How to create the concrete footings using embedded post anchors for an arbour?

[BeginnerPaul]

Good Evening Folks

I would like to construct a small arbour say 2metres by 3 metres and 2 metres high. Posts say 90x90

This question is about creating the right footings for the post anchors

Am considering post anchors which will be embedded in concrete

Pryda 200 x 90mm M10 Full Stirrup Solid Stem Post ...$16.31Add to Cart

Question is what are the right dimensions for the concreted hole which will have the post holders embedded

All advice welcome

[JacobZ · Accepted solution]

Hi @BeginnerPaul,

Thank you for your question and welcome to the Bunnings Workshop community, it is fantastic to have you with us.

While it is fairly unlikely you'd require building approval, I'd suggest you start by contacting your local council to confirm this. Rules vary from region to region, and it is always better to be safe than sorry. A quick phone call to confirm this can save you a lot of pain further down the line.

It is hard to give definitive answers to this question as structures like arbours are subject to a number of variables that can alter footing design greatly depending on things like the wind rating of the area and the soil quality. If you want a definitive answer, you will need to contact an engineer for their assistance in designing a suitable footing. They will be able to use the Pryda Post Anchor Design Guide to design footings that are suitable for your arbour.

With this being said, footings that use post anchors are generally 300mm in diameter and at least 600mm deep. I would suggest using a high wind anchor such as this Pryda Post Anchor High Wind 450 x 90mm M12 as opposed to the one you've linked to above.

Footings can be dug with a Post Hole Digger which has a 300mm auger that is designed for this exact purpose.

Let me know if you have any further questions.

Jacob

[BeginnerPaul]

Thank you JacobZ

The Arbour will be small - say 2m x 3 m.

Ideas on how to align the 4 posts properly?

[JacobZ]

Hi @BeginnerPaul,

Setting everything out before the project commences is the best way to make sure everything aligns. 

Have a look at How To Set Out A Deck for some guidance on setting out your project.

Start by selecting the post that is most important in terms of alignment. There may be a garden bed or fence line that you can measure off to ensure it is placed correctly. Working from this point, you can mark out the general area with marking paint.

You can then construct hurdles from scrap timber and star pickets. These should be low enough to the ground that string lines will run right by the anchors when they are set in the concrete.

You should then use the 3-4-5 method to ensure the string lines are perfectly square to each other. Measure everything 2-3 times and make small adjustments where necessary. 

If you need your anchors to be level with each other, you can use a Line Level, making slight adjustments to the height of your hurdles to get everything nice and level. This step is not 100% necessary as you can always cut the top of your posts instead of having the bottom of them perfectly level.

You can then use How To Install Stumps as a guide for installing your anchors. You should use a torpedo level to ensure your anchors are plumb when they are installed.

Plumbing the anchor will make sure they are plumb in one direction, but as the anchors have an open and closed side, you will still need to check for plumb when installing the posts.

After the posts are installed, checking for plumb, level and the distance between posts as you move higher into the construction will ensure everything is aligned at the top of the posts as well as at the bottom. With each new addition to the structure, measure distances between posts and check for plumb and level. 

Let me know if you have any further questions.

Jacob

[BeginnerPaul]

Thank you JacobZ

The small arbour  2m x 3m is of simple design

Are there videos which would be useful?

Regards

Paul

[JacobZ]

Hi @BeginnerPaul,
 

How To Build a D.I.Y. Timber Garden Arbour has a video that should come in handy, but it is not exactly the same size as the one you have planned.

The video in How To Install Posts For a Picket Fence would also be handy for some guidance on setting your posts and anchors.

Also, alot of the principles used to build a deck would come in handy for your project. There are a number of videos in How To Build A Deck that would be useful.

I am sure if you have a look on Youtube you will be able to find similar projects that you can follow along for guidance.

Also, remember the Workshop community will always be here to help if you run into specific questions along the way.

Jacob
 

[BeginnerPaul]

Thanks JacobZ. That has been very useful.

Questions now about fixing the 3m long bearers (150 x 50)  to the 90 x 90 posts:

Are coach screws the most appropriate? 

What size coach screw is right to connect the two pieces?

1 or 2 at each end?

How to use a power drill to drive the coach screws?

Thanks

Paul

[MitchellMc]

Hi @BeginnerPaul,

Coach screws or cuphead bolts can be used. Using bolts would be the best option as they provide significant compression to the joint.

These ZENITH M10 x 150mm Hot Dip Galvanised Cup Head Bolts & Nuts would be sufficient for the 50mm bearer and 90mm posts thickness.

I would suggest two at each end.

With your power drill, you'll drill a 12mm hole through the bearer and post. Then, you insert the bolts, washer, and nut before tightening them with a spanner.

I just wanted to point out that 3000mm is fairly long for 140 x 45mm to span. You should check timber span tables to ensure it is of an appropriate calibre for your project. 

Please let me know if you have any questions.

Mitchell

[BeginnerPaul]

Thank you Mitchell for your advice

I could have mentioned that two bearers are planned on either side of each post

For bolts that would be a total depth of 50mm plus 150mm post and 50 mm say 250 Wonder what size bolts would be appropriate?

Where would I find a relevant timber span table please?

Regards 

Paul

[MitchellMc]

These ZENITH M16 x 260mm Hot Dip Galvanised Cup Head Bolts & Nuts should do the job @BeginnerPaul.

Mitchell