Usually yes for a light steel-roof kit anchored the way its manual says, and usually not — without new footings — for a timber pavilion with a real roof. A typical patio is a 4-inch slab poured on grade with no footing below the frost line; it was never asked to carry concentrated post loads, resist the uplift a solid roof develops in a 115-mph design wind, or stay level while the ground under it freezes 36 inches deep. That does not mean the patio has to go. There are three honest paths — cut pier locations through the slab, set piers beside it, or replace it — and which one makes sense depends on the slab you have, the pavilion you want, and your city's footing rules. This is how we assess it.
Engineering review pending: this page explains what the codes and manufacturers say and how we approach a site. It is planning guidance, not a structural opinion on your slab.
What a patio slab is — and isn't
A patio slab is a thin, wide plate of concrete on compacted ground. It spreads the weight of furniture and people across the soil and moves a little with the seasons. A footing is a deep, narrow mass of concrete that reaches below the frost line so the ground that freezes and heaves each winter is above it, not under it. Kansas City–area cities put the frost line at 36 inches: Kansas City, Missouri by ordinance ("the design frost line shall be 36 inches"), Olathe in its code table, Parkville in its 2024 guidelines, Clay County in its residential regulations, Kansas City, Kansas in its adopted code table. The residential code requires footings to extend below that line.
A commercial pavilion manufacturer puts the problem in one sentence: "Concrete has low flexibility. If pavilion posts are installed into a slab foundation, as the posts adjust with expansions and contractions the forces are applied to the concrete foundation" — and recommends that "the better approach is to begin the pavilion design with footings for the posts" (Romtec, pavilion foundations, accessed 2026-09-30). Builders list "installing posts directly into concrete slabs (causes cracking)" and "shallow footings that don't account for frost lines" among the most common pavilion construction mistakes.
Is your slab a candidate for a light kit?
Big-box cedar-and-steel kits and warehouse-club cedar-and-aluminum kits are designed for anchoring to a sound slab. Their manuals ask for a level concrete surface or concrete post pads, and their anchors are concrete screws or lag bolts into plates at each post. The practical checklist:
- Thickness: at least 4 inches, so wedge or screw anchors can develop their hold; thinner slabs can crack under wind load.
- Condition: level, uncracked, not heaving or settling at the edges.
- Pavers over concrete: the pavers come up at the post locations so the anchor reaches the slab.
- Wood deck: only with "ample structural support" underneath — the maker's words, and the first thing we check.
- What the kit is rated for: one big-box maker claims 100-mph wind and 50 lb/sq ft of snow; one Amish vinyl maker claims 140 mph and 45 lb/sq ft; the warehouse-club maker warns the structure is not for anything that traps wind or snow and tells you to clear snow off the roof.
Done wrong, the slab is the casualty: one consumer complaint we read describes a stamped-concrete patio damaged by improper anchoring of a kit.
Why a timber pavilion is different
A cedar pavilion on 8×8 posts with 4×12 beams, a sheathed and shingled roof and a tongue-and-groove ceiling weighs a great deal more than a kit, and its roof catches more wind. Each post delivers a concentrated load to a few square inches of slab; in a storm the same post pulls up. The slab has nothing below frost to anchor to, and when the ground under it heaves the posts move with it while the roof stays rigid. That is the mechanism behind cracked slabs, racked frames and roofs that leak at the ridge after a few winters. The answer is the same one the code gives for any structure: footings below the frost line at each post.
Your three options
| Option | What happens | Planning cost (national ranges; Kansas City labor) | Disruption | When it is the right call |
|---|---|---|---|---|
| 1. Piers through the slab | We saw-cut or core an opening at each post location, dig and pour a 36-inch pier with rebar, set a post base, and patch the slab around it | $1,500–$4,000 for four piers; $350–$900 for each additional pier (our estimate from national pier pricing plus cutting and patching) | Moderate; the patio stays | A sound slab, posts that land where you want them, and a patio you like |
| 2. Piers beside the slab | Piers go just outside the slab edge; the pavilion overhangs or a strip of new concrete extends the patio | Piers $250–$450 each plus any slab extension at $6–$13 per square foot | Low | The pavilion is bigger than the patio, or the slab is too thin or cracked to cut cleanly |
| 3. Replace the slab | Demolish the patio, pour piers first, then pour a new slab around them with an isolation joint at each pier | Demolition $3–$8 per square foot; new slab $6–$13 per square foot; piers as above | High | A cracked, heaving or thin slab, or a patio you were going to replace anyway |
Sources for the national ranges: HomeGuide concrete removal, HomeGuide concrete slab, HomeGuide pavilion cost (pier footings), Angi concrete footing cost, accessed 2026-09-30. Option 3 is the sequence the commercial manufacturer describes: wrap the footings with expansion-joint material and pour the slab around them, so the slab and the piers can move independently.
Which Kansas City cities let a small pavilion use shallower footings?
