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Clear Span Roof Truss Calculator

Started by Sedgehammer, February 05, 2019, 12:00:58 PM

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Sedgehammer

Quote from: Don P on March 21, 2019, 07:24:35 PM
Check out fig 4-25 here;
https://docplayer.net/22941914-Heavy-timber-frame-construction.html

When we came up at 6x12. well going back pages of memory that I'm not going to dig back thru, the timber size was for a truss with no webwork, the top chords spanning 18'. The web members support the top chord so its size can be reduced structurally, but nothing wrong with being larger than structurally necessary if it looks good to your eye.
Working w/ Ben and Griff from Fire tower. Good guys. Thanks for the di rection!
6 x 12 w/ web braces are fine
12 x 12 w/ out
Leaning towards 12 x 12 for a cleaner look
Necessity is the engine of drive

Sedgehammer

Necessity is the engine of drive

cib


Removed comment. I don't want to derail the thread.

Don P

cib, normally I'm the worlds worst about jumping off topic in a thread, but, I think repost this on the barn thread you started a week or so ago and lets put the evolution of your design there, I think it'll go to more than one Q&A round before you are done.


cib

Removed the comment. I don't want to derail the thread. I was thinking this was more of a general question thread than a specific. Sorry for the mix up.

Sedgehammer

Update. 

6 x12s are fine without bracing. Griff had one truss in his calculations instead of 3. 

I do have question though. If one was to use 3 x 12s 24" OC, how big would the ridge beam need to be you figure?
Necessity is the engine of drive

Don P

I am interested in seeing what you and they come up with. I also think it would be inappropriate for us to begin walking you down the path of reworking a design you all have been, and are, working on.  I do want to see it evolve, it is different and cool. I was downright intrigued by the post tie connection details y'all came up with in the last post, that took a few head scratches to figure out :).

Sedgehammer

Quote from: Don P on October 28, 2019, 11:30:19 PM
I am interested in seeing what you and they come up with. I also think it would be inappropriate for us to begin walking you down the path of reworking a design you all have been, and are, working on.  I do want to see it evolve, it is different and cool. I was downright intrigued by the post tie connection details y'all came up with in the last post, that took a few head scratches to figure out :).
What I posted is what I had my brother draw up and they said it passes loads. Nothing need be changed thus far, but they have asked me have the architect place it in the room just to be sure.

Reason I asked the on the a ridge beam is I want to compare costs. we're gonna have a fair amount of money stuck in the metal/work alone and I just want to make sure we're in the same county as the ball park....... 
Necessity is the engine of drive

Sedgehammer

here's a link Ridge Beam from another thread on ridge beams of SYP. I would think DF would even have better loads, but if this link provides what I was asking about, what size would it need to be based on 36' ft width and a 14' clear span? Would one use 20 psf dead load and 20 psf live load?  
Necessity is the engine of drive

Don P

That table works for SYP 2x's built up into a beam.
For dougfir 2-4" thick use the dimensional simple beam calc in the toolbox here, if 5x or thicker material use the heavy timber drop down calc.

Scroll back and you'll find the design loads we were using before, It is probably noted on the prelims you are getting from Firetower as well.

For load on the calc, the ridgebeam is carrying half the roof width, 18'. The tributary area bearing on the ridge is 18' x14'=252 sf x 40 psf (if that is the design load) =10080 lbs

Sedgehammer

Quote from: Don P on October 29, 2019, 04:58:08 PM
That table works for SYP 2x's built up into a beam.
For dougfir 2-4" thick use the dimensional simple beam calc in the toolbox here, if 5x or thicker material use the heavy timber drop down calc.

Scroll back and you'll find the design loads we were using before, It is probably noted on the prelims you are getting from Firetower as well.

For load on the calc, the ridgebeam is carrying half the roof width, 18'. The tributary area bearing on the ridge is 18' x14'=252 sf x 40 psf (if that is the design load) =10080 lbs
no prelims from Ben or Griff yet, but I just emailed Griff and he just answered.
Roof Dead Load = 20psf
Roof Live Load = 20psf
Roof Snow Load = 10psf
So that adds up to 50 psf rather than 40 psf? If so, 252 sf x 50 psf = 12,600

On the DF grade, what's B+S & P+T?

the beam calculator is asking for total and dead loads. We used 20 psf live load and 10 psf dead load, which you said equaled 30 psf total load. You are using 40 psf now, which is fine, but what should go in both boxes?
Necessity is the engine of drive

Don P

Total load is 40 or 50 psf. Live load is never less than 20 psf (wind). Generally if you have design wind load the snow is gone, but, it could be unbalanced collecting on the lee side, this is what the engineers are for.
Dead load is 20 psf
P&T is posts and timbers, roughly square timbers, within 2" on each face
B&S is beams and stringers, rectangular sections, probably what you are using. 

