Clear Span Roof Truss Calculator

[Don P]

I'm thinking a 4x12 ridge, align the rafter bottoms with the bottom of the ridge, the tops will poke up about 5/8" over the top, if that's objectionable a beveled 2x4 cant strip could fill the gap.

If you run the plates up the sides of the rafter and weld a cap plate over the top, better yet inset it flush, you've trapped it. Weld fast and douse it quick. The connection is eccentric but if the steel is heavy enough to not twist. Ben Brungraber at Firetower handed out some pics of historic iron "shoes" for restraining that connection, I'll see if I can dig something up. In old timberframe buildings and bridges it was very common to have steel or iron in high tension places like this. At that time he was working on a large truss that had over 70,000lbs of thrust at the heel. His comment was that if you can resolve the heeljoint the truss is usually buildable.

Here we go, this was just a quick google @TimberHawg1 might enjoy these as well, first 2 are old engineering texts the third is a current company but there are pics of new and old work, Greenoak uses stainless nowadays for their steel work;
truss heels
timber roof construction
Hit around pgs 15-20 here for some interesting trusses; https://www.greenoakcarpentry.co.uk/wp-content/uploads/2016/09/What-Designers-Need-to-Know-about-Oak-Framing.pdf

[Sedgehammer]

If one was going to use 10x10's or 12x12's for doorways or openings/archways, what can one expect for end and width shrinkage?

Thanks

Your post didn't show up on my phone, I'll check out what you linked and post on it later tonight or tomorrow. 

[Don P]

In length normal wood doesn't shrink appreciably. In width 1/4 to 3/8" from green to in service moisture content, that varies considerably. Where you chose to fix the connection plays a large role in the direction the shrinkage moves things. For instance with the post at a door if you pin the post closer to the jamb the post will stay tight to the jamb but the opposite face will move towards the pin. In the case of your plates pin them low, close to the bearing notch so that the notch will carry the load rather than the pin. When bolting, bolt low, near the bearing and do not space bolts more than about 5" apart across the face width of a piece of wood to avoid drawing the wood apart and splitting it between bolts.

[Sedgehammer]

Can do both

Yes, he's pretty much correct. The thing we need to remember is that there are 8 other rafters that are all carrying the same load more or less, so while it's important to lock them down, I don't think the 'one' needs to be overly worried about. I was planning on some serious metal to keep everything lined up and secure. With that said, I kinda like the u-bolt approach. I think it adds some 'look' to it, plus making it very secure.

Some of that in those diagrams/pictures is just crazy.... Way above my pay grade that's for sure..... I do marvel in how things were made pre-powered tool era. Museums can be a favorite of mine.

In length normal wood doesn't shrink appreciably. In width 1/4 to 3/8" from green to in service moisture content, that varies considerably. Where you chose to fix the connection plays a large role in the direction the shrinkage moves things. For instance with the post at a door if you pin the post closer to the jamb the post will stay tight to the jamb but the opposite face will move towards the pin. In the case of your plates pin them low, close to the bearing notch so that the notch will carry the load rather than the pin. When bolting, bolt low, near the bearing and do not space bolts more than about 5" apart across the face width of a piece of wood to avoid drawing the wood apart and splitting it between bolts.

Gotchya on the shrink

Ya kinda lost me on the rest  Remember I ain't a timber framing guy 

[Don P]

Well you hopped into the pool, start paddling
I'm just messing with you, holler whenever I lose you

The tie is what makes that one rafter couple critical, it supports the ridge and the adjoining common rafters then hang from the ridge. It is a "post" supporting the ridge at midspan, the rest hang from the ridge. Load goes to stiffness, this is our hard point. If you are looking at them all contributing equally than you would look at the plate stiffness in bending across the 8' spans between tie points against the horizontal thrust load, that would be the stiffness, we haven't done that. Another way of doing it is to size the ridge so that it can support the roof from wall to outer gable with the rafters hanging from it and calling the steel tie gravy, or eliminating it. Double the ridge load above and 16' span in the calc. What you just described is kind of getting into hope or unconservative thinking, it might work but is not a good way to go unchecked.

