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How to build pergola footings?

Hi,

I would like to install the pergola using the pergola kits, like this

Double Wall Mounted Pergola Kit with Shade Sail for 90x90 Timber Posts – Modaprax

To do that, I need 3 x concrete footings. I am thinking to remove grass and make footings.

1. How big/deep would you recommend?

2. Do I need to put gravel first and concrete?

3. Do you recommend rebar?

4. How to make sure 3 footings are level with each other so that the pergola is also level?

Please share your knowledge/experience

Thanks

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Comments

MitchellMc

Hi @dogbural,

You’ll need to reach out to the manufacturer of that pergola kit to confirm the exact footing specifications. Most manufacturers provide recommended footing sizes and installation requirements for their systems.

It’s also important to keep in mind that footing sizes can vary depending on your local soil conditions and the wind rating of your area. For that reason, it’s best to check with your local council first. The pergola may fall under the size limit that doesn’t require approval, but if approval is needed, the footings will have to comply with the building code for your region.

We do carry a similar system called TOJA Grid and if you’re interested in that option, I’d be happy to help find the footing specifications or provide advice on using it. However, since the Modaprax system differs, your best source of accurate information will be the manufacturer directly.

It’s common practice to add a layer of compacted gravel, around 100mm thick, at the bottom of each hole to help with drainage before pouring concrete. Adding a short section of rebar or a reinforcing cage through the centre of the footing can improve strength, especially in softer soils. To make sure the three footings are level with each other, you can run a string line or use a laser level across the footing locations to mark consistent height points before pouring the concrete. Once set, this will ensure the pergola sits level across all posts.

These are general guidelines only, so I’d recommend confirming the exact footing requirements with the pergola manufacturer or your local council before starting the project.

Please let me know if you have any questions.

Mitchell

dogbural

https://www.workshop.bunnings.com.au/discussion/comment/58569#Comment_58569

Hi @MitchellMc

Now I decided to just build the pergola in a tradition way.

I have gone thru threads in this workshop but I still have some questions.

So, now the size of the freestanding pergola I am thinking is 3M x 1M.

Below is my selection of timbers

For post (x 4) : 125 x 125mm 3.0m Post F7 Cypress Sawn - Bunnings Australia

For beam (barrier) (x 2) : 190 x 45mm Outdoor Framing H3 Treated Pine 4.2m - Bunnings Australia

For rafter (x 6) : 140 x 45mm Outdoor Framing H3 Treated Pine - 4.8m - Bunnings Australia

The post will be mounted on the anchor (Pryda Post Anchor High Wind 600 x 125mm M12 - Bunnings Australia).

Q1. Is my selection of timbers suitable or overkill? Especially, for the 3000 mm long beam, is it okay for them to be supported from both ends only?

Q2. When connecting beam to post, From what I searched, the notching on the post would be best way, but I do not think I am not that skillful. Is just bolting them directly to the post using cup head bolts enough? If so, how many and what size of bolts should I use?

Or should I use a bracket like suggested in this thread (What kind of brackets to use to connect ... | Bunnings Workshop community)?

Or just combine both?

Q3. I would like rafters to be overhang on the beam, I wonder how much the rafters can be overhung? I am thinking that one side is 300mm; while the other end 600mm? I will probably put battens only on top.

Q4. How can I joint the rafter to the beam? Do you recommend a notch on rafter? Once the rafter is sitting on the beam at notch, should I just bolt it down from top of the rafter to the beam? Or is there any joist hanger that does not require a notch?

Thanks

MitchellMc

https://www.workshop.bunnings.com.au/discussion/comment/92954#Comment_92954

Hi @dogbural,

You are on the right path, and your timber selection is solid rather than excessive. The 125 x 125 cypress posts are a good choice, and the 190 x 45 beams spanning 3 m and supported at both ends should be fine for a pergola of this size. The 140 x 45 rafters are also more than adequate. However, as with any structure like this, it would be best to run your plan past a builder or your local council for verification.

Notching the posts for the beams is the strongest method, but if you are not confident, bolting the beams directly to the posts is acceptable. Use two M12 galvanised cup head bolts per post connection with large washers. If you want extra reassurance, adding a structural bracket as well is fine, especially in windy areas.

A 300 mm rafter overhang is very comfortable, and 600 mm is still acceptable with your rafter size, provided everything is well fixed. For fixing rafters to beams, sitting them on top of the beam and fixing them down with two galvanised structural screws per rafter is a simple and reliable option. A notch is not essential, and joist hangers are generally unnecessary for this style of pergola. Another option is to screw through the face of the beam into the ends of the rafters.

Please let me know if you have any questions.

