What Drives the Cost of a Back Porch Rebuild

Back porch replacement cost in Chicago depends on a short list of things, and none of them is "how big does it look from the alley." We do not publish dollar ranges here, because the same porch can be priced very differently depending on what is under it and what the City requires. What we can do is show you every factor that moves the price, so a bid makes sense when you read it.

What decides the cost of rebuilding a back porch?

Seven things do most of the work.

1. The permit path. This is the first fork. Repairs to an existing porch can sometimes go through the Express Permit. A rebuild that changes size, layout or location needs a plan-based permit with drawings (City of Chicago).
2. Drawings and engineering. DOB says structural repair or replacement always needs a permit, with plans by an Illinois-licensed architect or structural engineer (DOB Porch and Deck Safety). That is a line item before a nail is driven. See do you need drawings to rebuild a porch.
3. How far the rot goes. A porch with soft post bases is one price. One with rot into the joists, ledger and stairs is another.
4. Footings and foundation. What the porch stands on has to be sound. Replacing failed footings is its own scope of work.
5. How many levels, and how big. A rear stack of two or three decks has more posts, more beams and more stairs than a single landing.
6. Materials. Lumber rated for the exposure, hardware, and framing system.
7. Access and site conditions. Alley access, tight gangways, a dumpster, and what is stored on the old porch.

Why does the permit path change the price?

Because the two paths are different projects. The Express Permit allows repair of existing structures, including replacing up to 50 percent of an existing single-story porch of conventional materials, and in-kind replacement. It does not allow new structures, structures that are larger, smaller or in a different location or configuration, legalizing or rebuilding something built without a permit, replacing noncombustible material with combustible (steel with wood), or enclosed porches. Those need a plan-based permit (City of Chicago).

With drawings by an architect or structural engineer, Express can also allow replacing wood with steel, replacing railings to meet current guard height and opening size, and reinforcing members to meet current structural minimums (City of Chicago).

Put it together. A porch that is a repair costs one thing. A porch that is a rebuild, a different size or an unpermitted structure that needs to be legalized costs another, because drawings, plan review and often more of the structure are involved (DOB). Confirm which path you are on with DOB or your designer.

How does the existing condition change the bid?

This is the part you cannot price from the alley. A contractor who quotes a firm number without looking at the framing is quoting the part they can see.

The code's standard is that exterior stairs, decks, porches and balconies must be structurally sound and properly anchored (City of Chicago). Everything that fails that test needs replacing, and the failures that matter are the ones you cannot see: the post bases, the ledger connection, the stair stringers, the footings. For what those look like, see why porches fail inspection.

Rot also moves. Lumber that stays wet decays, so a damaged post often means a damaged beam above it and a damaged stringer next to it. A good bid says what was seen, what was assumed and what happens to the price if the assumption is wrong.

What are the less obvious costs?

Doing it right the first time costs more up front. Lumber for ground contact needs a higher treatment category than lumber used above ground (AWPA), and fasteners and connectors for treated wood need to be galvanized or stainless (AWC DCA 6). Ledgers need flashing and proper lag screws or bolts (AWC DCA 6). A low bid that skips these is cheap for the first few winters.

The public way. Scaffolding, a dumpster or materials in an alley, street or sidewalk need a separate permit from the Chicago Department of Transportation (City of Chicago). Ask who gets it.

The permit clock. An Express permit expires if the first inspection is not passed within 540 days of when work may begin, and DOB says it does not have legal authority to reinstate an expired permit (City of Chicago). Check current rules with DOB.

Licensing. A City of Chicago general contractor license is required for most building construction, alteration and repair work (City of Chicago). An unlicensed bidder is not cheaper if the work cannot be permitted.

What does a cheap bid leave out?

Look for these gaps in any bid:

• No mention of the permit, or "owner pulls permit" with no explanation.
• No drawings, or no engineer, on a structural job.
• No allowance for hidden rot, and no price for what happens if it is found.
• Undefined hardware: "screws" instead of galvanized or stainless.
• No flashing at the ledger.
• No inspection and no closeout.
• Nothing about the alley, the dumpster or the public way.

For the Lincoln Park collapse, City findings cited a porch that extended too far from the building, inadequate supports, undersized flooring and screws that were too small (CBS Chicago). Those are the same places a low bid saves money. Load is another: DOB states 100 psf for porches and decks, but its 2019 slides show 60 psf for a porch serving a single dwelling and 100 psf where it is an exit for more than one unit (DOB). The engineer sets it, not the bid.

How do you get a number you can trust?

Ask each contractor to walk the porch with you, look at the framing, and put in writing: the permit path, who draws it, what is replaced and what is kept, the hardware, the inspection, and what happens if more rot turns up. Compare scopes, not totals.

Whether a porch is a repair or a rebuild is its own question: repair or replace a Chicago porch. Once you know, how a Chicago porch rebuild works shows the steps. Our porch crew gives free estimates, and the Chicago porch guide covers the whole picture.

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.