For post and beam, steel connected heavy timber, the glulam folks are the standards writers. This is their main publications page;
http://www.aitc-glulam.org/Shopcart/index.asp The Timber Construction Manual is the standards reference. I have a copy here, you can probably get it through interlibrary loan and it does detail truss construction but kind of at a deep end of the pool level. Still might be worth checking out. "Design of Building Trusses" James Ambrose, is another good reference at more of a builder's level. "Simplified Engineering for Architects and Builders" Parker and Ambrose, has a very good section on truss design.

This detail excerpt from the AITC manual shows some of what I was talking about above as far as good and bad connection methods, click it and roll through the pics to see best practices;
http://www.aitc-glulam.org/Shopcart/Pdf/aitc_104_2003.pdf
Think about how, where and why they connect where they do, especially go to pg 27 and read those prohibited connections and understand them.

[Sedgehammer]

No, no, I got all that

It's this part 

Where you chose to fix the connection plays a large role in the direction the shrinkage moves things. For instance with the post at a door if you pin the post closer to the jamb the post will stay tight to the jamb but the opposite face will move towards the pin. In the case of your plates pin them low, close to the bearing notch so that the notch will carry the load rather than the pin. When bolting, bolt low, near the bearing and do not space bolts more than about 5" apart across the face width of a piece of wood to avoid drawing the wood apart and splitting it between bolts.

I have an idea'r   But not more than 21.9%...... 

[Sedgehammer]

Don, while you're replying on the door/archway posts I thought I'd post on the interior stuff & anyone else with idea's, please chime in

The idea is to have a cathedral ceiling with exposed rafters preferred. Of course by doing that, it requires another roof to be built on top of it, so we can achieve R38 insulating value. We would prefer to have the 6" t&g pine or the 8" t&g hardwood as the ceiling vs rocking it. Don, on the exterior roof system you had said 2x12's work on 24" oc. I am wondering if 3x12's work on 32" oc.....

32" oc would be 7 rafters plus a half. This could be made up on the interior wall side of the house a few different ways, so for now lets say 7 rafters. Was thinking of something like this, with the 3x12 piggy backing the metal truss on truss 2, 4 & 6 or replacing 2, 4 & 6 entirely. Would need to still have a piece of rough cut on top of metal truss for ceiling to attache too though.  





If 32" oc doesn't work, could do something like this on 24" oc. 20'x6" c-channel with 24"x12"x1/4" plates welded to both ends and either 1/2 chain with a threaded eye bolt for tension bolted through and to the exterior wall with a plate on the exterior side and/or to the end of the rafter heel or 2"x2" sq tubing welded under the c-channel to the outside wall plate and/or to the rafter heel





With all that, we are not 'married' to any single idea, but we are trying to do something different without getting too exotic though. I can build pretty much anything metal and can work with wood, but am not a timber finisher by any means. Worst come to worst we could build a "pole barn" type RC truss, but really do not like the look all that much.

Thanks

[Don P]

Whoops, we're on top of each other but I'll post the reply to the post Q and then read this latest post.

If I'm understanding the question right. Imagine a 12x12 post standing on a slab. If I bolt a piece of angle iron to the floor on the door jamb side of the post and bolt the upright leg of the angle to the post, as the post shrinks the door jamb side of the post will not move. As the post shrinks the far side will move towards the point of attachment, the angle clip.

Same thing if you bolt a horizontal beam to a notched post. If I put the bolt or peg through the beam into the post down low on the beam, close to the notch the beam will bear on the notch as it shrinks. If I put the pin at the top of the beam and into the post, as the beam shrinks it will lift off the notch and hang from the bolt. The beam will likely split at the bolt. That is shown in pics in the second link in my post above. Scroll through that and think about what they are showing, good stuff for post and beam or timberframe builders.

[Don P]

I'll let you walk through the rafter check, talk me through it like I did above and I'll spot you.
Also try 3.5x11.25 dougfir @4' oc.

The easiest way to do a cathedral ceiling is a structural ridgebeam with rafters hanging from it.
Sounds like a 20' span? 18' tributary width... half of each rafter is bearing on the eave wall, half is bearing on the ridge x 30 psf=540 lbs per lineal foot on the ridge. Glulam table here;
http://www.aitc-glulam.org/pdf/Capacity/DF_26.PDF
Looks like a 5-1/8x13.5 would work.

