Pergola with reverse slope

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Old 09-28-15, 07:57 AM
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Pergola with reverse slope

Hi everyone. I'm looking for some feedback here. Last night I just finished building a pergola. It's 20 feet long by 14 feet deep, and one side is attached to our brick house (8 inch lag bolts through the brick veneer--attached to the frame of the house). I built the pergola with three 6 by 6 posts on the other end. The rafters are 2 by 10s. Pressure treated wood for everything. I dug 30 inch holes in the backyard and used 12-inch sonotubes for the footings--used Simpsontite post anchors.

Everything went smoothly and the pergola is solid. However, because of the construction of the house (mansard roof), I could only have a 100 inch ceiling height at the house. Consequently, I designed the pergola with a reverse slope, so that away from the house the ceiling gets taller--the other side of the pergola is 5 inches taller, so theres a reverse slope to the roof.

I thought it was a great idea when I came up with it, but looking at the finished pergola from the side, it looks a little goofy. You can't really tell from the other angles, though.

Obviously if this structure had a roof it would be a bad idea to have a slope toward the house for water runoff--but I figured the rain isn't going to channel down the pergola like a traditional roof, so I shouldn't have to worry about that.

Anyway, I was just wondering if anyone could think of potential problems with this design aside from the aestetics. Like I said, the pergola itself seems very solid. If you google Pergolas with reverse slope, you can see that other people have designed similar structures. I don't have a finished picture, but I've attached one from the early stages--you can kind of see the reverse slope from the pictureName:  pergola.jpg
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Last edited by gopujols; 09-28-15 at 09:50 AM.
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Old 09-28-15, 02:52 PM
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Welcome to the forums! It looks good, but I sit here questioning what could have possessed you to do such a thing. Water will run back on the tops of the wood to your house, so figure on that. 5" is a mile. If it were mine, I would lower the cross pieces to compensate for that 5" and trim off the pencils sticking up so high, unless you have another feature planned for them
 
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Old 09-28-15, 08:10 PM
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Thanks for the suggestions. I am not completely done with the pergola--I was going to cut off the pencils. You asked why I would do such a thing--to give myself more ceiling height. I could cut the notches in the rafters deeper, but theyre already at 4 inches deep now. I don't have 5 inches left to cut. Would it make a difference if I cut 2 more inches in the notch, lessening the slope by 2 inches?

As for water runoff, do you really think that much water will stay on the top of those boards to run toward the house? I forgot to mention I will also be putting a series of 2 by 4's perpindicular to the rafters screwed in on top of the rafters. Do you think that is enough to break the flow of water heading toward the house?
 

Last edited by gopujols; 09-28-15 at 08:35 PM.
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Old 09-29-15, 04:24 AM
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It isn't so much that will be running the full length, but water coming off your roof, hitting the top of the rafter and moving backwards. Did you silicone your ledger bolt holes? Did you flash over the ledger and onto the rafters?

My solution would be to unbolt the long exterior ledgers, re drill holes and re position the ledger 5" lower. I would not cut deeper throats on the rafters, either.
 
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Old 09-29-15, 06:29 AM
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No, I didn't silicone the bolt holes or flash the ledger. The ledger sits under the mansard roof and on a brick facade, so I didn't think it would get water. I do plan on cutting pieces of 2 by 10 to cover the joist hangers in between the joists--I could add flashing at that time. Or I could attach flashing at the end of the roof so it directs water off the roof and kicks it off the house.

The only problem I have with lowering the exterior beams 5-inches is that my joists might be too short then. I have barely enough wood to nail them in as they are now--tilted up a little. If I move them down they might end up being too short. I guess I can make my notches bigger to compensate for that though.

Do you think if the pergola is level I can get away with not flashing the ledger?
 
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Old 09-29-15, 06:55 AM
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Your joists will get longer if you lower them on the posts, not shorter. With it level you may have less of a chance of water intrusion.
 
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Old 09-29-15, 08:35 AM
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So with a brick house, would the purpose of the ledger flashing be just to protect the ledger from premature rot from water getting behind the board, since water can't penetrate the brick to rot anything out inside the house?

currently with my setup, the rafters (2 by 10) are shorter than my ledger (2 by 12), so theoretically water would travel down the rafter, hit the surface of the ledger, and trail down.

So at least from the top, water shouldn't be able to move to the back of the ledger board. I guess the water can climb up the ledger from the bottom, though, through capillary action--so maybe I should put flashing at the bottom of my ledger to direct the water off the wall? My ledger board is really tucked up under the house, so it will be hard to get flashing above the ledger board.

I am definitely going to level out the pergola, but without flashing in my situation, the risk is a prematurely failing ledger board correct? Thanks for helping me with this--I promise this is my last question
 
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