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Author Topic: First Timber Frame Build  (Read 1446 times)

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Offline aguaman99

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First Timber Frame Build
« on: January 28, 2019, 07:40:51 PM »
hey guys I'm a new member but have been reading a ton of everyone's posts for several weeks now. Definitely some knowledgeable folks in the group! I started reading and quickly became obsessed  when I began designing my first timber frame project :P.... I've been in the construction industry for 30 yrs, so I have building and tool knowledge from those years of experience. This is something new and somewhat outside my skill set.  Currently I have separate small wood and metal shops that need to be combined into one single larger shop. I've decided on a 38 x 56 timber framed structure and am in the preliminary stages of design. Prior to engaging with the structural engineer I wanted to post the design here in its current state and get your feedback. I figure i can then take that advice, tweak things, finish the design. Once i get the general design right I'll start to work out the joinery and other architectural details and then sit down with a structural engineer to get serious.

I'm most curious about my post and beam size selections. Its a fairly simple rectangular build. My largest span is only 17'. For cost reasons I'm trying to work with white pine and keep the majority of the members to 6x6's. The king post truss I've come up with for the 17' span utilizes 6x10 rafters and tie beam with a 6x12 king post and 6x8 braces.... I designed it this way from reading your posts, research and then mostly my gut.....  anyway I've attached a link to the drawings and am anxiously waiting for you guys to tell me I'm crazy :D

In short... what do you all think of the 6x design strategy?


preliminary drawings

Offline Don P

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Re: First Timber Frame Build
« Reply #1 on: January 28, 2019, 09:19:01 PM »
Hi aguaman99,
First, stick your drawings on the forum server so they stay with this thread, click "modify" on your original post then at the bottom of the frame click on "attach documents and other options".

Do you have a side view? I can't tell what the unbraced column length is out of plane.

I don't understand the purlins with 1x4's let in up and down the roof, what is the rest of the roof going to be/ what are you supporting with those? I doubt you'll want to drop in notch the purlins into the rafters, I'd probably run them above or use some type of hanger.
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Offline aguaman99

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Re: First Timber Frame Build
« Reply #2 on: January 28, 2019, 10:10:41 PM »
well i thought id just go attach them as you suggested but its not very intuitive and i have no idea how to do what you suggested.... i can get to modify but then it doesn't seem to want to let me attach anything.... what am i missing?

Offline Don P

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Re: First Timber Frame Build
« Reply #3 on: January 28, 2019, 10:57:03 PM »
You got em, I just opened all 3 :)
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Offline aguaman99

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Re: First Timber Frame Build
« Reply #4 on: January 28, 2019, 11:06:45 PM »
yes  i did! thanks for your help.

now you should be able to see the bracing details and column heights. roof will be corrugated metal over foam and osb. complicated detail i haven't inserted yet however its well under the 15 lbs I'm designing to. 

regarding the rafter/purlins; i do intend to notch the purlins to the rafters via a dovetail. the 1x4 are just nailers for the additional roof layers. i was going to let them into the top of the purlins but have recently realized i should just nail directly over rafters and purlins so the top of the rafters and purlins will remain in alignment. i assume that is the glitch you were referring to.

Offline Racerx94

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Re: First Timber Frame Build
« Reply #5 on: January 29, 2019, 06:19:55 AM »
I am new to this forum also. Your drawings do not show any overhang on the ends or eves on the sides, are you planning on any?

Offline Don P

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Re: First Timber Frame Build
« Reply #6 on: January 29, 2019, 07:47:44 AM »
Actually the glitch with notching the purlins into the rafters is a little tougher. When Dick Schmidt did full sized testing of timbers what he found was the dimension to design around is the thickness between the notches by the depth. So if you have a 1-1/2" deep dovetail mortise coming in from each side of a 5-1/4" thick timber the effective rafter size is 2-1/4" x 10 at 8' centers rather than 6x10, probably a no go. That is why I was saying I'd probably run the purlins on top of the rafters or use some type of hanger if you want them down flush.

