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Author Topic: Timber Frame Lean To Question  (Read 497 times)

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Offline Jrsmith1406

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Timber Frame Lean To Question
« on: November 14, 2019, 12:25:21 PM »
Hello all,

Im new to the forum and seeking help for a lean to structure. The planned lean to is 32 wide and 14 deep from post to attached building wall. The plan is to have (5) 8x8 posts with (2) 8x8x16 beams on top. The rafters is where I have questions. Im thinking either 4x8x16 or 6x8x16 and planned to space them 3-4 apart for a total of 8-10 rafters. The decking will be 2x6 TG so spanning 3-4 with that should not be a problem as I have a separate structure with timber trusses spaced 5 apart. Does anyone know if I should use the 4x8x16 rafters or 6x8x16 rafters. Additionally this will be on a 6/12 pitch. Thanks. 

Offline Brad_bb

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Re: Timber Frame Lean To Question
« Reply #1 on: November 14, 2019, 01:16:48 PM »
Please put your location in your profile.  It will then show up in your posts.  That way we know where you are and whether you have significant snow load (in Minnesota) or none (in Alabama).  Will it be in a location with a lot wind load?

You're talking about timber sizes but what species?  Also, there's a big difference between 3' and 4' spacing.  I'd rather see you go closer and have a stiffer roof than too far apart that will only save you 3 sticks or so.

I notice you said 5 posts for 32'.  That's a post every 8 feet.  You could probably increase that.  Do you need them that close together?
Anything someone can design, I can sure figure out how to fix!
If I say it\\\\\\\'s going to take so long, multiply that by at least 3!

Offline Jrsmith1406

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Re: Timber Frame Lean To Question
« Reply #2 on: November 14, 2019, 02:41:30 PM »
Please put your location in your profile.  It will then show up in your posts.  That way we know where you are and whether you have significant snow load (in Minnesota) or none (in Alabama).  Will it be in a location with a lot wind load?

You're talking about timber sizes but what species?  Also, there's a big difference between 3' and 4' spacing.  I'd rather see you go closer and have a stiffer roof than too far apart that will only save you 3 sticks or so.

I notice you said 5 posts for 32'.  That's a post every 8 feet.  You could probably increase that.  Do you need them that close together?
Thanks for the reply.  Location added. I live in Lincolnton, NC.  As for snow we may get 4-6" if that once or twice a year but that seems to melt quite quickly.  The structure will face west so I don't believe wind will be much of a factor as most of our heavy wind comes out of different directions in my experience at this property.  
As far as the timber, I will be using rough cut pine timbers.
In regards to the 5 posts, when I started this project I was not planning to use such a large beam to span the 32'.  I was simply going to use 6x6 posts and notch in a 2x8 band however my wife insisted I make it match the grilling patio connected to the south side of the garage  :o and I had already poured the footers for the posts.  Rather than tear those out and restart i'll just leave it be.  The 8' spaces will still allow me room to back my tractor implements in between the posts.

Offline ljohnsaw

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Re: Timber Frame Lean To Question
« Reply #3 on: November 14, 2019, 03:20:16 PM »
4x8x16 rafters or 6x8x16 rafters
 
You'd get more bang for your buck going to 4x10 rafters than 6x8.  The height of the "beam" is what gives the stiffness rather than the width.  Even going from a 4x8 to a 3x10 is going to be a better rafter.
John Sawicky

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SkyTrak 9038, Davis Little Monster backhoe, Case 16+4 Trencher, Home Built 42" capacity/32" cut Bandmill up to 54' long - using it all to build a timber frame cabin.

Offline Jrsmith1406

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Re: Timber Frame Lean To Question
« Reply #4 on: November 14, 2019, 03:38:58 PM »
4x8x16 rafters or 6x8x16 rafters

You'd get more bang for your buck going to 4x10 rafters than 6x8.  The height of the "beam" is what gives the stiffness rather than the width.  Even going from a 4x8 to a 3x10 is going to be a better rafter.
I used 6x8s to build the trusses on my grilling patio so my wife not really worried about the structural integrity prefers the chunkier look however I do understand what you're saying.  I may try to get her to move to a 4x10 if that works better.  This "simple lean to" has gone from simple dimensional lumber to a masterpiece to house my trailer and tractor implements.....I think this space may get hijacked  :-\

Offline Don P

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Re: Timber Frame Lean To Question
« Reply #5 on: November 14, 2019, 07:21:52 PM »
Lincolnton is I think just in the 15psf snow design belt, the 10psf belt cuts in below you I believe, I've got family in Shelby. Either way wind code minimum of 20psf would control. So call it 20 psf live load + 10 psf dead load= 30 psf total load

Figure load per rafter;
Rafter span uses the horizontal measurement so 14' span x 4' spacing=56 square feet bearing on each rafter.
56 square feet x 30 lbs per square foot =1680 lbs uniformly distributed load/rafter.
Go here to try 4x material;
http://forestryforum.com/members/donp/ddsimplebeam.html
load 1680, span 168, width 4, depth 8, SYP #2@8", wind duration, Repetitive member NO (that is for spacings 2' or less apart), size 4x8, no, no, click "show result", congratulations!

