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Old 06-25-2018, 06:09 PM   #1
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Looking for ideas for building attachment that allows vertical movement.


I'm working on a plan for a patio cover. This will be a self-supporting 4-post design. I have attached a pic of a similar structure, the difference is that my design will not have the diagonal braces that you see in the pic. Instead, I will attach it to the side of the house for lateral support. The attachment will not carry any vertical (gravity) load since I don't know the capacity of the footings of the house. The attachment will be along the side with the joist ends (the side that is mostly facing you in the pic). Since the roof deck will provide a rigid diaphragm, if I attach it to the house this way I won't need any bracing.

BTW, our city requires that this be attached if it's within 10 feet of the house anyway, so I'm killing two birds with one stone - 1) satisfying the city requirement and 2) stabilizing the structure laterally.

Now, here's the problem, and the question. Since this will be build with local green Ponderosa Pine, there will be considerable shrinkage. I expect the roof height to be lower by 1/2 to 1 inch when it's done shrinking. So, to allow for the shrinkage and also avoid loading the house, the attachment will need to allow for some vertical movement. I'm thinking of some sort of slotted bracket, but I haven't seen anything like that and I am looking for ideas for this connection. Oh, and appearance matters.

Got any ideas?
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Old 06-25-2018, 06:34 PM   #2
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Re: Looking for ideas for building attachment that allows vertical movement.


I have no clue what your local conditions are but is are no snow loads and the wind never blows?
Why Green lumber?
The only way I would build something like this is if it was tied into the roof, not at the soffit or rafter tails and add diagonals to keep it from swaying on the other end.
Every DIY roof done like you suggest leaked and swayed.
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Last edited by joecaption; 06-25-2018 at 06:36 PM.
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Old 06-25-2018, 06:36 PM   #3
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Re: Looking for ideas for building attachment that allows vertical movement.


You will be putting a ledger with flashing against the house?
You could put adjustable legs under the posts and dress the bottom of the post when dry.
Or heavy steel angles on each side of the joist with slotted holes or bolt thru with a slotted hole in the joist.
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Old 06-25-2018, 06:53 PM   #4
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Re: Looking for ideas for building attachment that allows vertical movement.


Quote:
Originally Posted by joecaption View Post
I have no clue what your local conditions are but is are no snow loads and the wind never blows?
Why Green lumber?
The only way I would build something like this is if it was tied into the roof, not at the soffit or rafter tails and add diagonals to keep it from swaying on the other end.
Every DIY roof done like you suggest leaked and swayed.
Design parameters (already been accounted for in the design):
10 psf dead load, 20 psf live load (snow)
90 mph

Green Ponderosa ("season in place") for this type of style is the norm around here. I could use DF, but I wood still have to allow for shrinkage.

I would not attach to a soffit or rafter tails. I have a good attachment area on a corner of the house and a porch header, which I believe will handle any horizontal load due to wind. Tthe footings may not be sufficient for the gravity load, therefore the self-supporting design (as suggested by my "friends" at the city permit office.

This is the most common (and very popular) style here, though often it's just a 2-post, single beam design using a ledger to transfer ~1/2 the load to the house. There are no diagonals used on the outer beam with this design. I'm just adding the inner posts and beam, and I'll still attach it, though there will be no gravity load carried by the attachment.

Some will bury the posts 3ft in the ground, but the city won't permit it and the posts will eventually rot (even here in the high desert).

I do have the option of standing it away from the house a few inches (so no flashing required), though I still have to use a good attachment to stabilize it. The city guys suggested some sort of "lattice" with diagonals.
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Old 06-25-2018, 07:16 PM   #5
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Re: Looking for ideas for building attachment that allows vertical movement.


Quote:
Originally Posted by Nealtw View Post
You will be putting a ledger with flashing against the house?
I plan to use a ledger but not for gravity load, only horizontal load. Probably a 2x8 or maybe 3x8 (rough). If I attach the top deck directly to the house, I will have to flash it. If I don't attach it, there will be a little space where the rain falls between the existing house porch roof and the new cover. Still thinking about that, though it obviously changes the requirements for the structure attachment to the house.

Quote:
Originally Posted by Nealtw View Post
You could put adjustable legs under the posts and dress the bottom of the post when dry.
Not a bad idea. I'll think about that.

Quote:
Originally Posted by Nealtw View Post
Or heavy steel angles on each side of the joist with slotted holes or bolt thru with a slotted hole in the joist.
Funny you should suggest that. It's one of the ideas I had. I also considered cutting a kerf into the end of each of the 8 4x6 joists and using a piece of angle with a slotted hole for the bolt through the joist. That way the slotted angle is hidden. Simpson has a concealed joist tie that works kinda like that (the CJTZ), though it is designed to carry a gravity load so of course isn't slotted and uses multiple dowels.

BTW, the city guys told me the connector I use doesn't have to be rated. They suggested the Simpson A24 but with that the bolt would be about 2" from the end of the joist and I'm not comfortable with that. I'm thinking 3"x4" or 3"x5" steel angle to move the bolt back a little (the slot would be in the long leg of the angle). If I use the angle-in-kerf method I'd want to cut the short leg off to maybe 2" so it's not so conspicuous. They said 2 connections is enough if I have a rigid diaphragm roof, but I'd just do all 8 for maximum strength.
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Old 06-25-2018, 07:36 PM   #6
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Re: Looking for ideas for building attachment that allows vertical movement.


While you probably don't have to worry about a frost line, you still might want to consider footings even if they are only 2 feet deep. There are none in the sample pic. Are footings in your plans?
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Old 06-25-2018, 07:44 PM   #7
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Re: Looking for ideas for building attachment that allows vertical movement.


Quote:
Originally Posted by Guap0_ View Post
While you probably don't have to worry about a frost line, you still might want to consider footings even if they are only 2 feet deep. There are none in the sample pic. Are footings in your plans?
Yes, thanks. The permit requires 16" but I'll probably go 24".

I think the sample pic has them, and they used some kind of heavy steel post bases to reduce the amount of bracing required (at least in one direction). Looks like they still needed diagonals in one direction, though it's not obvious why they didn't need them at all in the other direction. I know this builder's work and it's pretty good, but I don't think I'd trust a steel post base to resist rotation, without additional top support.
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Old 06-25-2018, 08:03 PM   #8
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Re: Looking for ideas for building attachment that allows vertical movement.


I think that 24" is a good idea.
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Old 06-25-2018, 08:56 PM   #9
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Re: Looking for ideas for building attachment that allows vertical movement.


the ledger would have to be attached just as serious as normal for lateral loads.
If you have it attached to the house the roof sheeting will stop any twisting action just like any flat deck we build. I hope you are ordering No Heart Wood timbers
I like the adjustable post holder because they also look after some settling of piers and footings And the can be made to high specs like 4 bolts deep anchor in concrete and single 3" steel post as long as you want.
We did post connection like this but we hid the bolts in countersink and plugs.
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