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Old 12-21-2017, 07:01 PM   #21
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Re: Dormer


I personally would triple the outer rafters too. I think the rule of double rafters is over used to a negative.
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Old 12-21-2017, 07:23 PM   #22
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Re: Dormer


The doubled up rafters will have to carry the load of the header and the header is now carrying the load of part of the original roof and at least half of the new gable dormer roof all transferred to two points on the exterior wall and to a lesser degree to the main ridge board and to the rafters on the opposite side of the ridge board. Plus, now the header is carrying a point load in its center from the gable ridge.
The connections for all of this have to be designed also. Seems a bit dicey to me.

Andy.
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Old 12-21-2017, 07:35 PM   #23
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Re: Dormer


Not arguing with you Andy, but I have a question.

I thought that roof loads are calculated by their horizontal spans. If that's true then there would be less load on the ridge, as some of the load is carried by the dormer ridge to the outside wall.

I do agree that there may be point load issues, but I do not possess the brain power to address them.
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Old 12-21-2017, 07:38 PM   #24
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Re: Dormer


If I am trying to size lumber for something like this and an architect isn't involved I call my lumberyards supplier. They will run the numbers for the exact lumber I will be using and tell me sizes and how many to carry the load. They even give me a print out for the building department. That would be a great option if your lumber yards supplier has such a service.
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Old 12-21-2017, 08:38 PM   #25
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Re: Dormer


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Originally Posted by B.Johnson View Post
Not arguing with you Andy, but I have a question.

I thought that roof loads are calculated by their horizontal spans. If that's true then there would be less load on the ridge, as some of the load is carried by the dormer ridge to the outside wall.

I do agree that there may be point load issues, but I do not possess the brain power to address them.

And this is one reason why you should have an engineer walk you through this.

Edit - sorry B Johnson, I was in a hurry and thought this was from the OP...

Last edited by hdavis; 12-21-2017 at 09:03 PM.
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Old 12-21-2017, 08:57 PM   #26
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Re: Dormer


If you are using LVL's for rafters your plans will require a stamp. Bring your prints to a SE and have them stamp or mod the plan.

Last edited by JAH; 12-21-2017 at 09:01 PM.
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Old 12-21-2017, 09:08 PM   #27
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Re: Dormer


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And this is one reason why you should have an engineer walk you through this.

Edit - sorry B Johnson, I was in a hurry and thought this was from the OP...
No problem, I never want to stop learning.
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Old 12-21-2017, 10:09 PM   #28
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Re: Dormer


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I'm not an engineer....

I say as long as your doubles are strong enough to carry the load you should be fine. Personally I would triple them. Obviously your floor is going to keep the rafters from spreading and if it can't spread it can't come down. You will also need to support the dormer ridge at the gable wall. If you want to post a link to your .plan file I'll see if I can fix the overhang in front of the dormer for you. I'm certainly no expert, but you might need to change the wall type directly below the dormer to high shed wall type or you should be able to edit that section of the roof directly.
Thank you, that's my thinking as well, but I've sent an email to the engineer regardless. Hopefully, he's not on vacation yet.

Not sure how to post a link to the .plan file?
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Old 12-21-2017, 10:12 PM   #29
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Re: Dormer


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If I am trying to size lumber for something like this and an architect isn't involved I call my lumberyards supplier. They will run the numbers for the exact lumber I will be using and tell me sizes and how many to carry the load. They even give me a print out for the building department. That would be a great option if your lumber yards supplier has such a service.
That's a great idea. I'll check with them. I use National Lumber in Newton.
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Old 12-21-2017, 10:34 PM   #30
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Re: Dormer


It's also possible to have custom trusses made to HANDLE this, depending on whether they would interfere with your celing plans. The truss company does the engineering.
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Old 12-22-2017, 12:07 AM   #31
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Re: Dormer


Since it is a Timber Frame building, you might want to find an Engineer familiar with TF structures.

HERE is the website address for the Timber Framers Guild. There are a ton of them in the NE part of the country, many with in-house Engineering services.

They will be more familiar with designing connections and routing Load Paths, etc through the frame than a typical SE, IMHO.
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Old 01-07-2018, 08:45 AM   #32
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Re: Dormer


Plan looks good to me, I've done that style dormer with the same framing details with no problems...

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