Go here to try 6x material (heavy timber) Don't forget this folks, design values change at 5x5 and larger, notice the adjusted differences between them.
http://forestryforum.com/members/donp/beamclc06b.htm
Entries are the same, dead load is 560, congratulations!

Compare the deflection between the two, the 6x8 has about half the deflection under FULL load compared to the 4x8 but either passes.

Your 2x6 spanning 4', we can clear that up another way, check building code;



#2 SYP, you're actually good out to 6' spacing.
Hope that all made sense, holler back if something didn't.

I just spent the last couple of days reading a book by Sharyn McCrumb, "Kings Mountain", a good one for winter nights by the fire.
A laborer works with his hands
A craftsman uses his brain and his hands
An artist uses his brain, his hands, and his heart

Offline Jrsmith1406

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Re: Timber Frame Lean To Question
« Reply #6 on: November 15, 2019, 10:08:11 AM »
Lincolnton is I think just in the 15psf snow design belt, the 10psf belt cuts in below you I believe, I've got family in Shelby. Either way wind code minimum of 20psf would control. So call it 20 psf live load + 10 psf dead load= 30 psf total load

Figure load per rafter;
Rafter span uses the horizontal measurement so 14' span x 4' spacing=56 square feet bearing on each rafter.
56 square feet x 30 lbs per square foot =1680 lbs uniformly distributed load/rafter.
Go here to try 4x material;
http://forestryforum.com/members/donp/ddsimplebeam.html
load 1680, span 168, width 4, depth 8, SYP #2@8", wind duration, Repetitive member NO (that is for spacings 2' or less apart), size 4x8, no, no, click "show result", congratulations!

Go here to try 6x material (heavy timber) Don't forget this folks, design values change at 5x5 and larger, notice the adjusted differences between them.
http://forestryforum.com/members/donp/beamclc06b.htm
Entries are the same, dead load is 560, congratulations!

Compare the deflection between the two, the 6x8 has about half the deflection under FULL load compared to the 4x8 but either passes.

Your 2x6 spanning 4', we can clear that up another way, check building code;

(Image hidden from quote, click to view.)

#2 SYP, you're actually good out to 6' spacing.
Hope that all made sense, holler back if something didn't.

I just spent the last couple of days reading a book by Sharyn McCrumb, "Kings Mountain", a good one for winter nights by the fire.
Incredibly helpful information.  Thank you for that.

Offline Jrsmith1406

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Re: Timber Frame Lean To Question
« Reply #7 on: November 15, 2019, 10:24:00 AM »
Thanks to everyone for the input.  With all of that cleared up, what would you guys recommend as the best way to connect this to the garage wall?  Simply throwing up a ledger board and toe nailing these beams into place just doesn't seem like the way to go.  Any recommendations on size of ledger?  Attachment of ledger to garage wall?  Attachment of beams to ledger?  Thanks.

Offline Don P

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Re: Timber Frame Lean To Question
« Reply #8 on: November 15, 2019, 05:03:54 PM »
What is the construction of the garage? Siding? Is there a footing outside it that you can get posts down on?
A laborer works with his hands
A craftsman uses his brain and his hands
An artist uses his brain, his hands, and his heart

Offline Jrsmith1406

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Re: Timber Frame Lean To Question
« Reply #9 on: November 15, 2019, 05:42:07 PM »
What is the construction of the garage? Siding? Is there a footing outside it that you can get posts down on?
The exterior wall that I'm trying to attach to is a 2x6 stud wall with 7/16" sheathing and Hardie siding.  Unfortunately the garage footer is mostly consumed by the cement block and brick

Offline Don P

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Re: Timber Frame Lean To Question
« Reply #10 on: November 15, 2019, 07:56:26 PM »
I'd remove the hardie in the ledger area and flash back over the finished roof.

You have 840 lbs at the top end of each rafter, 6720 lbs total that the ledger is supporting.

The Engineering Services Report for LedgerLoks, available at Lowes is here, look at table 4 far right column;
https://www.fastenmaster.com/?file=tl_files/fastenmaster2015/documents/files/ESR-1078.pdf

6720lbs/260lbs per fastener=26 @5" ledgerloks minimum. I'd still prefer posts on footings but that would support a ledger. You can rest on the top of a beveled ledger if you have access to the inside of the wall, can secure blocking and run lags or timberloks thru the blocking into the ends of the rafters. Otherwise you could use something like a Simpson concealed joist tie (CJT3);
strongtie.com

They also have "strongdrive screws" that may have higher shear capacity for the ledger.

If this doesn't need to be inspected I've welded hangers for sawmilled beams using angle and bar stock. I'd incorporate a top flange on these to hook over the ledger and turn the "ears" in to tuck in behind the rafters, screwing those inturned ears into the ledger. If you can fabricate it you can get the width and slope right. Look at their concealed hangers for basic ideas, something like an "HUCTF" with a sloped bottom.

I've been shingling on an 8/12 roof all day, I've done my Achilles stretches for awhile :D
A laborer works with his hands
A craftsman uses his brain and his hands
An artist uses his brain, his hands, and his heart


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