smooth the caulk with a dampened finger along the edges and in the joints between pieces for a good finish.
Cut replacement fascia boards from the same size dimensional lumber as the original pieces using a mitre saw (typically 1-by-4 or 1-by-6). Cut the pieces to the same width and length as the pieces you are replacing. Use a tape measure to determine the exact dimensions of the old pieces. Use a table saw to cut luan plywood pieces to replace damaged soffit.
Apply a coat of oil-bonding primer with a disposable brush to all replacement parts, on both faces and all edges. Work in long, straight strokes working with the grain of the wood. Allow the primer to dry for at least two hours before installing.
Pry parts that need replacement from the eaves with a pry bar. Start from the end of fascia boards, working along their length. Pry soffit panels down, working along the edges of the panel. Scrape old paint and caulk from the installation area, and pull any old fasteners with locking pliers.
Fit the new parts in place, in the same position as the original. Nail fascia boards in place with two 2-inch finish nails in the end of each rafter. Staple soffit panels with 1 1/2-inch staples, one staple every 6 inches, into the bottom of each rafter.
Seal the ends and edges of all pieces with painter's caulk.