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Pergola Post - Notch it or do not notch it?

Hey All,

We are planning to build a freestanding pergola 2.2 m X 2.7 m. We got timber delivered from Bunnings about a month ago. I am in process of preparing things to get rolling.

1. We had concrete apron poured around our house and we had to extend this concrete slab in order to mount pergola posts on it.

2. We are thinking to use Chemset 501 to secure the anchor and then put bolt down stirrups. (I had to read multiple articles online to decide on whether Chemset or Dynabolts). I had to make a call based on what I read. Please feel free to add your inputs and share your experiences in this regards.

3. I had to level the previously poured concrete slab so that when I install bolt down stirrup it does not go inclined (as concrete is poured to make water run away from building). We used Dunlop construction grout about 20mm to make it a flat and level surface for stirrup.

4. Now looks like I have hit another hurdle. We have Cypress posts of 125 X 125 and 2.7m in length. Beam of TP 240mmX45mm (2.2m length post to post). I am planning to use 3 Bolts M10 X 150mm or +220mm Cup bolts (based on notch it or not) to secure beams to post.

5. We have Rafters 140X45 and Louvers 90 X 45 to be sitting on beams.

What are you recommendations on securing / mounting beams to the posts? Is notching good or it weakens the posts?

Kindly share your experiences and inputs.

Thanks in advance.

Stallone

Side view.When you look straight at the postTopview before notching

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Comments

MitchellMc

Welcome to the Bunnings Workshop community @stallone. It's great to have you join us and many thanks for your questions.

If done correctly notching a post does not weaken it as the load is transferred down through the post. Notching posts is not only done because it looks great but it also stabilises the beam.

You might be interested in checking out the very knowledgable @ProjectPete's Poolside timber cabana build. He not only notches out his posts but creates a double rebate join on the post for the beams.

You should find this step-by-step tutorial helpful: How to build a pergola. You'll note that we have chosen to notch our posts as well.

Notching posts is a building technique that has been used for thousands of years and if done correctly can strengthen the structure significantly.

Please let me know if you need further information or had questions.

Mitchell

ProjectPete

In short, not away. As @MitchellMc said, the load is transferred through the post.

Think of giving your kids a shoulder right versus carrying them like a shopping bag. Or how we naturally throw a big of cement or length of timber over our shoulder rather than carrying like a shopping bag. Which is easier? Which load is easier to bear?

stallone

Yeah! thank you @MitchellMc and @ProjectPete for you inputs. I think it makes a lot of sense to make notch and then mount the beams.

Is there are rule of thumb that once the beams are mounted it should sit flush? or it can have an over hang about 10 to 15 mm?

Example

1. Beams are 45mm

2. Posts are 125 mm

3. I am planning to have 2 beams (like the way I have showed in side view image attached to my first post).

4. Now If I notch 45 mm on with side of the post then I will eat up 90mm and I post will have only 35mm left at the place of notching.

5. Would 35mm on post be enough or be strong enough to hold 3 M10s, wind etc. Overall strength.

6. From point number 4, I just notch it 30mm on each side and I will eat up 60mm only against 90mm (in step5). I will still have 15mm overhanging when I mount the beam but I think its weight will anyways be already transferred to the post as it will have more than 50% of its body mounted onto post.

Let me know your thoughts. I am a vaguely remember reading strength of materials during my engineering days (13 years ago 🙂 ) and later moved into software side of things.

So please forgive for the terminologies used here if they are unclear. I will try to draw it if needed.

Thank you!

MitchellMc

https://www.workshop.bunnings.com.au/discussion/comment/10692#Comment_10692

@stallone,

The beam does not need to sit flush with you post, in fact, you could have only one-quarter of the beam notched in as long as it is bolted securely. Just remember you don't need to notch in at all. I also do not think you are eating up too much of the post with the mounting. You might like to notch in slightly less to leave more of the post.

Mitchell

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