How to Replace a Clay Tile Roof Underlay

Expose the fasteners that secure the top course of clay tiles to the roof by pulling off the ridge roll tiles at the top of the roof line. Cut the tile mastic that might be spread between each overlapping roll tile with a utility knife or sharp chisel. Pull the overlapped end up to dislodge the nail fastener.

Grab the bottom edge of each top course clay roof tile and swing it up away from the roof to dislodge any fasteners and unhook the top head lug from the wood battens. Repeat the clay tile removal process to expose the full lengths of wood battens and underlay.

Slip the flat end of a pry bar between the bottom of the wood battens and the roof sheathing. Push down on the pry bar's back handle to force the battens away from the roof sheathing. Flip the battens over after you pull them from the roof sheathing, and hit the nail tips with a hammer until they are flush to the wood surface.

Pull the felt underlay up by hand, if possible. Scrape the underlay off of the roof sheathing using a squared roofing shovel, if you can't remove them by hand. Inspect the roof, removing any fasteners or objects that protrude from the plywood sheathing before laying the new felt.

Hook the butt end of the tape measure to the roof eave. Stretch the tape along the roof rake to the width of the felt paper you're using and place a mark. Repeat the process at the opposite side of the roof and stretch out a snap line between the two marks. Snap a straight line across the roof sheathing to represent the first felt paper course.

Set the roll of felt paper on the roof and hammer tack the end flush to the rake edge. Roll the felt paper out across the roof, keeping the top edge flush to the snapped chalk line. Place a roll of staples vertically down the width of the felt paper every 12 inches while unrolling the underlay using the hammer tack.

Measure 3 inches down from the top edge of the felt paper that you laid down on the roof sheathing and place a mark. Follow with a matching mark on the opposite side of the felt paper and snap a line from mark to mark. Roll the next course of felt paper down across the roof with the bottom edge flush to the snapped line. Secure the felt paper in the same manner as the first course using a roll of staples every 12 inches.

Repeat the process of laying the felt down with a 3-inch overlap for each course of felt paper. Overlap any butted ends of felt paper a minimum of 4 inches.

Reinstall the wood battens across the length of roof followed by the clay roofing tiles.