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Laminating plywood for pergola rafters

Does anyone have experience with laminating plywood for use as rafters in pergolas? I have half a dozen 5m lengths of bent 70 by 40 timbers (3x1 1/2 in old speak I think). They've been bent in the rain and humidity and bunnings threw them in a $5 bin. i've clamped them to make their crescent bends uniform. I want to concrete in a couple of steel posts and beams and create sale effect with the bent rafters suspended by the centred posts.

But I think the 70x40 are too small for rafters. So I wondered if I could bolster them sufficiently by encasing them in ply? Ultimately, I need to have some plans for council, but maybe someone in the community has advice.

brian

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Jason

Hi Brian (@ub_268)

Thanks for making your first post. I've moved it so it's a new discussion and is more visible to other community members. I trust members will be able to provide some suggestions for you.

Let me also extend a very warm welcome to the Workshop community. We look forward to seeing how this project progresses, as well as reading about other projects and plans. Please feel free to post anytime you need a hand or have something to share. And please let me know if you ever have any feedback about how we can improve Workshop for you.

Thanks again,

Jason

redracer01

Hello @ub_268

Would it be possible to post a sketch of your idea? Perhaps a photo of your drawing? Where it is to be located?

ub_268

https://www.workshop.bunnings.com.au/discussion/comment/5463#Comment_5463

Here are a few pics of the site including a profile of the bent 3 by 1 1/2s. There's a gap of about 180mm from top of the arch of the sticks to a line of 4.7m connecting the ends of the sticks.

ub_268

https://www.workshop.bunnings.com.au/discussion/comment/5463#Comment_5463

I think my first post of the drawings failed. So, I extend thanks again to the warm welcome I've received from the workshop community.
Let's try to upload those drawings. One is a side elevation with scale of 1:25 the other an isometric sketch with scale 1:50. My son-in-law has estimated the slope to be 26 degrees at its perceived max according to his iPhone app. I've used a figure of 21.8 degrees to provide an easy measure of 2 up for 5 across.

Jason

https://www.workshop.bunnings.com.au/discussion/comment/64865#Comment_64865

Thanks for sharing the photos and sketches @ub_268.

I'm sure they will help @redracer01 and other community members get a much better idea of what you are working with and enable them to provide more specific advice.

We are looking forward to seeing how the project progresses.

Jason

redracer01

https://www.workshop.bunnings.com.au/discussion/comment/64865#Comment_64865

Hello @ub_268

Have been reading up on lamination and I believe that what you are planning is possible. I do have a few concerns about this project you are about to begin.

1. Any material you use would have to be for oudoor use. If you are laminating or covering it in plywood, it would have to be marine ply and it would have to be heavily protected with paint to withstand the elements.

2. It would have to be structuraly sound. I'm not an engineer and in this instance I would recommend you speak to @BIM_Engineer who has years of experience concerning this matter. Perhaps he can give you better advice about laminating timber together.

3. If you do glue them together you would have to use an "exterior non water based" glue to avoid warping and shrinkage.

Other than those concerns, I find your project quite amazing and think it would look fantastic once finished. My knowlege of laminating timber together for outside use is a bit limited. There is always the internet and the many videos on it concerning lamination and timber joinery. Calling on our timber experts! Good luck and hope to see your finished project on the community board.

BIM_Engineer

https://www.workshop.bunnings.com.au/discussion/comment/64865#Comment_64865

Interesting design and thanks for the photos/sketch

The image/Structure, that comes close, that I can think of are

cantilever Bus Shelters they are all built out of Steel

Wind Loading is a factor in the choice of building materials

and the councils Building department will require an engineers design/certification

BTW if you are into Repurposing, ask your council what they do with old shelters that are replaced

The would be easily and cost effective to modify

Goodluck

ub_268

https://www.workshop.bunnings.com.au/discussion/comment/95108#Comment_95108

Thanks for the advice and ideas BIM. I'll see if there's anything like those shelters recycling about the place.

brian

BIM_Engineer

https://www.workshop.bunnings.com.au/discussion/comment/114078#Comment_114078

They are usually at the Councils depot
It's a good excuse to buy a 3-1 Welder-Plasma Cutter
Cheers

ub_268

https://www.workshop.bunnings.com.au/discussion/comment/124716#Comment_124716

Thanks everyone for encouragement regarding my pergola idea. I've been busy terracing the slope from the bottom up. I can see why this wasn't done by previous owners! I'm using 200 by 75s (8 b 3s) recycled hardwood and the specs in the attached pdf as a guide, as well as listening to people. the concern is the specs say it assumes a slope of no more than 1 in 6. My slope is more like 1 in 2.5! Even 0.8 in 1.5! About 22 to 28 degrees not 10 degrees!
Does anyone know about no-fines mix? It's a mix of cement and aggregate only. No, or very little sand. It remains porous. It's encouraged by the Allan Block system. But it sounds like it might be good for my post footings as well. I'm also wondering if I can make up my own mix of copper sulphate to use along with linseed oil for the timber.
Any thoughts?

ub_268

https://www.workshop.bunnings.com.au/discussion/comment/124716#Comment_124716

Sorry, I couldn't find the upload document link for the retainer wall specs. Basically, I'm working on maximum wall heights of 800-900mm and a minimum of 1.5 m between retainer walls (though I thing it's given in a formula in the specs I think) and about 1.2 m between posts in the wall and placing two posts in a right angle orientation at the corners. Depths, using hardwood, isn't quite as much as the post is above the ground. The drainage will take some digging.

BIM_Engineer

https://www.workshop.bunnings.com.au/discussion/comment/131895#Comment_131895

I suggest you get clarification on the different retaining wall systems and Calculation requirements from your Council Building Department
Generally, the Council will require plans, Elevations,spot levels, Engineering Details,notes, calculations and certification.
.eg here

Post & Rail Retaining wall BIM Details & Notes hth

ub_268

https://www.workshop.bunnings.com.au/discussion/comment/136248#Comment_136248

Thanks BIM. I posted the web page that I think you're alluding to in your uploads. Unfortunately, they didn't come out well. But the thread is pretty old now.
Can you help me again? I've concreted in 1 and half of my three-post retainer wall tiers that I'm doing on that slope, as I try to work from the lower level to the upper where I want a pergola. And I'm happy with the no-fines mix. (How do I upload a photo?)
What I'm keen to do, not wanting the other side of the drive to feel left out, is to build an elevated den abridging the upper terraced garden and the space over and beyond the existing retainer wall. I'd send you elevation plans and photos but I can't remember how I uploaded last time. I'm thinking I could implant two posts into the lower terrace and two into the top terrace and construct the framework on those for a 3 by 3 structure. The taller pair of posts would be 2.5 m above ground level.

Jason

https://www.workshop.bunnings.com.au/discussion/comment/139216#Comment_139216

Hi @ub_268,

Photos will help @BIM_Engineer and other community members better understand what you are working with, so I certainly encourage you to add them to your posts.

To add photos to a post, make sure you use the red reply button to access the post editor.

Then you'll find you can press the Photos button or the Upload Images button (either is fine). You can add as many images to a post as you like.

Please let me know if you have any trouble.

Jason

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