Why the house side goes first
The National Park Service's guide to wood porches says porch floors should slope down toward the outer edge, at least 1/4 inch per foot, with boards running in the direction of the slope. When that slope is lost, water ponds instead of draining, and the Park Service names ponding and cupped floorboards as signs of it. On a porch that has settled toward the house, the low spot is right against the wall.
Three other water paths end at the same spot:
- The door sill. The Building America Solution Center's door and window flashing guide calls doors a weak spot for leaks and says they need pan flashing under the sill to send water out instead of into the wall.
- The ledger, which is the board that fastens the porch frame to the house. BASC's flashing checklist lists ledger flashing, head flashing over doors, and gutters and downspouts as details to look for, and says to hire a contractor if any are missing.
- Roof water. The Park Service warns against letting the main roof's gutters and downspouts drain onto a porch roof, and notes that flowerbeds and mulch sloped toward the house hold moisture against the porch.
Soft boards or rotten framing?
The Park Service says floorboards can also fail because the framing underneath is moving. A soft board over sound joists is a small repair. A soft area over a rotten joist or a loose ledger is a structural one. BASC's porch and deck attachment guide says many porch and deck failures happen without warning, mostly at weak connections between the ledger and the house, and that rot and corroded fasteners often contribute.
Clues you can check from solid footing:
- Is the softness one or two boards, or a strip running the whole length of the wall? A long strip points toward the ledger or the wall junction.
- Does the floor dip toward the house, or does water sit there after rain?
- Is there a gap opening between the porch and the house, or is the floor springy beyond the soft spot?
- Can you see the underside? Look for dark, crumbling or wet framing and rusty hangers or bolts. The Park Service also notes that boarding up the lattice skirting traps moisture underneath.
The Park Service's method for finding the extent of rot in a board is to probe gently with an awl. Do that only while standing on sound flooring. Don't bounce on the floor to test it, and don't crawl under framing you're unsure about. If boards are breaking or the porch is pulling away from the house, keep people off it until it's looked at.
Who to call and what to ask
Start with a carpenter or contractor who repairs porches and will look underneath, not just at the boards. Bring in a structural engineer if the ledger connection, joists or roof posts are in question. If the water is coming from a leaky door sill or flashing, the fix may need the door installer or a roofer as well. Our guide to deck joist and post inspections covers what the framing check should include, and our flashing guide explains where roof-to-wall leaks start.
The North American Deck and Railing Association's deck evaluation guide is a checklist covering footings, posts, beams and joists, the ledger, and the deck boards. It's a useful outline to compare against a contractor's inspection. Ask for:
- Photos that show which damage is in the boards and which is in the framing.
- Where the water is coming from, and how the repair stops it, not just new boards.
- Confirmation that the new floor will slope away from the house.
- On an older porch, replacement boards that match the old ones in thickness, width and profile, which the Park Service recommends.
Permits in Philadelphia and the suburbs
Philadelphia's building permit page says major repairs that go beyond regular maintenance need a building permit, and that the usual exemptions assume the property is not on the Philadelphia Historic Registry. Its EZ permit page lists residential decks up to 216 square feet among projects that can get a permit without plans. Replacing framing or the ledger is not the same as routine maintenance, so ask your contractor who will pull the permit. In Bucks and Montgomery counties, the township or borough code office decides. Our deck repair permit guide compares the two.