32' clear span

hey all, im new here so ive been trying to search for this but have come up short.
i would like to clear span 32' if possible, maybe 30' if i'd have to. i live in vermont so there is snow, and the roof pitch would hopefully be 8/12. i'll be building it myself. looking for advice or documents on beam size or what type of truss to build and all the correct specs to correctly span that distance. it will be a sugarhouse so the middle 2 bints need this ability and there will be a cupola on the peak too. thanks in advance for any help! TFG is a great site!

On the upper right of the home page of the Guild website, there is a link for finding an engineer. You should find about 12 engineers that serve the TF community in Vermont. Perhaps you can easily find a compatible engineer nearby. Additionally, you can find in the Guild store Historic American Roof Trusses to help with general information. I would caution against mimicking patterns of trusses and try to understand the mechanical problems of joints as well as timber sizing, along with forces in static equilibrium in a truss.

Take care

Hello...and Welcome!!

Wow...32'...!!...and with a 8/12 pitch...??!! Plus you're in my neck of the woods of Vermont!! Those snow loads alone are going to be challenging...

You're not going to find much out there in the Timber Framing world with that kind of direct information without paying someone for it...(most likely?)

As soon as a timber frame design starts moving outside the box of the average, then it becomes more custom and/or unique...That means somebody worked really hard on a design and it most like has been seen by a PE with timber framing experience...

You can find Roof Truss Span Charts (stick built) and related info, as well as Wood Species Load Data...However, this then takes a lot more experience than most DIYer timber framers are going to have to get a design going that is safe...

I do love the idea of what you are trying to achieve...!!! Hats off to you for trying your hand at something so bold. I have designed and cut a few Sugar House over the years, and currently finishing up on a huge project in Wisconsin that has similar Bent and Bay spans to perhaps what you are looking for...



More video and photos of the project can be found at Menomonie Farmers Market ...Feel free to contact me if you have more questions...

Regards,

j

Troleu,
Are you certain that you can't drop any posts into the building's interior? It would make the engineering an order of magnitude simpler.
That's not to say it can't be done. I've spanned longer. It's just a lot more complicated to cut a trussed frame like that. More complicated engineering, more technical high performance joinery, etc.
If you could deal with center posts. You could potentially support common rafters at the peak, making the building very simple to engineer, cut, and raise. That would be the "sever gordian knot approach" of completely sidestepping the complication issue.
The frame that you are proposing is pretty challenging for someone with minimal experience. Which is not insurmountable, but you should realize that going into it. I would say that king or queen post trusses will be the simplest for this pitch and span, but as others have already mentioned, have them looked at by an engineer.
We'll look forward to more questions!

Yep...What Hylandwoodcraft said...!!!

I love the Gordian Knot comment and in large span frames...that post makes the difference between lots of heady engineering and high end (aka quality joinery) that goes with a much (MUCH!!) simpler timber frame project...Central (or even Eave Post) configurations make things so much simpler...

Sugar Houses typically are very narrow and long...not square so I would consider that also...

If a Sugar House 32 feet wide, then by average historical proportions the Venting Monitor would be at a bout 40 to 50 feet in the air and the building would be about 50 to 80 long...

I think the widest (well proportioned) Sugar House I have seen is about 24 feet with Cat Slide (aka Salt Box) broken even roof and half length lean to on the back for wood. Its Venting Monitor was only in one bay so it to had a central post...

A continuous/full length 32' bottom cord and a king will be hard to beat. Drop the rafter down the king and in from the ends on the tie and lodge the purlins on top of the rafters. Should be straight forward for an engineer and simple to execute. Use bypassing purlings as longs as you can get.

I agree for the most part Tim...yet the pitch on Troleau's proposed structure is really low for I snow load areas...

He wants to add a venting monitor as well, and in my experience those monitors (we are doing one now) changes a great deal of the design away from King and into Queen Post truss systems...Which is more difficult. Just taking and adding a monitor to a King post doesn't work either as the load parameters change somewhat dramatically on lower pitch structures...especially over 24'.

