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Laminating plywood for pergola rafters

ub_268
New Contributor

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

Community Manager Jason
Community Manager

Re: Laminating plywood for pergola rafters

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

 

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redracer01
Experienced Contributor

Re: Laminating plywood for pergola rafters

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
New Contributor

Re: Laminating plywood for pergola rafters

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.bent3b1_5s.jpg

 

SlopedSiteViewedFromHighPoint.jpg

 

SlopedSiteViewedFromLow.jpg

 

ub_268
New Contributor

Re: Laminating plywood for pergola rafters

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.IsometricSketchOfPergolaConcept_.png

 

SideElevationOfPergolaConcept.png

 

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Community Manager Jason
Community Manager

Re: Laminating plywood for pergola rafters

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

 

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redracer01
Experienced Contributor

Re: Laminating plywood for pergola rafters

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
Valued Contributor

Re: Laminating plywood for pergola rafters

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
New Contributor

Re: Laminating plywood for pergola rafters

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

brian

BIM_Engineer
Valued Contributor

Re: Laminating plywood for pergola rafters

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

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