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Timber frame solar carport  RSS feed

 
Bill Bradbury
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Location: Richmond, Utah
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I have been contracted to design and build a carport/solar charging station for a client here in northern Utah. Aspect is due south and clear and there are already piers in the asphalt slab from the old carport. I'm looking for design critique on these rough sketches right now and will post photos later as the build progresses.
SolarCarport.jpg
[Thumbnail for SolarCarport.jpg]
Front view
SolarCarportSideview.jpg
[Thumbnail for SolarCarportSideview.jpg]
West side
 
Jay C. White Cloud
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Very exciting Bill...wish I could come an play with you on this!

Without footprint size of width and length, I don't yet have a good understanding of potential loads. I love the use of horizontal bracing modalities. I would note that for ease of building (presuming I haven't misread the current plan) that it may warrant having the gable "bent beam" that are the 2x4 become a "pass through" member in the outer post, instead of "deadheaded" into the mortise. This also greatly strengthens this type of joint...especially if "toggle locked" from within the mortise, and/or becoming locked into the corresponding 2x6 "connecting girt." If you do chose to go with the "blind mortise (another name for "deadhead") then I suggest "dovetailing" the mortise to lock the joint when it is wedged from the top. In its current rendition I think I would separate the bent girts and the connecting girts and not have them enter the 6x6 at such close proximity.

Because of the diminutive size I see in all the members I am understanding this not to be a very large structure?

I am not tracking well the 4x8 on flat "rafter plate" and the 2x6 joist and how the are jointed to one another?

If you can get lumber from to your specifications from a local sawyer, then there are additional modifications to this design I would suggest that follows a more traditional sizing and layout of the structural members...

I really look forward to additional information!! Great Project to work on...

j
 
Bill Bradbury
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Location: Richmond, Utah
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Thanks for the help Jay,

That 2x6 is a girt and on flat as well as the 4x8 which it dovetails into, but drawn wrong, good catch. I will lower the bent girts to keep the joints separated at the posts.

The footprint is not quite 12x24'; any advice on sizing would be appreciated and yes the sawyer will cut whatever I order.

I could go with pass through if that is better, but I was planning on a wedged and dovetailed blind mortise and tenon.

Thanks for the help, I know the structure will be much stronger and more elegant with your seasoned advice.

All Blessings,
Bill
 
Jay C. White Cloud
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Hey Bill,

I started a little Sketchup CAD model for this project. If you give me a wee bit of time (and more info) I will get a model that a frame can be cut from. A great project to document here for folks to follow along with...

That 2x6 is a girt and on flat as well as the 4x8 which it dovetails into, but drawn wrong, good catch. I will lower the bent girts to keep the joints separated at the posts.


Hmmm...o.k.

I can work with the 4x8 on flat as the load is transferred to the 2x6 on edge (this needs to be bumped up to a 2x8 if possible.) The 2x6 joists on flat doesn't work even with light loads if spanning 12'. The mentioned "dovetail" drop in joint (not really a good joint in general for most applications) brings us to the rule of thumb:

"two's and three's...three's and four's"

Two's and Three's

This little diddy of a suggested rule is directed at the top of receiving members (i.e. summer beams, connecting or bent girts, etc) and how much extra space must (should) be left either from the outer edge of the member to the joist housing or to the edge of the opposite side where there is a mirror housing for another joist, as is often found in "summer beam" layouts. So...in your case if we did employ a "dovetail" lapping joint to secure the joists, there should really be 3" of material left in the 4x8 on flat after the housing mortise is cut.

Three's and Four's

This is a general old "rule of thumb" about joist and there carrying member receivers.

When a joist (i.e. its mortise of whatever type from "dovetail" to "laps") is "let into" its carrying member there must be (or should be in most cases) at least 3" to 4" of material left in the carrying member from the bottom of the joist housing (i.e. mortise)...or better yet...the joist housing should never go past the "neutral axis" of the receiving member. To break this rule involves some pretty heady engineering, and/or deep knowledge of the wood species selected and its different load dynamic characteristics.

Dovetailed joints are plagued with issues...Primarily with "withdrawing" and with weakening the receiving member because of fiber destruction occurring on the top of the receiving member. Now since the top of a receiving member is in compression, this isn't a hideous crime but it does weaken substantially the timber. This is the reason "tusk" and "soffit" tenon connections (though difficult to facilitate in raising) are the strongest connecting joint for joist to receiving member, as the mortise housing enters into the "neutral axis" of the loaded timber. The other disturbing challenge with "dovetailed joints" is the weakening of the joist by the "shear effect" it has on this member. Here is were another old rule of thumb comes up:

"Less is More"

When lapping a joist, purlin or other loading member...never allow the member to have an unsupported 90 degree lapping. The member that has a "lapping tenon" (e.g. dovetailing in this case) must be reduced at an angle of at least 40 degrees from the bottom of the tenon to the bottom edge of the member. Sharp 90 degree angles concentrate "shear presures" at a location in the joint that can (will?) cause the member to split at that point with the ensuing crack that can radiate the length of the timber. Below illustration presents a 6x6 next to a 2x6 on flat as it would look in the current rendition of your model.

I also have questions about the 12'x24' layout?? Does the gable run along the 24' length? How many and what are the post spacings. With this infor I can generate a more accurate CAD model to discuss.



Look forward to more info...

Regards,

j
 
Bill Bradbury
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Location: Richmond, Utah
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Hello Jay,

The carport is just under 12x24 with 6 posts all around 11'7" from each other. The roof is just a shed style, all south facing, with a pitch of 6 or 7 on 12.

I would love to get a sketchup file to work with! I'm not much of a computer guy, but I really want to learn this program.

Feel free to enhance my design in any way you think is necessary.

