How to secure a garden pergola against very powerful winds?

[David001]

An old wooden seat with a wooden pergola above it (covered with clematis) has over the last 12 years rotted and has also been shunted forwards by gale-force winds, and perhaps by some earth movement, so I have removed the old wooden structure and bought a metal replacement (for just £70 in a sale at Wayfair).

 

Although strong winds will largely blow through the metal-work unobstructed, once the structure is dressed with clematis there will still be some degree of vulnerability in the face of winds.  The vulnerability will be mainly due to the pergola's height being 2 metres and only 1 metre from side to side.

 

So my concern now is how to secure the four feet of the seat so that future gale-force winds striking the pergola from behind will not drive it forwards. 

 

Also, the position where the pergola is to sit is a small flat area of about 2m x 1.5m, behind which the earth rises up a hillside, and in front of which the hillside falls, meaning that it is possible that over time there may be downward, gravity-led, earth movement.  This movement may explain the crack which appeared recently in the thick stone directly in front of the position where the wooden pergola sat.

 

At the end of each leg is a small round horizontal plate, with 3 holes for insertion of the 4" nails which have been supplied.

 

I thought of embedding the feet but it would be best not to lose any of the height of the 4 legs, otherwise the seat will become lower, in relation to the ground.

 

Once the pergola has been secured, I will move the two planters of clematis close to each side and thread the plants through the metalwork.

 

So, how should I go about securing this pergola so that it is stable and level, and so that it is not pushed forwards either by wind or slight earth movement?  What steps should I take?

 

Thank you.

 

David.

 

 

Below: the pergola with the two planters of clematis which will sit close to each of its two sides.

 

 

 

Below: a top-down view.

 

 

 

Below: a crack in the thick stone in front of the seat, possibly suggesting earth movement.

 

 

 

Below: one of the four feet of the structure.

 

 

 

Below: 4-inch nails have been supplied to fasten the four feet.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

[Mr Punter]

Some tent pegs driven at an angle

[JohnMo]

I would be tempted to dig 4 holes (space width square and deep) get some threaded bar, chemical anchor, and postcrete. Fill holes with postcrete and level. Drill holes for flanges. Chemical anchor threaded bar in place. Tighten nuts - it's going nowhere in a hurry.

[Jenki]

15 hours ago, JohnMo said:

I would be tempted to dig 4 holes (space width square and deep) get some threaded bar, chemical anchor, and postcrete. Fill holes with postcrete and level. Drill holes for flanges. Chemical anchor threaded bar in place. Tighten nuts - it's going nowhere in a hurry.

+1 Do this^^^^^^^.. Before living in the Highlands, I would have read this response and thought that's a bit overkill. I read this now and feel the earned experience of Highland living flowing through the advice.🤣

Edited June 22 by Jenki

[saveasteading]

Tent pegs is plenty.but so should be the nails, on angles. 

Plants will catch the wind bug also anchor it.

[Conor]

I'd pave under the area to meet the stone and just fix the pergola to the paving slabs with short concrete screws.

[David001]

On 21/06/2024 at 16:06, JohnMo said:

I would be tempted to dig 4 holes (space width square and deep) get some threaded bar, chemical anchor, and postcrete. Fill holes with postcrete and level. Drill holes for flanges. Chemical anchor threaded bar in place. Tighten nuts - it's going nowhere in a hurry.

@JohnMo, I would be most grateful if you would explain to me the meaning of "Chemical anchor threaded bar in place".

 

I have imagined that it may mean that I should chemically anchor the threaded bar in position, but I don't know what chemical anchoring entails, or what a threaded bar is.

 

Thanks.

 

[JohnMo]

25 minutes ago, David001 said:

@JohnMo, I would be most grateful if you would explain to me the meaning of "Chemical anchor threaded bar in place".

 

I have imagined that it may mean that I should chemically anchor the threaded bar in position, but I don't know what chemical anchoring entails, or what a threaded bar is.

 

Thanks.

 

Drill holes add chemical anchor and then studded bar.wait for 30mins or so, tighten down example below 

 

https://www.screwfix.com/p/rawlplug-r-kem11-175-kit-styrene-free-polyester-resin-175ml/4100R?tc=AE7&gad_source=1&gclid=Cj0KCQjws560BhCuARIsAHMqE0GMQjw3Di4GFty1KU5PXHRqxjYyHvqepGzGGewCciKhOOO8Y1Y_oQYaAqFoEALw_wcB&gclsrc=aw.ds

[saveasteading]

With chemical anchors and concrete bases, the weakness / fail point becomes the tubing of the pergola.

That's why I would use the nails or tent pegs, and let it move a little.

[JohnMo]

43 minutes ago, saveasteading said:

tent pegs,

Ours got lifted in the wind went up and over a 7 ft wall on to the road. But it was the fabric roof that acting as a sail that didn't help. Maybe not such an issue here.

[saveasteading]

40 minutes ago, JohnMo said:

over a 7 ft wall on to the road. 

The decision could be  wrong whichever is chosen.  These tubular things aren't strong. 

 

On 21/06/2024 at 16:21, David001 said:

crack in the thick stone in front of the seat

Don't worry about that. The earth moves a lot all the time.  Edges break off things. Enjoy the pergola. 

[David001]

6 hours ago, saveasteading said:

With chemical anchors and concrete bases, the weakness / fail point becomes the tubing of the pergola.

That's why I would use the nails or tent pegs, and let it move a little.

@saveasteading, the pergola in the pics above involves solid metal parts only.  They're not hollow.  But of course I don't know how strong the metal is.  A roofing contractor here today advised me that lot of these structures are made from recycled metals and that while they may be "solid metal" the metal itself may not be as strong as it was in its first incarnation.  I don't know if that's true or not.  Anyway, I take your point that if the feet are absolutely fixed to concrete then any give will have to be in the pergola above.

[SteamyTea]

On 05/07/2024 at 18:23, David001 said:

don't know if that's true or not

I do. It will be made to the specified standard requested.

On 22/06/2024 at 08:32, saveasteading said:

Tent pegs is plenty

An old college mate of mine was a rigger for Moscow State Circus. He put lots of tent pegs in.

He was also, at the same time, an arm wrestling champion (75kg).

 

Edited July 7 by SteamyTea

[joe90]

1 hour ago, SteamyTea said:

An old college mate of mine was a rigger for Moscow State Circus. He put lots of tent pegs in.

Yes but they are not 4 inch nails, more like 2 ft inch thick bar.

[SteamyTea]

1 minute ago, joe90 said:

more like 2 ft inch thick bar.

Whacked through tarmac and concrete carpark.

No wonder he is so strong.

He is the little fellow on the right.

 

[Roundtuit]

A couple of suggestions;

- whack some lengths of thick re-bar in and wire the pergola to that.

- plant the clematis in the ground; it will hold the pergola in position once it's established.