A greenhouse is the only thing in your yard that has to survive every storm with its glazing intact. 🌪️ Which makes two numbers on the spec sheet more important than almost anything else on it: the wind rating and the snow load rating. This guide explains what they mean, what they do not mean, and how to check yours against where you actually live.
The short version: look for published numbers, match them to your local design values, and understand that both ratings assume the structure was anchored exactly as specified. That last condition is where most failures actually originate. ⚓
💨 Wind ratings: what the mph figure means
A wind rating states the sustained wind speed a structure is designed to withstand without structural failure, assuming correct assembly and correct anchoring. 🏗️
Three things it does not mean:
- ❌ It is not a guarantee. It is a design value, and a gust in a turbulent site can exceed the sustained figure locally.
- ❌ It does not apply to an unanchored structure. A greenhouse held down by its own weight has no rating at all, whatever the box says.
- ❌ It does not survive a modified structure. Removing bracing, leaving a door open in a windstorm, or substituting fasteners invalidates the assumption.
For reference points you can compare against: our aluminum-framed glass models are rated to 115 mph and the polycarbonate range to 65 mph. Those are different because they are different structures for different jobs, not because one is a lesser product. 📊
How to find your own number
Building codes assign design wind speeds by location, and your local building department holds the figure for your address. Broadly: 🗺️
- 🌀 Coastal Florida, the Gulf and the hurricane-prone Atlantic seaboard carry the highest design values in the country, and accessory structures can face specific requirements there.
- 🌾 The Great Plains and tornado alley face high straight-line wind events regardless of the design value.
- 🏔️ Exposed ridgelines and open plains anywhere experience far higher local speeds than sheltered suburban lots a mile away.
- 🏘️ Sheltered inland suburbs typically sit at the low end.
⚠️ The site-specific factor matters as much as the map. A greenhouse in the gap between a house and a garage experiences accelerated wind. One behind a permeable hedge experiences considerably less.
🌨️ Snow load: the number that is usually misunderstood
Snow load is expressed either as a depth or as a weight per unit area, and the weight version is the meaningful one, because snow density varies enormously. ⚖️
- ❄️ Fresh dry powder is very light. A foot of it weighs a fraction of what people assume.
- 💧 Wet, settled snow can weigh several times as much for the same depth.
- 🧊 Ice, or snow that thawed and refroze, is heavier again and the genuinely dangerous case.
So a rating quoted as a depth, such as the 3 ft figure on our polycarbonate range, is a useful shorthand rather than a physical constant. The condition that actually threatens a structure is not the deepest snowfall of the year. It is a moderate fall followed by rain, or a partial thaw that refreezes. 🌧️
What actually carries the load
- 🏗️ The frame and its bracing. This is where snow load lives. Glazing thickness contributes almost nothing.
- 📐 Roof pitch. Steeper roofs shed snow rather than accumulate it, which is the entire design logic behind pointed and gothic-arch profiles.
- 🪟 Panel span. Wider unsupported spans deflect more under load.
💡 A common misreading worth correcting: thicker polycarbonate does not raise the snow rating meaningfully. If you live somewhere with heavy snow, the frame and the roof geometry are what you are shopping for, not the panel spec.
🪨 Hail, the third load nobody rates
There is no standard hail rating on backyard greenhouses, which is unfortunate because in parts of the country it is the most likely damaging event. 🌩️
What we can say factually: polycarbonate is dramatically more impact-resistant than glass, to the point where it is used in machine guarding and riot shields. Tempered glass is several times stronger than annealed and fails safely into blunt granules, but nothing glass does matches a polycarbonate panel for hail.
If you live in the hail corridor running roughly from Texas up through Colorado, Nebraska and the Dakotas, this should weigh heavily in the material decision, and it is one of the few cases where we would say the choice is not simply a matter of preference. 🌽
⚓ Anchoring: where ratings are won or lost
This is the section to act on. Most catastrophic greenhouse failures are not structures that were underrated. They are correctly rated structures that were never anchored properly. 🔩
- 1️⃣ Use the specified anchors, in the specified number, at the specified positions. Substituting tent stakes for ground anchors is not a variation, it is a different building.
- 2️⃣ Anchor into something that resists uplift. Wind does not push a greenhouse over, it lifts it. Gravel needs proper ground anchors or a bolted perimeter frame; pavers and slabs allow direct bolting.
- 3️⃣ Check them annually. Anchors work loose, and a spring inspection takes ten minutes.
- 4️⃣ Keep the door closed in high wind. An open door turns the structure into a pressurized box and is a known failure trigger.
- 5️⃣ Do not remove bracing because it is in the way of a bench. It is in the way because it is doing something.
The base you build determines what anchoring is possible, which is why the two decisions belong together. We compared the options in our foundation guide. 🧱
🛠️ Extra measures for hard climates
- 🧱 Telescopic support braces under the ridge for winter, which raise the snow capacity of an existing structure cheaply and are removed in spring.
- 🌿 A permeable windbreak upwind, hedge or slatted fence, giving useful shelter for roughly eight to ten times its height downwind. Never a solid barrier, which creates turbulence instead.
- 🧹 Clearing snow from the roof with a soft brush from outside if a fall exceeds the rating, working from the eave upward.
- 🔩 Additional glazing clips on the windward face, since panels leaving their clips is a more common failure than frames collapsing.
- 🚪 A door latch that actually latches, and the habit of using it.
🚩 What a missing rating tells you
The most useful test in this entire article costs nothing. 📄
An engineered structure publishes a wind speed and a snow load because it was designed against a load case. A budget kit publishes "heavy duty" and "weather resistant", which are adjectives, not engineering. If a seller will not state the wind rating, they have stated the wind rating. That test, and four others like it, are set out in cheap versus premium greenhouses.
This is also the practical reason ratings matter beyond survival: they are what a permit application needs, and what an insurer or an HOA committee may ask for. 📜
❓ FAQ: wind and snow ratings
What wind rating do I need?
Match or exceed the design wind speed your local building department assigns to your address, then adjust upward for an exposed site. A sheltered suburban lot and an open ridgeline a mile apart are not the same problem. 💨
Will my greenhouse survive a hurricane?
Ratings are design values for sustained wind, not guarantees against a named storm. In hurricane-prone regions, treat the rating as a minimum, follow anchoring specifications exactly, and expect that extreme events exceed residential design assumptions. 🌀
Do I need to clear snow off the roof?
Only if the accumulation approaches or exceeds the rating, or if a snowfall is followed by rain or a freeze-thaw cycle, which adds weight without adding depth. Use a soft brush from outside, working upward from the eave. ❄️
Does a stronger frame mean a lower snow rating is fine?
The frame is exactly what the snow rating measures, so a stronger frame generally means a higher rating. What does not help is thicker glazing, which contributes very little to load capacity. 🏗️
Is polycarbonate or glass better in a storm?
Polycarbonate for impact, decisively, particularly hail. Aluminum-framed glass structures carry the higher published wind ratings in our range. They fail differently rather than one being universally tougher. ⚖️
Can I improve a structure's rating after buying?
You cannot change the published rating, but you can improve real-world survival: better anchoring, winter support braces, extra glazing clips and a permeable windbreak all help materially. 🛠️
🌿 The checklist
Get your local design wind speed and typical snow load from the building department. Shortlist only structures that publish both numbers. Anchor exactly as specified. Add braces if your winters are heavy, and a permeable windbreak if your site is exposed. 🧭
Every model in the Prime Greenhouses range publishes its wind rating and snow load alongside the footprint and ridge height, and a structure like The Peak uses a pointed roof profile specifically so that snow sheds rather than accumulates. 📊