The 2x6 joists will be on edge in (dare I say it) metal joist hangers, but at 12' should still be 2x8's on 16" centers and the floor of the loft will be 3/4" CDX.

I know I already said it twice, but thanks for your help. Your deep knowledge of these traditional framing systems and willingness to share openly is a rarity and very much appreciated.

All Blessings,
Bill
 
Jay C. White Cloud
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Hey Bill,

O.k got it...shed roof...

Err..Uhmmm...I think this is why I was so confused to begin with, and perhaps why I thought you had draw only half a gable end?? A 6/12 pitch roof slope yields the Arctangent of .5 or 26.565°

That would make the front posts (if the back posts are 8') over nineteen feet tall!!

That is one heck of a "wind catcher," so please advice and I will keep going with the CAD model for you... I am fine with this (though unusual and a bit awkward in affect and appearance) yet is this a pitch that is set because of the solar array collection being mounted on it? Also, has your friend looked at self tracking turreting systems yet? They are far more efficient and superior to fixed array assemblies.

Waiting for you before proceeding...

Regards,

j
 
Bill Bradbury
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Location: Richmond, Utah
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Hi Jay,

Yep, that's what the client wants. There is not a lot of room, since he has a garage and a rental cottage in his backyard and the carport will be sandwiched between the 2.

I've been thinking about a ridge on the back side with an eyebrow roof to minimize wind catching the northern eaves.

The client emailed some photos, I will send them to you.

All Blessings,
Bill
 
Jay C. White Cloud
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Hey Bill,

This is far from complete, but is a good foundational design within the parameters requested...

I will send you an email with a file attached with the "Draft 1" version. This is a 6/12 pitch as the 7/12 generated post that are way too tall...



Regards,

j
 
Bill Bradbury
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Thanks for the help Jay,

I got your file in my email, but this one doesn't seem to work.

The local saw mill, where we will get the wood for this project does not age the logs for very long, so the wood is very wet and green. I typically get a lot of checking when I air dry in our dry climate. I usually stack the boards log cabin style and don't cover them. How do you suggest to dry the boards so they don't check as much? What moisture readings do you look for before building?

All Blessings,
Bill
 
Jay C. White Cloud
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Sorry folks that the other screen shot of this project failed... I would go back and repair it if I could.

Above is the current rendition of Bill's project I am helping with...The roof deck and rafter are removed for clarity and the colors are part of the CAD layering system to keep track of where I am working...

Hello Bill,

I sent new files this morning I hope they open for you.

The local saw mill, where we will get the wood for this project does not age the logs for very long, so the wood is very wet and green.


No one can actually really "age" a log per se. In some (very limited) Buddhist Temple work the logs will be "cured" for up to 100 years, (some wood is even "water cured") but this doesn't even make a dent in truly drying them, nor do we want that in most applications.

Timber framing and even most of my furniture work is don in the "green" (aka wet) condition of the wood fresh off the mill. I even lay floors with material that hasn't been out of a tree more than a week to a month. It is al about the "way" and "how"...not the "what."

I typically get a lot of checking when I air dry in our dry climate. I usually stack the boards log cabin style and don't cover them. How do you suggest to dry the boards so they don't check as much? What moisture readings do you look for before building?


Only for very limited applications (i.e. some super refine furniture forms, etc) do I use dried wood...

To dry wood well, when it is needed, I dry it as slowly as possible. In your area, and with the species available to you, the boards do probably dry entirely to fast, and even get a form of "flash over" or "case hardening" from the type of climate there.

First (this probably isn't happening as most modern sawyers don't have the knowledge of wood that our forbears did) the tree after they are cut into bolts should be "end seal" and have a sprinkler house running over them whenever it is sunny and/or hot. You will find this in the better "saw yards" that take care of there wood before milling. Huge lots with stacks of logs and giant lawn sprinklers ever 100 feet or so running water over them. Many even recycle this water if they can, while others will store the logs in ponds to "cure" them and keep them from drying out before milling.

At minimum you will need to "wax" or "end seal" the boards as soon as you get them and try to get some type of shading over the location that you stack them...It may be necessary to "cleat" the end of the boards if there is evidence of "reaction grain" in the wood. This is assuming that you care to dry them at all. We don't in most cases for the work we do, especially in projects like this Carport. There is simply no need for it, as fresh off the mill will be fine and trying to "joint" dried would is entirely too difficult even in Conifer species.

The "art" is learning to read the wood and how it contracts (and expands) seasonally and which ways to orient the wood or the board/timber in the wood so the grain works for you, and not against. For example, most "professional" (??) floor companies charging top dollar hire installers that can't or don't bother "orienting" the floor boards so they are only "bark side up." This is an old rule of thumb..."use the wood as it falls in the forest or grows in the earth...to do otherwise is evil and brings Demons to the work..." If we can't get wood from a sawyer to our mill spec standards than we have to "read the wood" we get and use it accordingly. As you get into this project we will get into things like "pith side" and "bark side" orientation, crown and root reading of a timber and how it should be oriented in the frame etc.

Regards,

j

I will try to update this if someone makes a mistake and damages or erases the file. Here is a public copy accesses to this project to play with and learn from.

https://drive.google.com/file/d/0B1BtPD-BzGILNXJVMnRTVnlXc3M/view?usp=sharing

 
Mauro Pacitto
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Location: Toronto, Ontario
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Hello,

Hello everyone and thanks.


I am new to permies.com. It is a fantastic resource. I am particularly interested in learning about natural building. I am floored by the incredible knowledge being freely shared. I am mostly watching and learning but will contribute if and when I can. I also do drawings and may be able to help out with some projects, time permiiting.

Thanks

Mauro
 
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