This is the table nobody publishes, and it changes the answer for a small structure. Relief applies to the permit — what the city will accept on the drawing — not to whether the structure will move; we may still recommend deep piers.
| Jurisdiction | Footing rule for a detached accessory structure | Source |
|---|---|---|
| Kansas City, MO | Design frost line 36 in (building code amendment); no accessory relief found | Ord. 220353 |
| Olathe | Frost line depth "36-INCHES" in the code table | 15.04.100 |
| Parkville | "The bottom of all footings must be a minimum of 36 inches below finished grade" | 2024 residential guidelines |
| Clay County | "the bottom of all footings must be thirty-six (36) inches below the ground surface" | Residential construction regulations |
| Kansas City, KS | Frost line depth 36 inches in the adopted code table | UG IRC ordinance |
| Lenexa | "Detached accessory buildings with an area of 600 square feet or less do not require frost depth footings" | Accessory structure guide |
| Shawnee | Bottom of foundation must be at least 36 in below grade only if the building exceeds 400 sq ft | Accessory building guidelines |
| Johnson County guideline (used by county cities) | 36 in minimum, but "footings for freestanding accessory structures with an area of 600 square feet or less and an eave height of 10 feet or less are permitted to extend below grade 12" and have a minimum width of 12"" — the document cites an older code edition; we confirm with each city | Residential foundation guideline |
| Overland Park, Lee's Summit, Liberty, Leawood | Frost depth not published online; metro standard 36 in; confirm with the office | — |
All accessed 2026-09-30. A 16×20 pavilion (320 square feet) with 8-foot eaves qualifies for Lenexa's waiver and the county guideline's 12-inch relief on paper, and sits under Shawnee's 400-square-foot line. What that means in practice: in those cities the permit reviewer may accept shallow footings for a small pavilion, and the decision to go deeper becomes an engineering and durability judgment rather than a code requirement. We will tell you which we recommend and why.
Post bases and rot
Whatever the footing, the post never sits in soil or on bare concrete. Wood exposed to weather must be naturally durable (cedar, redwood) or pressure-treated; posts in contact with the ground need ground-contact treatment or a metal base that holds them above grade, with corrosion-resistant fasteners. Kit makers build the same idea into their hardware — concealed knife plates or standoff bases in each post. One builder details piers set about 2.5 inches below the patio surface with ¾-inch standoffs so the post end never sits in water. The owner who wrote "the pavilion front posts are rotting and will need to be replaced" on a ten-year-old structure had posts set the other way.
Runoff
A solid roof turns a 16×20 footprint of rain into two concentrated eave lines. On a flat lot with an existing patio that already ponds, that is a drainage problem you did not have before. Plan gutters and downspout discharge, or at least splash zones, as part of the design — Lee's Summit's code says plainly that patio runoff may not be directed onto a neighbor.
What to ask — and what the permit reviewer will ask
- How thick is the slab, and is it reinforced? (A core at one post location answers both.)
- Where exactly do the posts land, and is there a control joint or crack there?
- How deep will the piers go, and does the city grant any relief at this size?
- Is there an isolation joint between pier and slab?
- What post base, and how far above the slab does the post end sit?
- Where does the roof water go?
- Will an engineer's letter be required? (Shawnee for post-frame and trusses; Olathe lists sealed documents; Parkville sealed plans; budget $500–$1,500 when it applies.)
Engineering review pending
A · Pier through an existing slab
B · Lenexa / county-guideline shallow-footing case
where permitted — ≤600 sq ft, eave ≤10 ft; confirm with city.
The 12-in dimensions come from the older county guideline. Lenexa’s separate frost-depth waiver does not specify these dimensions.
Concept cutaway, not to scale or a construction detail. Slab condition, footing size, reinforcement and connection design need site-specific review.
- Panel A: existing 4-in slab, saw-cut opening, 36-in pier with rebar, standoff post base, cedar post; isolation joint; patch.
- Panel B: Lenexa / county-guideline shallow-footing case, 12-in deep × 12-in wide, where permitted — ≤600 sq ft, eave ≤10 ft; confirm with city. The county guideline’s current local acceptance is unresolved.
Frequently asked questions
My kit's manual says it can be anchored to a patio. Is that a footing? No; it is an anchoring surface the maker designed for a light structure. It is fine for that kit on a sound 4-inch slab and not a basis for a timber pavilion.
Does cutting through the patio ruin it? A clean saw-cut or core, a pier poured below, and a patch with an isolation joint is a standard detail. The patch is visible; stone-wrapped columns hide it.
What if the patio is pavers over a slab? The pavers come up at each post, the slab is treated as above, and the pavers go back around the column.
Will I need an engineer's letter? Sometimes, by city and by structure. Shawnee requires a Kansas engineer's seal for post-frame and trusses; Olathe's residential permit lists sealed construction documents; Parkville's guidelines call for sealed plans. Budget $500–$1,500 when it applies.
Last updated: September 30, 2026. Reviewed by: engineering review pending. Your city's rule: Overland Park · Olathe · Lenexa · Shawnee · Lee's Summit · Kansas City, MO. Ready to have us look at the slab? Get a quote — or price the options in the Instant Estimate.