We all agree (I think?) a PE really needs to be part of this build...

Question for the OP and others, how important is a monitor style roof in sap making? Why go through the extra effort and complicity?

hey all, thanks for the feed back so far. so i do carpentry for a living, have built a few timber frames, own most of the equipment to do all the work and the biggest reason i ask for such a specific design is because ws have a woodmizer and 321 acres to pick and choose from so im just kinda picky i guess. the ventilator cupola will be fully functionable because i do not want the steam stacks out the roof. we live on a pretty populated road so thats a big factor in making our frame idea unique. i would like to center our 4x14 arch so that gets rid of the center post design. i could downsize to 26' if need be but i just vwanted to build it big enough once instead of the maple industry way of doing it and wishing i went bigger. our town is bristol vt so the snowload is a big factor. could possibly ho 10/12 for pitch too but i dont want it looking like too much roof from the side view. my next step is to contact an engineer but was trying to avoid doing that right away. thank you all for the replies already.

trent

Hi Trent,
It's good to know that you have some experience. It's all doable, it just needs a little engineering. Like the saying goes...all it takes is time and money!
A king post would certainly work, but I might lean more towards a queen post. Then you can use common rafters and support them more mid-span. At 30' wide those rafters will be pretty long, so it will be good to support them. That arrangement might make the venting cupola easier to frame as well. I assume you will put on steel roofing? That will help with snow load, but I would still go 10/12.

Hello Trent,

I agree completely with Sean (Hylandwoodcraft)...

A Queen Post system would really be superior to a King Post system considering your design parameters of a lower style pitch, no central post and a fully functional Venting Monitor.

You should get a PE as soon as possible for peace of mind alone. If you do choose to forgo not consulting a PE with timber framing experience. I would suggest going with much bigger timbers than you probably need, and building a scale model that you can load to failure while observing deformation of the model frame's joinery.

There is also (blasphemy...I know) precedence for adding metal rods or wedged straps. Post and Beam designs with these metal components could span the desired 30' (or more) with just some key hardware in strategic locations. Its not out of context historically either, and much easier to build and engineer...I can think of several designs that I could do under these parameters that I probably wouldn't bother my PE with since it would be for my own use...(as is the case with you)...and this isn't a Public Works Project. Metal sometimes just makes things SO MUCH easier...we could be done with our current project if we had employed more metal, but wanted the challenge of using as little as possible and designing for joinery only...

Good luck, and look forward to updates or more query...

Regards,

j

Blasphemy, Jay! But if you must.
https://www.youtube.com/watch?v=9A0yFHuZs2A

Yikes...!!!!...Terrifying Video...

I was thinking more along the lines of Green and Green style metal straps and some wedges. Many of the timber frames (usually Church, Cathedral or Theaters) that pushed the limit for span would employ these at critical locations like the joinery between Queen or King post and Tie Beam...

Just this little bit of traditional Iron Work and things get much stronger and can span further...but...it is metal. It seems to be the...go to...for many and I wish more effort was made to just engineer it with all wood joinery. Nevertheless, if metal is necessary (or makes things fiscally viable) then let it be traditional...

Whew! Watched the video, and boy, NOW I realize it. The wasted years I've spent timber framing! My wasted youth, never to be reclaimed! Where were you all this time steel agricultural utility building framing?!
Thanks Tim, for taking the scales from my eyes, and awakening me to my TRUE calling in life!

I know, Hyland... it just makes those creative juices flow! I missed my calling too.

I hear ya, Jay. I put some through bolts in a some splices on my last frame. o:

If you ever get down to NH, stop in Warner (Exit 9, I-89). Behind the library on Main Street you can see the "raised bottom chord trusses" we used on this outdoor stage. The advantage being more headroom at center span.

http://mainstreetwarnerinc.org/