What wind speed and snow load apply in Wichita?
MABCD, the Wichita–Sedgwick County building department, publishes its own design table. Sec. 2.4.115 of the Unified Building & Trade Code (compiled January 27, 2025) fills in IRC Table R301.2(1) for Sedgwick County:
| Design item | MABCD value |
|---|---|
| Ground snow load | 15 psf |
| Wind speed | "76w/90-3 sec. gust" |
| Wind exposure | Site-specific (R301.2.1.4) |
| Frost line depth | 24 inches |
| Seismic design category | A |
Residential work is still under the 2018 IRC. Commercial work moved to the 2024 IBC on January 1, 2025 (Res. 205-2024).
The wind entry is one older value written two ways: 76 mph fastest-mile equals a 90 mph 3-second gust. It is not an ultimate speed. Today's code maps state wind as an ultimate 3-second gust, and a Meltplan summary of Kansas design loads lists these for the area:
| Risk category (IBC Table 1604.5) | Ultimate design wind speed (3-second gust) | ASD equivalent (× √0.6) |
|---|---|---|
| I | 105 mph | 81.3 mph |
| II | 115 mph | 89.1 mph |
| III and IV | 120 mph | 93.0 mph |
The two tables agree: 115 mph ultimate is about 89 mph ASD, essentially MABCD's 90 mph gust. We design ordinary residential greenhouses to 115 mph ultimate. On snow, MABCD's minimum is 15 psf; Meltplan lists 20 psf, and we size frames and kits to at least 20 psf as margin. Derby's Ord. 2623 carries the same 15 psf and wind entry.
One caution on Meltplan: its table lists a 30-inch frost depth for Wichita. MABCD's table and Ord. 50-833 say 24 inches. Use MABCD.
Ultimate vs ASD: why the same storm has two numbers
Modern codes state wind speed as an ultimate (strength-level) 3-second gust. Many kit makers, older codes and some engineers still talk in nominal or ASD speeds. The conversion is:
V(ASD) = V(ult) × √0.6
For Wichita: 115 × √0.6 = 115 × 0.7746 = 89.1 mph.
That is not a theoretical number. A 2016 steel-building certification letter filed with the City of Wichita lists "Ultimate wind: (3-Second gust) 115 mph" and "Nominal Wind: (3-Second gust) 89 mph" for the same building.
Why √0.6? Wind pressure rises with the square of speed. The basic velocity pressure, before exposure, height and shape factors, is q = 0.00256 × V²:
| Wind speed | q = 0.00256 × V² |
|---|---|
| 115 mph (ultimate) | 0.00256 × 13,225 = 33.9 psf |
| 89.1 mph (ASD) | 0.00256 × 7,939 = 20.3 psf |
| Ratio | 20.3 ÷ 33.9 = 0.60 |
So the ASD speed is the speed that produces 60% of the ultimate pressure. Same storm, same building, different bookkeeping. The mistake to avoid is comparing a kit's ASD rating to the 115 mph ultimate figure, or the reverse.
What does "76 w/90-3 sec. gust" mean?
MABCD's table and Derby's ordinance both list wind as "76 w/90-3 sec. gust." It is tempting to read 76 mph as an ASD number. It isn't. Older codes measured wind as a fastest-mile speed; current codes use a 3-second gust. IBC Table 1609.3.1, "Equivalent Basic Wind Speeds," pairs a 90 mph 3-second gust with a 76 mph fastest-mile speed (table). So 76 mph fastest-mile = 90 mph 3-second gust: the same older value, stated two ways.
- The 90 mph gust is within 1 mph of the 89.1 mph ASD equivalent of 115 mph ultimate.
- Don't plug 76 into the 3-second-gust formula. 0.00256 × 76² = 14.8 psf, about 27% less than 20.3 psf at 89 mph. Treating 76 as a gust speed would undersize the anchoring.
See our Derby page for other local rules.
Exposure: why an open Kansas lot sees more wind
Speed is only half the load. The other half is exposure, which describes the terrain upwind. The DASMA technical sheet quotes the ASCE 7 definitions:
| Exposure | Definition | Where it shows up around Wichita |
|---|---|---|
| B | Urban and suburban areas, wooded areas, or other terrain with numerous closely spaced obstructions the size of single-family homes or larger | Established neighborhoods inside the city |
| C | Open terrain with scattered obstructions generally less than 30 ft tall | Acreages, farm ground and edge-of-town lots in Sedgwick, Butler, Harvey and Sumner counties |
| D | Flat, unobstructed areas exposed to wind over large bodies of water | Rare here |
Exposure C produces higher design pressure than B at the same wind speed. The steel building certified for that Wichita permit in 2016 was designed as Exposure C. DASMA notes many buildings qualify for Exposure B, but that should be shown by evaluating the site, not assumed. A greenhouse on a rural acreage west of Goddard or north of Maize should be designed as Exposure C unless a site review says otherwise.