Then 2x T&G decking. That looks good, is readily available and pretty fast to dry in. Does that solve it or do you want to keep going with the above?

[Sedgehammer]

Whoops, we're on top of each other but I'll post the reply to the post Q and then read this latest post.

If I'm understanding the question right. Imagine a 12x12 post standing on a slab. If I bolt a piece of angle iron to the floor on the door jamb side of the post and bolt the upright leg of the angle to the post, as the post shrinks the door jamb side of the post will not move. As the post shrinks the far side will move towards the point of attachment, the angle clip.

Same thing if you bolt a horizontal beam to a notched post. If I put the bolt or peg through the beam into the post down low on the beam, close to the notch the beam will bear on the notch as it shrinks. If I put the pin at the top of the beam and into the post, as the beam shrinks it will lift off the notch and hang from the bolt. The beam will likely split at the bolt. That is shown in pics in the second link in my post above. Scroll through that and think about what they are showing, good stuff for post and beam or timberframe builders.

Okay, got it. 
Was planning on overhang the horizontal beam 3 " on each side. Then notching them as wide as the studs. Fastening the stud to the vertical beam and 'now' only down low to the horizontal beam. The floor joists would rest on the horizontal beam. 6' opening with 12x12 rc df & 3' opening with 9x9 rc df no floor joists above it.

[Sedgehammer]

I'll let you walk through the rafter check, talk me through it like I did above and I'll spot you.
Also try 3.5x11.25 dougfir @4' oc.

The easiest way to do a cathedral ceiling is a structural ridgebeam with rafters hanging from it.
Sounds like a 20' span? 18' tributary width... half of each rafter is bearing on the eave wall, half is bearing on the ridge x 30 psf=540 lbs per lineal foot on the ridge. Glulam table here;
http://www.aitc-glulam.org/pdf/Capacity/DF_26.PDF
Looks like a 5-1/8x13.5 would work.

Then 2x T&G decking. That looks good, is readily available and pretty fast to dry in. Does that solve it or do you want to keep going with the above?

I cannot figure out how to change spacing unless I got the wrong link, but I looked at 3 of them

Prefer to run the ceiling parallel with the house walls, but I guess that's possible with 2' DF on 4' oc. I don't know where that's available right at the moment though or price point

Since I have to build another roof on top of it, would the live load be double?

No glulam and I cannot put that much weight on the interior wall end, as no direct post/wall underneath. It's offset about 18". Could put a double floor joist right there though. The other end is the fire place, but that most likely will be built later. Not going block all the way. Am leaning towards using a stainless chimney and using steel primed black on the inside above the mantle to ceiling tapering and angling as it goes the entire 27'. Would have a riveted look, but just with 5/16 square headed bolts

[Don P]

Gotcha, no bearings for a structural ridge beam, trusses it is. Getting to be bedtime for me and I have welding class tomorrow nite, might be a couple of days before I can look hard at it. I'm not meaning to hog all the fun, you other guys can chime in.

Rather than overframing the roof another idea, 6" of foam, three layers of 2" thick 4x8 sheets would perform better than fiberglass, polyiso is around R7 per inch, XPS is R5 but either will perform better than glass.  This is along the lines of what I was thinking, these were 4x10 DF at 4' oc (narrower room and a little steeper pitch) 2x6 T&G, foam, 2x4 sleepers at 2' oc, ply and then shingles.

[Sedgehammer]

No probs, have fun, see ya later and many thanks!

Nice work! 

I'm at a 4/12 due to the fact the existing is 4/12 and I can do the roof steel myself. Plus I don't think a steeper roof would look as nice with this style of a home. What do you think?

Polyiso

6" @ R39 as 2" = R13 x $30 per sheet or about $2,100. Depending on how it's laid out, it might not be that much higher than glass over all.

5" @ R33 = $1,824

Could one screw the 19/32 osb directly to the decking if 2" df t&g with 7" screws?

Purlins vs sleepers.... After thinking on it, it's about a horse apiece I guess. One could go with 4" and then sleeper/purlin it, then go with 1.5" in between purlins since 24" oc if one needed to save the 1.5". It'd be a R33 @ $2,064.

Okay, I am on board with the polyiso. Now the easy part......

