ᐅ Foundation for a 3x3 meter pergola

Created on: 5 Apr 2023 10:54
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Peter Silie
Hello,

I am a bit uncertain about the foundation for a 3x3 meter (10x10 feet) pergola. We have a terrace with floating but very firmly fixed concrete pavers (about 4 cm (1.5 inches) thick). Setting aside all general recommendations for a moment, would you still insist on building a foundation of 30 cm x 30 cm x 40 cm (12 x 12 x 16 inches), or do you think the pergola could also be stable directly on the pavers? Alternatively, we are considering removing the affected pavers, excavating the gravel base, pouring a 10–15 cm (4–6 inches) thick cement mortar layer, laying the pavers into the mortar bed, and then anchoring the pergola into this new slab. The pergola is generally well protected from the wind and located close to the house. It will be made of powder-coated aluminum, so it is quite heavy.

Thanks for your advice and best regards
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Peter Silie
5 Apr 2023 13:47
Tolentino schrieb:

Yes, with a roof you need proper foundations. The suction forces caused by even a small storm are incredible.
Axel tore down our pavilion at the beginning of the year and the wind gusts only reached 79 km/h (49 mph). That’s actually nothing.


The thing will weigh almost 200 kg (440 lbs). When the slats are open in a storm, do you really think it still won’t fly away?
Tolentino5 Apr 2023 13:57
I wouldn’t take the risk. Do you always remember to open the slats (which then provide lateral resistance)? A ship weighs several tons and is easily moved by the wind. There’s a reason why sails are reefed in strong winds.
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WilderSueden
5 Apr 2023 14:10
Peter Silie schrieb:

The thing weighs almost 200kg (440 lbs). When the slats open during a storm, do you really think it still won’t blow away?

3x3m (10x10 ft) equals 9 square meters (97 square feet). If it’s positioned perpendicular to the wind, you already have enough wind pressure from wind force 7. Even if it’s sheltered facing the main wind direction... during thunderstorms, wind force 8 often occurs, and near buildings you also have to consider wind turbulence and other effects. You can install the footing pads in one day’s work.
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Peter Silie
18 Apr 2023 15:19
The assembly went well overall, but now two screws have broken. They are 10cm (5 inches) screws, inserted with wall plugs. Based on experience, does this usually hold, or should the screws be removed? Unfortunately, I can’t reach them as they broke about 2-3cm (1 inch) below the surface.
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Osnabruecker
18 Apr 2023 16:13
Peter Silie schrieb:

The assembly went well

Or
Peter Silie schrieb:

now only two screws have broken.

At least you now have a designed weak point, so the foundation will hold during storms.

How many screws are there in total? 2 out of 4? 2 out of 16?
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Peter Silie
19 Apr 2023 11:15
two out of 12.

The anchors are fully inserted, the screws are about 3/4 into the anchors. Father-in-law says, "That will hold" 😀, but I’m more cautious—always safety first.