Pergola Rafters


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Old 08-23-14, 07:27 AM
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Pergola Rafters

I'm having a Pergola built, it will be 26' x 26' with one side attached to the house and the other side on columns on the corners. I hired an engineer to calculate the loads/deflection and he actually wrote me a great spreadsheet in Excel that calculates deflection using Glulam beams and associated loads. If I keep the load on the supporting beams to 1600 pounds I can use 3 1/2" x 11 7/8" x 26', (or any beam with a MOI of 480 or higher) Glulam beams and keep the deflection under 0.5". Since the Pergola will be 12' high I don't think 1/2" of deflection will be noticable, he recommended that I keep the deflection under 1". I can obviously increase the 1600 load by increasing the MOI of the beams but Glulam starts getting pricey as it gets heavier. The Glulam is treated and rated for outdoor use.

My question is:
I need to find rafters, either 2" x 8" or 2" x 10" that will span 13 feet and be 15 feet in overall length with scroll work on one end. They will only have to support the weight of the small stringers and any snow load which will me minimal. I will need 24 of these rafters and I want them white. Since the Pergola is so high I want to keep it low maintenance. So I would need fiberglass, PVC, maybe hollow aluminum, any others? I would like them to simulate real wood as much as possible. I've searched google extensively for suppliers of just rafters but am not having much luck. Can anyone recommend the type of rafter to use, (material) and suppliers that sell it?

Thanks
Frank
 
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Old 08-23-14, 09:43 AM
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Pergola

Google "weather resistant pergola beams".
 
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Old 08-23-14, 12:59 PM
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Are you sure that you want to attach it to the house? What's wrong with free standing?
 
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Old 08-23-14, 06:18 PM
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Thank You
Nothing wrong with free standing. One post would interfere with a bay window that is in the kitchen. Is there a problem attaching it to the house? Actually, as designed now, it will lay on the roof of the house.
 
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Old 08-23-14, 08:07 PM
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A ledger board attached to the house can collect water & that can cause damage. I wouldn't risk it for a pergola.
 
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Old 08-24-14, 11:14 AM
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Do you have a drawing or sketch of what you are planning to build? I'm having a little time envisioning it since in your original post you said it was going to be 26 x 26 and you are talking about 15' rafters. Having the one and lay on the roof really sounds like a bad idea. Water is going to get trapped behind the beam that rests on the house. Again a drawing may help clarify this part of the design.
 
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Old 08-24-14, 03:22 PM
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My sketches are at work. The pergola is 26' feet wide post to post, it is in the shape of a "U" with an addiditonal beam down the middle sort of making it a box "3" look, the 3 beams will land on the roof of the house. They will be mitered to the pitch of the roof and set on the existing shingles, they are going to flash & tar where the beam lands on the roof. The beams are designed to land on the roof directly above the main support wall inside the house. Braces will be added between the main support wall up to the bottom of the roof joists which are stick built.

In order to span the 26' feet I was going to use 2 rafters 15' long placed end to end spanning a total of 30 feet, each rafter will stick over the beam 2 feet.
 
 

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