What I was wanting from the side view is whether there is something supporting the posts at around 9' above the floor in the 56' length, in other words I'm looking for the maximum unbraced length of the column in both directions.
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Offline aguaman99

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Re: First Timber Frame Build
« Reply #7 on: January 29, 2019, 10:52:42 PM »
Yes thats correct the exterior will have a built up foam and corrugated roof. The eves will be added on top of that insulating material

Offline aguaman99

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Re: First Timber Frame Build
« Reply #8 on: January 29, 2019, 11:22:17 PM »
Actually the glitch with notching the purlins into the rafters is a little tougher. When Dick Schmidt did full sized testing of timbers what he found was the dimension to design around is the thickness between the notches by the depth. So if you have a 1-1/2" deep dovetail mortise coming in from each side of a 5-1/4" thick timber the effective rafter size is 2-1/4" x 10 at 8' centers rather than 6x10, probably a no go. That is why I was saying I'd probably run the purlins on top of the rafters or use some type of hanger if you want them down flush.

What I was wanting from the side view is whether there is something supporting the posts at around 9' above the floor in the 56' length, in other words I'm looking for the maximum unbraced length of the column in both directions.
Thank you for your comments, this is the the kind of insightful feed back i was hoping to get ;-).   It did occur to me that some of my joints would be difficult with the 6x material for instance at the corner posts etc... I hadn't thought about the purlin notches affecting the integrity of the smaller timber but that makes perfect sense now that you pointed it out ;-) In your opinion would 6x be doable assuming I lay the purlins over the rafter in lieu of notching as you have suggested?
I had intended to brace in both x and y directions at the perimeter posts but nothing in the direction your concerned with has been considered at the taller interior columns yet.... if needed, one thought would be to introduce cross bracing from column to column in that direction starting just above the ceiling of the lower sections of the structure and that would start at the 9' elevation. Do you think i would need this between all the bents or could i just do one creating a single moment frame on each side of the structure, say in the middle 1 or 2 bays? One thing that is not yet shown in the drawing that could help with this (help hide them anyway)  is that there will be a second level that will be 16' wide between the taller columns joining the last three bents together. in this part of the design i could easily introduce bracing. The question there would be; does the moment frame need to be in the mid section of the structure or could it be at one end as I've described? hope that makes sense, let me know if its easier if i sketch something.

Offline aguaman99

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Re: First Timber Frame Build
« Reply #9 on: January 30, 2019, 12:49:08 AM »
here is a quick longitudinal section that shows my initial thoughts for bracing and also a rough idea of the interior framing that would capture the second level area. Just to give you an idea of what i had in mind so don't pay too much attention to my framing layouts or details please ;-)

Online Brad_bb

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Re: First Timber Frame Build
« Reply #10 on: January 30, 2019, 07:11:01 PM »
I'm confused about the roof.  Are there rafters?  If so what are they?  You can't just span 4' with a 1x4 laying on it's face.  Also, where are you located?  You can put your location in your profile and it will show up in your posts.  If I were you I would plan an insulated roof.  I'd then have a cold roof on top of that before your roofing material.  
Anything someone can design, I can sure figure out how to fix!
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Offline Don P

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Re: First Timber Frame Build
« Reply #11 on: January 30, 2019, 07:16:37 PM »
I was thinking of checking with solid board sheathing when we get there but good point Brad.

I suspect the truss is ok with purlins over it depending on joinery. Generally if the heeljoint can handle the thrust the rest can be made to work. Aligning the purlin over the strut there would be "correct". Timber screw them down and use timber blocking between them. Let's do some easy checks to see if we're in the range first.

Purlin check; 4'x8' tributary area bearing on the purlin, 32 sfx 85psf=2720lbs
4x is dimensional lumber, calc here;
http://forestryforum.com/members/donp/ddsimplebeam.html
load 2720   Duration 2 month
span 96      Repetitive No
width 4       Size 2x8
depth 8       Wet No
#2 EWP      Incised No
"Show Result"
Barely passes in bending at 4' spacing, you have some purlins a little over 4' oc I think, we're pushing it.


