A terrace roof cannot pick its weather. It will meet autumn storms, wet snow, hail and summer squalls — and it will meet them alone, in the open, for decades. So before you compare colors and sizes, it is worth understanding the two numbers that describe how a pergola handles all of that: wind resistance and snow load. This article explains what the ratings mean physically, what our numbers are, where they come from, and the handful of practical habits that keep you comfortably inside the limits without ever thinking about them.
Wind: what 110 km/h actually means
Our pergolas are engineered for wind speeds up to 110 km/h. Numbers need context, so put it on the Beaufort scale: 110 km/h corresponds to force 11 — a violent storm, the kind that gets a name, closes bridges and leads the evening news. For comparison:
- Force 6 (39–49 km/h) — a strong breeze; umbrellas struggle. Ordinary blustery Dutch day.
- Force 8 (62–74 km/h) — a gale; twigs break from trees, walking is hard work. A serious autumn front.
- Force 10 (89–102 km/h) — a storm; trees are uprooted, structural damage begins on weak buildings.
- Force 11 (103–117 km/h) — where our rating sits. Widespread damage territory for unengineered structures.
Day-to-day coastal wind, even the stiff force 7 that empties beaches, operates far below the structural limit of the pergola standing calmly in your garden.
Where the wind rating comes from
A rating like this is a property of a complete system, not a thick post. Four things work together:
- The frame. A 13.5 × 13.5 cm post profile with 2 mm aluminum walls resists bending; box profiles of this size are enormously stiff for their weight.
- The connections. Engineered corner connectors transfer loads between beams and posts so the frame acts as one rigid body rather than four sticks. Corners are where cheap structures fail first.
- The anchoring. Every post is bolted to a solid base — concrete, stone or a robust deck. The rating assumes this anchoring, which is why the installation guide is so specific about it. An unanchored pergola is a kite with furniture under it; a bolted one is a building.
- The louvers. The slats sit in the mechanism under tension — they do not rattle, lift or chatter in gusts.
One practical tip that surprises people: in very high wind, a slightly open louver position is often the friendliest configuration. Air passes through the roof instead of pushing against a sealed surface — the same reason you crack a window during a storm rather than letting the door slam. It's not required by the rating; it's just good seamanship for your garden.
Snow load: kilograms per square foot, demystified
Snow load is expressed in kg/m² — how much weight each square foot of the closed roof can safely carry. The number matters more than people expect, because snow is deceptive:
- Fresh powder is light: roughly 1 kg/m² per centimetre of depth. Ten centimetres ≈ 10 kg/m². Harmless.
- Wet, settled snow — the kind the coast actually gets — is three times heavier or more: 10 cm can weigh 30+ kg/m².
- Refrozen slush and ice is heavier still. This is the load case ratings exist for.
Our numbers: the manual Pergola Piano carries 65 – 120 kg/m² depending on size. The electric Equa carries 160 – 320 kg/m² per size — the compact 10-foot-wide sizes rate highest (320), the 13-foot widths carry 160, because louvers spanning shorter distances simply carry more. The exact per-size table is published on each product page. Even the lowest number in the range — 65 kg/m² — represents twenty-plus centimetres of wet snow, which is a memorable winter event at open ground.
The one winter habit worth adopting
Here is what makes the snow numbers almost academic in practice: when heavy snowfall is forecast, tilt the louvers to the vertical position. Snow falls straight through instead of accumulating, and the load question disappears entirely. It takes a few seconds — a few turns of the crank on the Piano, one press of the remote on the electric models — and it is the single best thing you can do for the roof in winter. The louvers themselves are unbothered by frost, ice and cold; aluminum and the powder coating are rated for it all.
If snow has already fallen on a closed roof, don't worry, that is exactly what the rating is for — but avoid opening the louvers under a heavy load; brush or let melt first, then operate.
Rain, hail and everything else
For completeness: rain is handled by design — closed louvers drain through the integrated gutter and down through the posts, at genuinely stormy rainfall rates. Hail bounces off powder-coated aluminum without cosmetic drama, which is more than garden glass roofs can say. UV, salt air and frost cycles are what the coating and alloy were specified for. The pergola's whole job description is standing outside.
What this means when you choose
For a sheltered urban or suburban garden, any model in the range is comfortably within its limits and the ratings should not steer your choice — pick on roof type, size and features. Lean toward the higher-rated electric models, and mention your situation in a quote request, if any of these apply:
- Open open farmland or field exposure with a long wind fetch and nothing to break it
- First line at the coast or on exposed high ground
- Roof terraces and upper floors, where wind speeds run meaningfully higher than at ground level
- Inland locations that reliably see real snow accumulation each winter
We factor exposure into the advice — sometimes the answer is simply "the size you wanted, one width narrower, rates twice as high for snow."
The bottom line
Engineering numbers are not marketing; they are the reason you can leave the pergola out in January without a second thought, and the reason a violent-storm warning on your phone is weather news, not furniture news. Compare all three models' ratings side by side in the table on every product page, read how the louvered roof works, or take the quiz to get a recommendation matched to your garden.