The anchoring rule
Wind design means nothing if the greenhouse isn't held down. Ord. 50-833 and Res. 080-2017 require every detached accessory structure over 25 sq ft and up to 400 sq ft to be tied down using the City of Wichita's "Non Vehicular Storage Structure Anchoring Standards," or attached to a permanent concrete foundation per R403.1.6.
Derby prints its schedule in the ordinance. Two rows show the logic:
| Building | Anchors | Capacity each | Total hold-down |
|---|---|---|---|
| 12 × 24 ft (288 sq ft) | 4, within 12 in. of corners | 800 lb | 3,200 lb |
| 10 × 16 ft (160 sq ft) | 2, equally spaced | 600 lb | 1,200 lb |
Derby also calls for cable rated at least 800 lb, two clamps per anchor, and a 5/8-inch earth anchor at least 2 ft long or equivalent.
For a rough sense of why that matters: a 10 × 16 ft greenhouse with an 8 ft side wall has 128 sq ft of wall facing the wind. At the 20.3 psf basic ASD pressure, that is 128 × 20.3 = 2,600 lb of push before exposure, gust and shape factors. That is an order-of-magnitude check, not a design, but it shows why a polycarbonate kit sitting on pavers is not enough. The permit guide covers when anchoring is required, and our foundations page covers what to anchor into.
Kit ratings: what to look for
Kit makers often print a wind rating in mph and a snow rating in psf. Before you buy, ask four questions:
- Is the mph rating ultimate or ASD? If it is ASD, look for at least 89 mph. If it is ultimate, look for at least 115 mph. If the seller can't say, treat the number as unverified.
- What exposure was assumed? A rating based on Exposure B may not hold on an open acreage.
- Does the rating assume a specific anchor? Many ratings only apply when the base is fastened to concrete or a specified ground anchor. Pavers and landscape timbers alone usually don't qualify.
- Is the snow rating at least 20 psf? Snow load on a 10 × 12 ft roof at 20 psf is 120 × 20 = 2,400 lb. Lean-to models against a house wall can collect drifted snow, so ask about that case too.
Doors and roof vents are the weak points. A door left open in a storm turns a closed building into an open one and raises the uplift on the roof. Good latches and vent stops are part of the wind design.
Hail is a separate load
Wind and snow ratings say nothing about hail. Wichita has logged 333 hail reports within 10 miles since 2004. On September 15, 2010, a supercell crossed Maize, Goddard and west Wichita. The National Weather Service documented a 7.75-inch, 1.1 lb stone from the swath that ran from Goddard to Udall. The same storm system produced measured gusts of 76 mph in Mulvane.
A frame can pass every wind and snow check and still lose its glazing to hail. Impact resistance is a glazing decision, covered in the hail-resistant glazing guide and our polycarbonate vs glass page.
Frequently asked questions
What wind speed should a greenhouse be rated for in Wichita?
115 mph ultimate for a typical Risk Category II structure, which equals about 89 mph ASD. MABCD's local table states the same wind as a 90 mph 3-second gust.
Is a 90 mph kit rating good enough?
It can be, if the 90 mph is an ASD rating and the anchoring and exposure assumptions match your lot. If it is an ultimate rating, it falls short of 115 mph.
What snow load should I design for?
MABCD's minimum ground snow load is 15 psf, and Derby's is the same. We design to at least 20 psf for margin, which also covers drifting against a lean-to.
Does my small greenhouse need to be anchored?
Yes, if it is over 25 sq ft and up to 400 sq ft. It must be tied down per the City of Wichita anchoring standards or attached to a permanent concrete foundation.
Is hail included in the wind rating?
No. Hail is handled through glazing choice and impact ratings, not wind or snow numbers.
Ready to build?
- Greenhouse foundations — anchors, curbs and footings sized for the hold-down your greenhouse needs.
- Custom greenhouse construction — framing and glazing chosen for 115 mph and Kansas hail.
- High tunnel and hoop house installation — poly tunnels anchored for open-field exposure.
- Polycarbonate vs glass glazing — panels and fastening that stay put in wind.
Get a quote
Send us your lot location and the greenhouse you're considering. We'll check the wind exposure, snow load and anchoring before you commit. Get a Quote.