pergola foundations

[Chopstick]

My neighbour is paying a guy to build a pergola for him and was telling me the other day what he is doing and I wanted to check people opinions about the foundations.
When I built mine we put in 600x600 foundation slabs with steel stirrups in them as per recommendations from the Staines book.
However this guy is talking about bolting stirrups directly to the existing concrete patio which is just normal thickness pattern paved concrete (8-10cm thick). The area is about 5-6m wide by 8m long so although it is a fair area of concrete beneath it I just worry about whether it has the 'structural' strength necessary to be used in this manner.

Anyway, any advice or opinions appreciated, hopefully you all tell me its fine as I am not sure how to broach it with him if it isnt.

[Barry_White]

Hi Chopstick

If it is a pergola with no cladding on top that would be no problem as all he would have is deadload, and the concrete would be able to sustain it.

If it is actually an awning which has a roof that is a different kettle of fish because the wind loading is far greater than the dead load both downward pressure and the upward pressure is far stronger.

There is a lot of variables and if the building is surrounded by other buildings this provides protection from the wind to a certain extent.

I have seen a lot of carports and awnings built with the posts just bolted down to the 4" concrete with just Dynabolts without any problems.

It is usual to have a pier at each post to increase the holddown strength.

If it was me putting it on an existing slab I would be using a plate about 150mm square with a hole in each corner and use chemical anchors to hold it down.

Bear in mind this would only be neccessary if it had a roof on it, if it is just an open pergola it would be fine as you desrcibed.

The other important thing is he using a licenced builder or contractor to do it. If it is a mate thing he is carrying all the risk and the other thing has he got council approval for it. As I said there is so many variables.

[Jon]

I have had a 5m * 6m steel pitched roof awning done in Sydney by an awning company and they just bolted brackets to the existing 4" slab. Got passed by council no probs.
Mind you, I found that the installer had forgotten to fix the posts to the anchors so it was only it's own weight holding it down but I fixed that.

Jon

[Dave Mows]

I am from the states. I am slowing figuring out that this site is Australian. lol Question: Is pergola more popular in Australia. I have noticed that it is something to have in Australia and growing more and more popular here.

[Barry_White]

I am from the states. I am slowing figuring out that this site is Australian. lol Question: Is pergola more popular in Australia. I have noticed that it is something to have in Australia and growing more and more popular here.
Hi Dave

Having been in the building industry for the last 35 years I would consider the pergola the most useless piece of construction ever devised for the Australian climate unless you want to grow some sort of a vine on it.

The only problem with that is most sorts of vines will slowly destroy the pergola anyway if they are made of timber. They also get dry rot in them, even ones made from good old Australian hardwood.

If I was going to build a pergola for a vine I would build it out of steel and then at least it would last.

My latest occupation that I have taken up is selling Spanline Awnings and probably 50% of the Awnings we sell we remove a useless dry rotted pergola that is usually attached to the house, as well the customer has to cut down the vine.

A lot of people grow the vine over the pergola to provide shade in the summer time. The other problem with this is if they are disiduous in the autumn you have leaves everywhere and if they aren't disiduous in the winter you have moss and algie growing on the your paving or your timber deck and as well it will speed up the rotting progress of the timber deck.

Apart from that you have no weather protection to sit out in the open on a wet day.


Just my 2 cents worth.
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[Dave Mows]

Where did pergola designs come from anyway?