The shed rafters are heavy timber, calc here;
http://forestryforum.com/members/donp/beamclc06b.htm
Trib area 8x10x85psf=6800lbs
load 6800
dead load 1200
Span  120
Width 5.25
Depth 10
#2 EWP
"Show Result"
Fail
I'm coming in at 8x12

Time to rethink things

On the tall slender posts with a joint in the middle third I was more worried about buckling, that goes away with the continuous line of girts around the 9' level bracing the posts from buckling in that direction. That gives an effective column length of ~9' rather than 14', and reinforces the notch zone much better. If you want to eliminate them that is something to alert the engineer to. I'm not going to check them at this point, Double check me but I think we have a problem to solve first, are you going to 8x or tightening up bent spacing.
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Offline aguaman99

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Re: First Timber Frame Build
« Reply #12 on: January 30, 2019, 08:54:55 PM »
I'm confused about the roof.  Are there rafters?  If so what are they?  You can't just span 4' with a 1x4 laying on it's face.  Also, where are you located?  You can put your location in your profile and it will show up in your posts.  If I were you I would plan an insulated roof.  I'd then have a cold roof on top of that before your roofing material.  
As i mentioned in the original post the final roof details are still being sorted out so my spacing and design are in flux there. ...  I wasn't really ready to talk building envelope yet, i was more interested in the main frame and timber sizing so i just included a 15 psf dead load for calculation purposes to work within for now. Don has confirmed that its close so I will be making some tweaks there for sure. To address your specific questions I can only tell you where I'm currently at in my thought process. Yes on the upper roof there are of course the main bent rafters. Then perpendicular 4x8 purlins as well. The 1x4's are then added for "some" additional support and nailing, they are parallel with the main bent rafters and perpendicular to the purlins as you have demised (these could become 2 x4... or maybe ill add an addition purlin... just not sure yet). The roofing membrane starting with the layer attached to roof framing first will likely be as follows: 1 x 8 pine shiplap (maybe 2x), layer of 1/2 osb,  4"  foam, vapor barrier, 2x4 laid flat creating 1 1/2" air gap and nailers for the corrugated metal. The 2x4's will hang over 10 1/2" with a continuous barge rafter to create the over hangs. this entire membrane and timbers comes in at about 11 psf. I'm trying to design to a very efficient heat loss standard but also maintain the old world look at the same time so im going to get creative on you guys ;-). Similar details will be introduced to the entire envelope.  Hope that helps.

Offline aguaman99

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Re: First Timber Frame Build
« Reply #13 on: January 30, 2019, 09:00:27 PM »
Oh sorry, its northern Idaho and ground snow load at my specific elevation is 70 psf. I've factored in some cushion as I'm design to the 70 psf for my roof snow load to start out with until we get further along. I appreciate your feed back and certainly intend to focus on the roof details next ;-)

Offline aguaman99

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Re: First Timber Frame Build
« Reply #14 on: January 30, 2019, 09:38:30 PM »
I was thinking of checking with solid board sheathing when we get there but good point Brad.

I suspect the truss is ok with purlins over it depending on joinery. Generally if the heeljoint can handle the thrust the rest can be made to work. Aligning the purlin over the strut there would be "correct". Timber screw them down and use timber blocking between them. Let's do some easy checks to see if we're in the range first.

Purlin check; 4'x8' tributary area bearing on the purlin, 32 sfx 85psf=2720lbs
4x is dimensional lumber, calc here;
http://forestryforum.com/members/donp/ddsimplebeam.html
load 2720   Duration 2 month
span 96      Repetitive No
width 4       Size 2x8
depth 8       Wet No
#2 EWP      Incised No
"Show Result"
Barely passes in bending at 4' spacing, you have some purlins a little over 4' oc I think, we're pushing it.