Sedgehammer

thanks!
6 x 16 passes, would likely go with a 8 x 16 though. I'll price this out. 
Necessity is the engine of drive

Sedgehammer

Quote from: Don P on October 28, 2019, 11:30:19 PM
I am interested in seeing what you and they come up with. I also think it would be inappropriate for us to begin walking you down the path of reworking a design you all have been, and are, working on.  I do want to see it evolve, it is different and cool. I was downright intrigued by the post tie connection details y'all came up with in the last post, that took a few head scratches to figure out :).
Ben's calling me in a lil'bit. He want's to scrap the 3 trusses and go with 2 parallel timbered beams spanning the short way about 10' apart sitting on big timbered posts and then use rafters set on top. Do you know if one can still buy the laminated ceiling/roof decking like your pa used in those beautiful houses he built? thanks
Necessity is the engine of drive

Don P

I'm right certain he was Solomon's temple engineer, if anyone knows of a supplier it's him.
This is a list of the glulam listed manufacturers, each does a different range of products;
https://aitc-glulam.org/index.php/manufacturers/
This is one that is relatively close to you, I've linked to their timber decking page,
http://www.glulamstructuralwood.com/products/Disdero.pdf

Sedgehammer

Thanks a lot.

Moved ahead on lot's of fronts with Ben this evening. Decided to drop the 3 metal/wood combination trusses for a variety of reasons. Going with large posts that hold the 2 larger timbered purlin beams 10' apart, then running 3x or 4x12 rafters over them. I think 3x12 DF pass @ 4' OC. If not, what's the widest they can go?

Question though. How does one fasten the rafters to the purlin beams typically? Also the rafters will be 3x12s (maybe 4x if that's the width needed to go to 4' OC ) at least. That's what is in the rest of the house and I think it'll not look right if it doesn't match or what do you think?

Also thinking on this roof system. What about running 2x4s as purlins edge up over the ceiling decking, putting in R13 fibergalss batts in, then screw OSB through the 4" polyiso insulation to the 2x4 purlins. That'd be a R 39.6 roof. Bad thing is the 4" polyiso is a $1.81 per sq ft. 3" I can find for $1.48 used, but in Denver or Dallas. R there is about 30. Doing it this way would be a lot more stable in our windy local me thinks.

Just a thopught, if I went with 2x6s instaed, how'd you fasten them besides drill straight done through it and screw it?
Necessity is the engine of drive

Don P

I'm glad you had a good conversation, it sounds like things are settling. If you want to match the rafter sizes with the others in the house let him know, that might play into his dead loads. The connection details are part of what they will be providing. I can't help with the insulation build up, again work with them on those details.  

Sedgehammer

I emailed him on both topics before i posted, but I was wanting some objectivity if possible. That's how the best idea's usually are formed. The main reason we dropped the other idea was it just was going to look too cluttered, but my layout/design passed there design values all the way around. If my memory serves, didn't/don't you use something similar roofing on some cabins you built? I just cannot remember for sure where I saw that.
Necessity is the engine of drive

Sedgehammer

Here is what i found today. I'm sure you know what it is Don, but in case anyone else doesn't. This gets screwed to the roof decking and then you screw into the roof purlin (?).  Would you fasten it in a different way?



Necessity is the engine of drive

Sedgehammer

@Don P Didn't you have some cabins you used polyiso on the roofs? How'd you build those out? Thanks
Necessity is the engine of drive

Don P

I'm just back from measuring "granny's house" on this family compound for a remodel. Anyway, this is what we did, 5" of polyiso over the 2x6 T&G roof deck, 2x4 strapping, ply and shingles.


 

 

Sedgehammer

Looks like you just glued the iso to the decking, then screwed the 2x4s through the iso to the decking, then screwed the ply to the 2x4s. Amiright, amiright.....;D
Necessity is the engine of drive

Don P

No glue, all screws and nails. Every other 2x4 is over a 4x10 FOHC dougfir rafter so those screws go thru 2x4, foam, decking and into the rafter. every other 2x4 is just screwed into the 2x decking. then the ply is nailed to the 2x4's.

That was the detail on that job, sitting here I can think of a couple of other ways we've done it, just depends on the plan detail provided.

Sedgehammer

Ahh k. Ben didn't specify any certain way to do it just yet, he just told me come up with a couple of different ways and he'd see if it works or not. He liked my 2x6 purlin 2' OC with R23 batts and then 2.5" iso glued to the purlins, then 5/8 OSB screwed thru the iso into the 2x6 purlins. That's why I was looking for ways to fasten the 2x6s to the decking. He suggested just cross screwing, but I'm not a fan, so I will use those clips every 2', then drill and screw into the decking and where there are rafters into them at 4 points in the purlin, plus i'll lay a bead of construction adhesive under the 2x6. That's what I came up with so far. Over kill? 
Necessity is the engine of drive

Don P

You'll need to attach the edges of the ply on something like 4-6" centers, 12" in the field so think about getting that done effectively, APA's help desk might have some ideas or their site might have some ready details, apawood.org I think. Glueing on the job is considered structurally to be zero, way too wild an environment. For instance its 12 degrees out there right now and we just decided to hold off crawling up on the roof for a couple more hours, so all depending on the work day you can be trying to apply against weather, temp, wet, etc with unknown gaps and clamping efficiency. Make sure your mechanical fastening is up to snuff, we were screwing those 2x's on I think 2' ctrs but your uplift probably controls, and consider glue to be gravy.

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