Rotted Porch Posts: The Hidden Failure at the Base

Rotted porch posts are the failure owners rarely see coming, because the damage sits at the bottom, behind paint, near the ground, under the porch. The post looks straight and solid from above. A screwdriver tells a different story. A porch post is what carries the porch down to the footing, so a post rotting at the base is a structural problem, not a paint problem.

Why does the base of a porch post rot first?

Wood rots when it stays wet. The USDA Forest Products Laboratory says serious decay needs the wood's moisture content to stay above about 30 percent, and that rain, condensation or wet ground contact will do it, while humid air alone will not (USDA Forest Products Laboratory). Decay is also slow in cold weather and essentially stops at about 35 F. Chicago winters slow it, but every spring thaw and summer rain starts it again.

The base of a post is the wettest place on the porch. Rain runs down the post and pools where it meets the footing or the concrete. Snow piles against it and melts. Water wicks into the end grain. That is why a post can look fine at eye level and be soft within a few inches of the ground.

Wood treated for ground contact lasts longer, but only if it is the right kind. The American Wood Protection Association's Use Category 4A is the rating for "ground contact, general use," and it lists sawn deck and guardrail posts under that category (AWPA). The American Wood Council's deck guide also requires lumber in ground contact to be approved preservative-treated wood suitable for ground contact, and field cuts to be treated with preservative (AWC DCA 6). A post that was cut shorter on site and left untreated at the cut, or standard-grade lumber used where ground-contact lumber belonged, is one way for the base to fail early. Hardware matters too. The guide calls for galvanized or stainless fasteners and connectors with treated wood (AWC DCA 6).

What are the warning signs?

You can check most of these yourself from the yard, with the porch unloaded:

• Paint that is bubbling, peeling or cracking near the bottom of a post.
• A dark, damp or stained base, or a green or black film on the wood.
• A flat screwdriver that sinks into the wood at the base with light hand pressure.
• A post that leans, twists or has a gap at the bottom.
• Wood at the base that is crumbly, stringy or hollow when tapped.
• A porch floor that sags, bounces or has dropped near one post. See why porch floors sag.
• Cracked or loose connections where the post meets the beam or the floor framing.

Do not push on a post that looks bad while standing on the porch above it. Probe it from the ground, and keep people off the porch if it feels loose.

What does Chicago require for porch posts?

The City's rule for existing porches is that they must be maintained structurally sound, in good repair, properly anchored, and capable of supporting the loads placed on them (City of Chicago). Inspectors check joists, beams, columns, stairs, rails, ledger boards, connections and footings (City of Chicago). A rotted post is a column that is no longer sound.

The 2011 City porch guidelines say footings must bottom out at least 42 inches below grade (City of Chicago, 2011 guidelines). Treat that as 2011-era guidance, and check the current requirement with the Department of Buildings.

How are rotted porch posts fixed?

It depends on how far the rot goes, and that is a job for someone who can open it up. The common paths:

• Post replaced, base kept. If the footing and the framing above are sound, the post is replaced with proper ground-contact or code-approved material and fastened with the right hardware.
• Post and footing. If the rot started because the base sat in water or the footing is failing, the footing may need work too.
• Larger rebuild. If several posts, the floor framing or the connection to the wall have gone, the job is a rebuild. Whether a single post can be repaired or has to be replaced is covered in can a rotted porch post be repaired.

On the permit side, Chicago says a permit is always required to repair or replace structural elements such as columns, beams, foundations, stringers and floor joists, with plans by an Illinois-licensed architect or structural engineer (City of Chicago). The same page lists a small-porch exception for a residential porch less than 6 feet off the ground with no more than 50 square feet of landing, so confirm with the Department of Buildings which applies to you. The Express Permit allows repair of existing structures, including replacing up to 50 percent of an existing single-story porch of conventional materials, and anything bigger or different goes plan-based (City of Chicago). Plan-based permits need an Illinois architect or engineer (City of Chicago).

What should you do today?

1. Probe each post base with a screwdriver from the ground. Note which ones are soft.
2. Photograph the posts with a date, including the base and the connection at the top.
3. Keep heavy use off the porch if any post is soft, leaning or loose.
4. Do not wrap the post in trim or pour more concrete around it. That traps moisture.
5. Call a contractor who does structural porch work and ask who draws the plans.

For the other signs that a porch is in trouble, see porch collapse warning signs. If the porch is also separating from the wall, read when a porch pulls away from the building. Our porch team can open up the base and tell you what is there, and our Chicago porch guide covers repair and rebuild decisions.

Common questions

This article explains general rules and common situations in Chicago. It is not legal advice, and City rules change. For a specific property, check with the Chicago Department of Buildings or a licensed professional.