[Sedgehammer]

Ok, have a little conflict. If we go with the 5 or 6" polyiso, how do we do an exposed soffit with 8" rafter tails. 

I suppose one could nail/screw the rafter tail to the sleeper and decking below and just put the 5/8 car siding on whats exposed and run the 5/8 osb on the rest? 

[Sedgehammer]

Decking

2x8 T&G YP @ $1.64 sq ft

or

2x6 T&G DF @ $2.60 sq ft

Besides the obvious price point difference and wider wood, any advantages in using DF over YP?

Thanks

[Don P]

I'd roll through some of the syp and see if the quality is acceptable, if so and if you like the look seems like a no brainer.

If you don't mind a fascia above the exposed tails that will cover the depth required for the foam sleepers and ply then that would solve it. I prefer having that vented channel created by the sleepers, your call there.

I like playing with this truss design tool;
http://pages.jh.edu/~virtlab/bridge/bridge.htm

Here's a quick one I did to show how it works, add a 0 to every number to get the approximate forces, These are axial (along the length, axis) forces acting on the truss members. So those forces would be checked as columns. The top chord also acts as a beam supporting the live and dead loads distributed along the members between the nodes. They are designed as "beam columns" or in the NDS "Combined Bending and Axial Loading" we can preliminarily size this but your engineer will do the actual final calcs and design.





Welded up 50 coupons tonight, something smells like burnt metal and burnt fur... off to the showers

[Sedgehammer]

That's what I was thinking

..... Have to figure a way to frame in the rafter tails.... I could rip the 2' that'll go on the roof out of the 2x8 and that won't be much if I use 6" polyiso with sleeper. Then screw through the 8" of the 2x8 into the decking and then screw it to the sleeper

I hear ya on the venting part. I might have to drop down the freeze board a bit for air, and screen it for bees or drill some holes and screen them.  

Hmmm. My computer doesn't like it. Just a blank page with a small square box in the middle at the top of the page. Tried going to the school itself and it's website is fine all the way up to the truss builder 

That's kinda how I was thinking, but out at the edges would be 1' deep and at the mid points in between it, would be the web to the lower truss. Then I would weld in plasma cut designs in the 11 gauge panels.Weld them in between all the truss openings. Could maybe even go to 12 gauge.

Working on a acrylic circle LED 30" design for the middle at the peak, so would want the center to be that large clean through. Supports would have to go around it.

Coupons  You trying to be a certified welder?

Burnt fur just mean you was being busy.....

Could either go 40" center and have 3 metal ones with 3 wood ones or got to 4" oc and have just the 4 metal ones. Would have a 3x6 screwed to the top of the truss with the width being the 6", so as to have 3" to nail the syp into.

[Don P]

Try internet explorer browser and update your java with Oracle.com and see if that gets it.
The circle in the center top reminds me of the Iron Bridge in Britain, nice detail, way above my pay grade. If the truss is top chord bearing on the wall and the 2x or 3x6 on top of the steel projects out to support the tail, the tail could be applied under that, outboard of the wall, then the buildup of T&G, just brainstorming there.

[Sedgehammer]

no dice.......

[Don P]

Not a big problem, you are way out of my league, this is deep into engineer land.
Here's a sketch of what I think you are talking about for a truss;



I think it is quite do-able. As I look at it the bottom arc of the circle wants to straighten out under load and let the truss flatten, the strength of that circle is critical. The exposed tails could be attached to the extended top chord, grooved around the steel. Top chord is the bearing at the walls, the bottom chord drops down inside the walls. A nailer on top of the top chord to attach the T&G to. Is this pretty much what you are envisioning so far?

I am going for structural certification. We got a steel lintel in at work today where somebody decided to knock holes in the block walls years ago where it suited them, the inspector called for engineering and repair now that we are remodelling. We dry fitted the built up parts a few weeks ago and tacked it, then dropped them off at the welding shop, paid good money and waited and hauled. Then back to work, we dry fitted, played with them a little more, jacked into place, then put posts and post bases under them and tacked. I'll call the welder out to do the final welds then a certified welding inspector. It would go smoother if I can do the welding on site myself next time. Looks like the weather breaks tomorrow so back up top to strip more roof and do repairs then class tomorrow nite, I was getting into a groove towards the end last time so hopefully it will start to be like riding a bike soon.