The shed rafters are heavy timber, calc here;
http://forestryforum.com/members/donp/beamclc06b.htm
Trib area 8x10x85psf=6800lbs
load 6800
dead load 1200
Span  120
Width 5.25
Depth 10
#2 EWP
"Show Result"
Fail
I'm coming in at 8x12

Time to rethink things

On the tall slender posts with a joint in the middle third I was more worried about buckling, that goes away with the continuous line of girts around the 9' level bracing the posts from buckling in that direction. That gives an effective column length of ~9' rather than 14', and reinforces the notch zone much better. If you want to eliminate them that is something to alert the engineer to. I'm not going to check them at this point, Double check me but I think we have a problem to solve first, are you going to 8x or tightening up bent spacing.
thank you so much for your help here, i tried using your calculators on my own and i just wasn't confident enough in what i was plugging into them and where I was pluggin it ;-).  looking at some of your parameters and your preliminary analysis as  "close" I'm curious if we cant get there with 6x if we look at a few more things.... 
1) At the shed roof did you calculate in the 16" OC rafters between the bents?
2) At the upper roof what if i add an additional Purlin or a rafter scenario similar to the shed roof, could one of those options get us past the bending issue?
3) I stated that the roof snow load was 70 but in actuality the ground snow load is 70. I assume it would help quite a bit if we use the roof calcs rather than the higher ground calcs. I didn't know how to calc that so i just kept the error margin in for now. I'm guessing we will be at least 10% better at around 75 psf vs the 85 we currently have in there.
4) lastly, I could go with DF if I had to and that would definitely help. the current design is 20% more expensive in DF so id prefer to not have to go there....  

Offline Don P

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Re: First Timber Frame Build
« Reply #15 on: January 30, 2019, 10:20:18 PM »
AHA, Western White Pine. Groan, a little weaker in bending. Idaho, I was wondering how you knew what a moment frame was :D.

On the shed I'm looking at the pdf "prelim roof framing 1.28.19", purlins on 4' with 1x4 over on 16" ctrs. Common rafters would certainly change that.

I haven't checked the upper roof truss itself at this point, adding more purlins would certainly help with the purlin bending issue. Purlins on 32" ctrs with 1" board sheathing, foam, vertical strapping, osb, metal would probably work.

I use ground snow load, yes you can play games with a slippery roof to lower the design numbers. I've also had ice stick, then snow pile up and not slide, there is also potential impact and surcharge load on the shed from the upper roof. I'm conservative, that's getting into engineer land.

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Offline aguaman99

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Re: First Timber Frame Build
« Reply #16 on: January 30, 2019, 11:09:21 PM »
gotcha, I'm totally respecting your guidance here. let me take what you and Brad have offered and play with it some more in the 6x scenario. Ill be back in a few days with something to look at that is more concise and thought out. Actually from California but leaving and going back to Idaho thank goodness ;-). I work in the SF area and I'm a PM in the commercial construction industry so i cross paths with structural engineers most days ;-). I total get the conservative approach and it makes sense. Thank you so much for your help so far guys! 

Offline ljohnsaw

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Re: First Timber Frame Build
« Reply #17 on: January 31, 2019, 12:16:32 AM »
 :P
John Sawicky

Just North-East of Sacramento...

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 Don P

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Re: First Timber Frame Build
« Reply #18 on: January 31, 2019, 08:36:16 AM »
Sounds like a plan. I need to put the design numbers into the calcs for your species. In the 2-4" table Idaho white pine is in the species group labeled "western woods" so look for that when I get it up. It is better than EWP in that table in those 2-4" dimensions.

 In the heavy timber calc they list "western white pine" on its own under that name. I'm also going to insert "western woods" while I'm in there. That group carries the same design values as eastern white pine. If you look closely, western white pine is 25 psi lower in bending, 5 psi lower in shear and slightly stiffer than EWP in that table so use "western white pine" when you are doing anything 5x5 and larger. This is all kinda splitting hairs but might as well start as close to correct as we can.

We're up to 14 and I need to go drop an oil pan and dig out a pump, I'll play with the calcs when I get back in. Oh joy :D
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Offline aguaman99

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Re: First Timber Frame Build
« Reply #19 on: January 31, 2019, 09:46:34 AM »
sounds fun! question... i was referring to Douglas Fir as my alternate species, is that what your referring to by western woods? 


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