Mitchell

dogbural

https://www.workshop.bunnings.com.au/discussion/comment/112641#Comment_112641

Thanks @MitchellMc

I have just been delivered of 190 x 45mm for beams from bunnings.

Noticed that one of them has knothole (like dia 20mm), do you think i can still use this for a beam?

MitchellMc

https://www.workshop.bunnings.com.au/discussion/comment/123922#Comment_123922

The timber has been structurally graded, and knots are taken into account when the timber is assessed and stamped @dogbural, so from a structural point of view, a single knothole around 20 mm in diameter isn’t going to compromise the beam’s load-carrying capacity for a pergola. In other words, it will still perform to the rating it was sold under.

Where it can be an issue is visually. A noticeable knothole in a beam that’s on show isn’t always what people expect when they’re purchasing larger structural members. If it’s going to be visible and you’re not happy with the look, I’d suggest contacting the store you purchased it from and asking if you can swap that length over. That’s a pretty reasonable expectation, especially if the timber is otherwise unused.

So structurally you’re fine to use it, but aesthetically it comes down to whether you’re happy with how it’ll look once installed.

Mitchell

dogbural

https://www.workshop.bunnings.com.au/discussion/comment/131340#Comment_131340

Thanks @MitchellMc - I have ended up having it replaced.

I have another question regarding bolt length and pilot holes. For attaching the post to the wind stirrup, I will use M12 cup head bolts.

Dimensions:

Post: 125mm
Stirrup thickness: 10mm (5mm each side)
Washer (for nut): 3mm
Nut: 10mm

Based on these measurements, is a 160mm bolt too tight? If I use 170mm, is it common to cut off the excess thread or cover it with a cap to minimise the hazard?

MitchellMc

https://www.workshop.bunnings.com.au/discussion/comment/135863#Comment_135863

All up, that's 148mm, so I see no reason why a 160mm bolt won't work @dogbural. That will leave approximately 10mm exposed, which can be trimmed. Just remember that you may need to remove sharp burrs with a metal file after cutting. I'm not aware of any specific caps for covering exposed bolt threads.

Mitchell

dogbural

https://www.workshop.bunnings.com.au/discussion/comment/138954#Comment_138954

Hi @MitchellMc

I just put the post on the wind stirrup and realised that the post does not seat flat on, there is a gap between the stirrup and the bottom of the post due to weld( or fillet) at corner.

How can i fix this? Do i undo and ground corner of the bottom post? Please advise.

JacobZ

https://www.workshop.bunnings.com.au/discussion/comment/141031#Comment_141031

Hi @dogbural,

The easiest thing you can do is disconnect the post and cut it so that it fits around whatever is impeding it. You want as much of the bottom of your post sitting firmly on that stirrup as possible so that the weight transfer is as even as possible.

Let me know if you have any further questions.

Jacob

dogbural

https://www.workshop.bunnings.com.au/discussion/comment/142573#Comment_142573

Thanks @JacobZ

Do you think i can use the same holes that i made for the 1st trial? The holes will be bigger now. Or i need to rotate the post to 90deg? What do you recommend?

EricL

https://www.workshop.bunnings.com.au/discussion/comment/143672#Comment_143672

Hello @dogbural

Would it be possible for you to post a photo of the post with the nut and bolt installed? How loose is the installation of the post? If it is too loose, it would be better to drill new post holes.

Let me call on our experienced members @Dave-1, @AlanM52 and @Nailbag for their recommendations.

If you need further assistance, please let us know.

Eric

Dave-1

https://www.workshop.bunnings.com.au/discussion/comment/144499#Comment_144499

Good Evening @dogbural

I have just read through the thread 🙂 So I think I am up to speed.

A photo would be good for sure and we would be able to give a better suggestion on what the next step is.

A couple of in between questions tho.

-Are you planning on leaving a gap below the post and above the stirrup? (It helps prolong the life of the post as it stops it sitting in water)

-Have you drawn up a sketch of what you are doing? I find a sketch helps overall to picture how things will look and also smaller sketches of "points" such as what you are working on atm.

-Do you have some extra bits of timber (longish, maybe 1.8m) to use as temporay supports once you bolt the post in place?

Looking at that last pic that you posted, you may need to use a chisel and take off 5mm or 10mm to get the post to fit. Not sure where you are up to so will wait for confirmation 🙂

Dave

AlanM52

https://www.workshop.bunnings.com.au/discussion/comment/141031#Comment_141031

Hi @dogbural,

Looks like you are holding the post on a angle so it's not sitting flush on the stirrup.

@Dave-1 mentioned you may need to chisel off to get it to fit but I think it's a lot more that that.

We really need another photo a bit further back and I am thinking you need to swap that stirrup with one that correctly fits the post.

Cheers

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